Ref. Ares(2023)944027 - 09/02/2023
FINAL REPORT
STRUCTURAL THERMAL ENERGY STORAGE IN HEAVY WEIGHT BUILDINGS –
ANALYSIS AND RECOMMENDATIONS TO PROVIDE FLEXIBILITY TO THE
ELECTRICITY GRID
Client:
CEMBUREAU - The European Cement Association ASBL
Contact Person:
@cembureau.eu
Address: 55,
Rue
d'Arlon
- BE-1040
Brussels
– Belgium
3E Reference:
PR109637
3E Contact Person:
@3e.eu
Authors:
Date:
20/10/2016
Version:
Final
Classification:
ED
Unless otherwise explicitly agreed upon, 3E cannot be held responsible or liable for consequences of the
use by the client of the results, reports, recommendations or other data supplied by 3E in the frame of any
project or order executed by 3E.
info@3E eu
3E nv/sa
T +32 2 217 58 68
BNP Paribas Fortis
RPR Brussels
www.3E eu
Kalkkaai 6 Quai à la Chaux
F +32 2 219 79 89
BAN: BE14 2300 0282 9083
VAT BE 0465 755 594
B-1000 Brussels - Belgium
SW FT/BIC: GEBABEBB
EXECUTIVE SUMMARY
To overcome the growing unbalance between energy demand and renewable energy generation, an
increased flex bility is required from the demand side (i.e. the consumer). Orchestrated in a new energy
infra- and market structure, e.g. so-called smart grids, buildings can play a significant role in demand
side flex bility. Given the available inertia provided by heavyweight construction materials, and given the
increasing electrification of heating and cooling systems, structural thermal energy storage (STES) in
buildings can be one of the key actors for a successful demand response energy market, without
additional investments in storage devices. However, the current version of the Energy Performance of
Buildings Directive (EPBD) does not include the concept of structural thermal energy storage used for
active-demand response (ADR).
Considering this absence, The Concrete Initiative commissioned a study to show the potential of using
the structural thermal mass of heavyweight buildings, such as concrete buildings, in terms of potential
increase of renewable energy penetration in the grid, avoiding grid peaks, and flexibility benefits in a
smart grid context.
This report is the result of this study, and consists out of three main steps: (i) a comprehensive review of
the relevant literature, (ii) the analysis of the findings and (iii) recommendations with regard to the
exploitation of structural thermal energy storage.
Scientific literature demonstrates a substantial benefit in pre-cooling and pre-heating of buildings under
specific conditions, i.e. for a specific type of building, equipment, control setup, comfort range, time
periods for pre-cooling or pre-heating, and limited season (heating and cooling season). Most studies
focus on the benefits and possible limitations in term of energy consumption savings during grid peaks,
and discuss the requirements to use thermal mass to create flexibility on grid level to its ful potential.
In summary, those requirements are the sufficient thermal insulation of the building, an adapted fabric
cover over the underfloor heating/cooling pipes, a suitable heating/cooling system providing flexibility
such as electrical heat pump or a flexible district heating, a smart controlling, the possibility to aggregate
individual loads, and adapted energy prices incentives.
When fulfilling these requirements, the flexibility provided by the thermal mass of the building fabric can
lead to significant benefits such as the balancing of the grid infrastructure (e.g. peak reduction up to 50%
of cooling load), investment and operating cost savings (operational savings up to 40%), higher RES
penetration and CO2 emission reductions (up to 25% CO2-reductions per dwelling).
info@3E eu
3E nv/sa
T +32 2 217 58 68
BNP Paribas Fortis
RPR Brussels
www.3E eu
Kalkkaai 6 Quai à la Chaux
F +32 2 219 79 89
BAN: BE14 2300 0282 9083
VAT BE 0465 755 594
B-1000 Brussels - Belgium
SW FT/BIC: GEBABEBB
Figure 1: Schematic overview of the requirements related to the optimal use of Structural thermal
energy storage
Nevertheless, different limitations are to be considered with pre-heating or pre-cooling strategies in
buildings: a total electricity consumption increase due to storage losses, limited storage duration and
utilization in mid-season, and comfort limitations. However, when the active demand response program
is properly managed, those downsides of structural thermal storage can be addressed in order to tap the
economic and environmental benefits.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
4 / 36
provide flexibility to the electricity grid – 20/10/2016
Figure 2: Schematic overview of the benefits resulting from the optimal use of Structural thermal
energy storage
The current review of the EPBD is an opportunity to raise ambitions with regards to the exploitation of
structural thermal storage to its full potential with the following policy recommendations:
x
Evolve to new energy performance calculation models to take thermal energy storage into account.
x
Insist on new energy performance calculation models to take into account the dynamic use of
thermal energy storage in a load shifting context.
x
Improve the recognition of the benefits of structural thermal storage by taking the “available
structural storage capacity” into account in the Directive.
x
Promote the interoperability between building heating/cooling systems and the energy market in
order to deploy ADR.
x
Encourage energy storage incentives in order to make it economically viable for end-users today.
The following policy recommendations would allow better use of the storage capacity but they are
considered to be out of the scope of the EPBD.
x
Encourage experimental studies / pilot projects in real buildings to demonstrate the benefits of ADR
using structural thermal energy storage in operation.
x
Encourage energy tariff structure reflecting the demand-supply unbalances in order to provide an
incentive for ADR.
x
Align storages regulatory frameworks in order to maximize the storage opportunities, especially at
peak.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
5 / 36
provide flexibility to the electricity grid – 20/10/2016
TABLE OF CONTENTS
Executive Summary
3
Table of Contents
6
1 Introduction
7
1.1 Background and problem definition
7
1.2 Objectives
8
1.3 Scope
9
2 Methodology
11
3 Literature review
12
4 Analysis of Findings
14
4.1 Requirements and facilitators
14
4.2 Benefits
16
4.3 Limitations
19
4.4 Impact on stakeholders
22
5 Policy Recommandations
23
5.1 EPBD Revision
23
5.2 Other recommendations
24
6 Conclusion
25
7 Annexes
27
7.1 Abbreviations
27
7.2 Glossary
28
7.3 B bliography
30
7.4 Two Practical Examples
32
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
6 / 36
provide flexibility to the electricity grid – 20/10/2016
1 INTRODUCTION
1.1
BACKGROUND AND PROBLEM DEFINITION
The energy system is moving from a fossil-fuel-based, highly-energy-consuming, centralised system
towards a renewable-energy-based, energy efficient, more decentralised, and interdependent system. A
growing number of intermittent renewable energy sources (RES) are necessary to achieve a
decarbonized energy system but this also puts additional pressure on the electricity grid: the grid
infrastructure has been designed to absorb centralized electricity generation and balance the grid by
adapting this generation, while the unbalance between energy demand and supply can become a
profound issue because of RES. To overcome this unbalance and guarantee the stability of the electricity
grid, an increased flexibility is required from the demand side (e.g. the consumer). Orchestrated in a new
energy infra- and market structure, e.g. so-called smart grids, buildings can play a significant role in this
context of demand side flex bility.
Buildings in Europe are currently respons ble for about 40% of the total energy consumption. Space
heating and cooling take significant portions of this consumption. Given the possible inertia of these
thermal demands and the increasing electrification of heating and cooling systems, thermal energy
storage systems (TES) in buildings are one of the key actors for a successful demand response energy
market (1).
Opportunities are missed when seeing buildings as basic individual units using energy when needed.
The building stock in general and new buildings in particular are in a transition phase when it comes to
the design of the energy system. Buildings are moving from being highly-energy-demanding and
unresponsive elements in a system to becoming highly-efficient micro energy-hubs consuming,
producing, storing and supplying energy, making the overall system more flexible and efficient (1). There
is also an increasing potential for flexibility when using loads that can be shifted l ke space heating and
cooling, domestic hot water, white goods (such as dish-washers or refrigerators), or electrical vehicles.
The capacity of buildings to store energy is therefore an important factor in the development of smart
grids.
Considering the load-shifting potential in buildings with regard to heating and cooling, the available
thermal energy storage capacity exploiting the fabric thermal mass of a building can be used to pre-heat
or pre-cool a building. “Structural thermal energy storage” (STES) is the appropriate term for this kind of
storage since the thermal energy is mostly stored in the mass of the structural elements – i.e. walls, slabs
and ceilings – and re-released on a later moment (2). In its passive form, structural thermal energy
storage has actually been tapped by building designer for ages: passive night cooling of heavyweight
building is a traditional way to tap the thermal mass of stone or concrete under hot climate. In a smart
grid context, the active and intel igent utilisation of structural thermal energy storage is also promising.
Because it is exploiting the mass of a material that has been built for other purpose; it does not require
additional investment in storage devices.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
7 / 36
provide flexibility to the electricity grid – 20/10/2016
The current Directive on the Energy Performance of Buildings (EPBD) is mainly aiming at the reduction
of the energy use of the individual building. For instance, in order to reduce the global energy
consumption of buildings, the EPBD states that all new buildings should be nearly-zero energy buildings
(nZEB) by 2021. In the calculation methodology to verify if this goal is reached, it is mandatory to include
thermal characteristics, heating and air-conditioning installations, renewable energy technologies,
passive heating and cooling elements, shading, indoor air-quality, etc. Specifically relevant for this study,
it also refers to thermal capacity in the building construction, used to improve indoor climatic conditions.
(3)
Nevertheless, the current version of the
EPBD does not include the concept of structural thermal
energy storage (STES) used for active-demand response (ADR). This study therefore focusses on
the advantages and limitations of structural thermal energy storage, in order to suggest policy
recommendations to include this in the EPBD-revision.
1.2 OBJECTIVES
This study, commissioned by the Concrete Initiative, presents the potential of using the structural thermal
mass of heavyweight building, such as concrete buildings, in terms of potential energy efficiency and
flex bility benefits in a smart grid context.
The
objective of this study is
threefold:
x
Provide a clear definition of the concept of ‘structural thermal energy storage’, ‘thermal mass’,
‘thermal capacity’ and ‘thermal inertia’ based on current EPBD-legislation and in a smart grid
context.
x
Several benefits and limitations of structural thermal energy storage can be found in the scientific
literature. Those benefits and limitations shall be aligned, structured and clarified in order to
withhold the most promising applications.
x
Provide recommendations on policy measures that would allow to tap the potential of structural
thermal energy storage in buildings in order to reduce further the CO2 emissions associated to
building consumption. The Energy Performance of Buildings Directive (EPBD) is a particularly
relevant target for those policy recommendations since it is under revision in 2016.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
8 / 36
provide flexibility to the electricity grid – 20/10/2016
1.3 SCOPE
This study targets structural thermal energy storage (STES) in heavyweight type of buildings such as
concrete buildings.
Structural thermal energy storage differentiates from the current EPBD-regulation, as
thermal capacity
in the EPBD is described as a measure against overheating. This means that the EPBD refers to the
passive working of thermal inertia, which is the case in for example concrete structures where there is a
lot of available thermal mass.
Structural thermal energy storage intends to activate thermal mass, in order to increase the use of
thermal mass on top of its passive behaviour to store energy. This can be done through the use of
Thermal Activated Building Systems (TABS) as emission system, where water tubes are integrated in a
structural element in order to provide heating/cooling to a building. Known concepts based on this
emission type are concrete slabs emitting heating and cooling to the floor above and below, and also
floor heating where a few centimetres of a cement based solution is heated in order to heat the room
above the floor.
This approach of activating thermal mass, enables an
interesting potential on grid level due to the
time delay between heating/cooling and emission. It enables structural thermal energy storage, which
can be used in a smart grid context where moving loads can create flexibility for the grid through active-
demand response (ADR).
Active-demand response programs, managing flexibility between buildings and the grid, are mostly
applicable in a building equipped with an electric system for heating and/or cooling purposes in a smart
grid electricity context. Similar active demand-response programs are also explored in the context of new
generations of district heating systems (smart thermal systems), where local storage and demand-side
management are proposed to increase the global efficiency of the district thermal system and increase
the RES penetration (4). In order to move loads, it is important that the production unit is steered by a
smart control. Whether this is a district heating/cooling system or a heat/cold source located in a single
building, makes little difference in this context of load shifting.
In order to further align the scope of the study, it is important to elaborate on the working of an ADR. An
active demand response (ADR) program is actively exploiting the demand side flexibility (in heating and
cooling, among others) and its main impact could be summarized into three key results:
x
Peak shaving or peak clipping, denoting the reduction of the total required peak power of
buildings by reducing the required peak power for heating and cooling in buildings or by reducing
the simultaneity of these peak loads with other electrical loads.
x
Load shifting, denoting the introduction of a time delay between the system activation and the
energy demand in the room by pre-heating or pre-cooling.
x
Valley filling, denoting temporal increase of the load during off-peak periods, for example when
photovoltaic own consumption cannot be valorised otherwise.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
9 / 36
provide flexibility to the electricity grid – 20/10/2016
Figure 3: Conceptual daily load profile with and without active demand response (ADR) (2)
Whereas peak shaving could enable smaller equipment because of lower power requirements (system
ducts, plant size, smal er grid cables) thus enabling a reduced investment (CAPEX), it can also induce a
reduction of the operational cost when the electricity price contains a capacity factor. Similarly, load
shifting induces a market impact and a reduced operational cost (OPEX) when the necessary price
incentives exist.
Despite the incentive for several stakeholders, advantages on cost-level could be considered of limited
relevancy for policy recommendations as these often focus on social welfare maximization and
environmental benefits when aiming towards a sustainable horizon. For example, the potential increase
of renewable energy penetration enabled by structural thermal energy storage could be considered as
more relevant in this context.
The study therefore includes estimations towards cost savings, but
mainly focuses on the
environmental impact that load shifting induces,
i.e. the possible increase of RES penetration on grid
level, the decrease in peak-power generation and the induced CO2 emission reduction.
This means that the study goes beyond the single-building energy efficiency scope and takes into
account its flex bility by looking at the synergies between buildings, the electricity grid, the electricity
market and the generation of electricity when studying the potential and limitations of structural thermal
energy storage.
In this frame it is relevant to note that other technologies than STES can also be used to store energy in
a demand-response context (for example batteries or hot water tanks) but a comparison with other
storage technologies is not part of the scope of this study. The use of thermal energy storage is shown
to be cost effective compared to battery storage (2). Amongst the comparative advantages of structural
thermal energy storage, the low investment cost needed compared to other storage devices and the very
long lifetime of the storage that is virtually the same as the lifetime of the building.
In addition to the scope described in this chapter, two examples are added in 7.4
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
10 / 36
provide flexibility to the electricity grid – 20/10/2016
2 METHODOLOGY
Following the definition of structural thermal energy storage and how it differentiates from the current
EPBD, this chapter describes the applied approach to define policy recommendations on structural
thermal energy storage.
The methodology to achieve the above goal consists of a comprehensive review of the relevant literature
and the analysis of the findings, in order to draw recommendations around the active utilization of the
thermal mass of a building (in addition to the current validated passive working). The approach can thus
be summarized in three main steps:
1.
The
Literature Review (Chapter 3
) consists of a comprehensive overview of the results of
scientific papers and studies carried out in the EU and North America on the utilization of (active)
thermal mass and structural thermal energy storage. The list of relevant studies that have been
reviewed are available in the B bliography in Annex 7.3. Both simulation and experimental studies
from the literature have been taken into account. This review aims to collect:
-
The relevant indicators to quantify the potential of thermal mass in terms of flex bility,
-
Qualitative and quantitative results in term of flexibility and associated savings,
-
Qualitative and quantitative impact assessment in terms of environmental benefits.
2.
The
Analysis of Findings (Chapter 4) and the comparison of the different benefits and limitations
of the structural thermal energy storage on building and grid level. This discussion aims to:
-
Discuss the requirements that will enable the utilization of the flexibility provided by the
thermal mass to its ful potential.
-
Compare the relevant findings and analyse their implications for different stakeholders and
assess the evolution of those consequences in the longer term.
-
Explain the benefits that were identified in the scientific literature
-
Discuss the drawbacks and current limitations and address them when possible
3.
The
Policy Recommendations (Chapter 5) are formulated based on the literature findings and
their analysis. Those recommendations are focusing on the EPBD document and its
implementation at member state level.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
11 / 36
provide flexibility to the electricity grid – 20/10/2016
3 LITERATURE
REVIEW
Many studies have demonstrated a substantial benefit in pre-cooling and pre-heating of buildings under
specific conditions,
i.e. for a specific type of building, equipment, control setup, comfort range, time
periods for pre-cooling or pre-heating, and limited season (heating and cooling season). Most of those
studies are focussing on the benefits and possible downsides in term of energy consumption savings at
peak, while many different additional indicators are used in the literature and a wide range of results for
similar indicators can be found.
The following table provides an overview of the indicators and related quantitative results that have been
found in the relevant literature.
Table 1: Overview of results from ADR using structural thermal energy storage
Strategy
Relevant Indicators
Results
Type of building
Source
(E) : Experimental
(S) : Simulation
12 – 30 kWh/period
(radiator)
Structural storage capacity
Dwellings (S)
(2)
(load shifting – 4h period)
16 – 66
kWh/period(underfloor
heating)
-34 %
Service building (E)
(5)
30 – 100 €/participant
Electricity costs savings
Dwellings (S)
(6)
per year
Pre-
-26% to -40%
Dwellings (S)
(2)
heating
+25 %
Dwellings (S)
(2)
Heat demand fraction
+19% to +30%
Service building (E)
(5)
covered by RES
up to +6.7 %
Dwellings (S)
(7)
0.25 - 0.55 t/y/building
Dwellings (S)
(2)
CO2 emission reduction
-15 % CO2 on average
0.25 t/y/building
Dwellings (S)
(2)
+1.5% to +7.5%
Total electricity use by HP
Dwellings (S)
(2)
+5% on average
-25%
Office buildings (S)
(8)
Reduced energy supply
-25% to -50 %
Commercial
(9)
capacity (peak shaving)
buildings (E)
Pre-
-15% to -35 %
Office building (S)
(10)
cooling
Reduced consumption at
-25% to -40%
Office building (S)
(9)
peak (load shifting)
Electricity cost savings
-40 %
Office building (S)
(10)
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
12 / 36
provide flexibility to the electricity grid – 20/10/2016
Based on this literature findings, there are
five important observations that can be made regarding the
potential for use of building thermal mass that resulted from the studies:
(i)
There is a lack of experimental studies on real buildings available in the scientific literature, as
most results have been based on simulations.
(ii)
Together with the available thermal storage capacity, the cost savings potential is very
sensitive to the insulation level, control strategy, heating system characteristics, price
incentives, and market set-up. In other words, there are some specific requirements that will
enable the utilization of the flexibility provided by the thermal mass to its full potential.
(iii)
There is a good potential for load-shifting and peak shaving when utilizing structural thermal
energy storage for pre-heating or pre-cooling (up to 50% under optimal circumstances) and
the associated cost savings can be significant (up to 40%)
(iv)
The global benefits in terms of RES penetration and CO2 emissions reduction can be quantified
when analysing the RES curtailment and peak generation that can be avoided through the
demand-response programs.
(v)
Load shifting can lead to an increase of the total electricity used by the heat pump because of
the storage losses.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
13 / 36
provide flexibility to the electricity grid – 20/10/2016
4
ANALYSIS OF FINDINGS
4.1 REQUIREMENTS
AND
FACILITATORS
Before analysing the identified benefits and limitations around the utilization of structural thermal energy
storage, this chapter discusses requirements and facilitators that are considered essential to tap
structural thermal energy storage potential. The thermal mass of building materials has been tapped by
building designers for ages and building users can benefit from the flexibility provided by the passive
thermal storage in some conditions without any specific design optimization or demand-response
strategy. Nevertheless, there are some specific requirements that will enable the active utilization of the
flex bility provided by structural thermal energy storage.
Thermal insulation
A performant insulation and ventilation system are a perquisite to guarantee an optimal thermal storage
efficiency for structural thermal storage (2), (11). Storing energy in the building material will always
induce passive thermal losses. In order to improve not only the energy efficiency of the building, but also
its structural thermal energy storage efficiency, the building envelope must be performant with adequate
thermal insulation and air-sealing in order to contain the thermal losses to the external environment to a
minimum. The total losses will also depend on the desired storage duration and the type of heating
system, as discussed later.
Sufficient fabric cover
When using heating or cooling systems integrated in a concrete slab (e.g. TABS), the heating/cooling
fluid and the ambient air are separated by a concrete cover. The thickness of this cover (and the resulting
thermal capacity that can be activated) plays an important role in the thermal storage duration: Increasing
the thickness of the cover will enable load shifting over longer durations for both heating and cooling
(12).
For example, a potential storage duration of about 10 hours has been tested for a concrete cover of 15
cm thick compared to a duration of 5 hours for a cover of 5 cm (12). This thickness can be an advantage
or a disadvantage depending on the load shifting strategy.
Suitable heating/cooling system
An electrical heating and/or cooling system is a perquisite to tap flexibility on the electricity market. This
will be materialized in an electricity driven heat pump. According to the European Heat Pump Association
(EHPA), more than 7 million heat pumps were already operating in Europe in 2014 and the market is
currently growing 10% annually. An expected increase in the penetration of energy efficient heat pump
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
14 / 36
provide flexibility to the electricity grid – 20/10/2016
systems for space heating will play an important role in the further electrification of the European energy
market. (2)
Outside the electricity market, demand-response programs are also explored in the context of district
heating systems. Local thermal storage and demand-side management are then proposed to increase
the performance of the district thermal system and increase the penetration of renewable production
sources (4).
Underfloor heating combined with available thermal mass for thermal storage show slightly higher
storage performances compared to radiator heated system. Simulations show that a median efficiency
value of 93 % is obtained for dwellings equipped with a radiator and 96 % for dwellings equipped with
floor heating system.
(2)
Smart control
In a smart grid context, the optimal utilization of structural thermal energy storage requires an optimization
of the control strategies with adequate building automation, such as a model predictive control (MPC).
This control adapts the heating and cooling by taking into account key parameters and their evolution in
the future: future heat/cold demand, internal and external gains, comfort requirements, prices incentives
for demand-response, storage capacity. This thus requires a communication channel between the
building and e.g. a cloud computing infrastructure (2).
Load aggregation framework
When evaluated on a stand-alone basis and as a single building, the energy and power advantage as a
result of operating a demand response strategy (kW or kWh) is insignificant when compared to grid-wide
system requirement (MW or GWh requirements). However, an aggregated community of buildings can
meet the requirements.
For example, a Dutch experiment (8) realised a cooling power peak shaving of up to 7 kW for a medium
size office building while the Dutch power systems guidelines require potential to deliver a minimum bid
of 1 MW, 4 MW and 20 MW for participation in power grid support services for primary-, secondary- and
tertiary- reserve respectively (13). Effective load aggregation framework for multiple buildings is therefore
required to participate in large demand side flexibility (DSF) schemes. On comparative scale, aggregation
of simultaneous cooling loads from hundreds to a few thousand similar buildings are required for
participation in provision of primary-, secondary- and tertiary- reserve respectively.
Aggregation of shiftable loads involving thousands of buildings is a challenge because of the
communication required, the number of factors, appliances, equipment and buildings. This challenge
should be solved with the recent and future developments in terms of building automation,
communication technology, distr buted control and micro-processor capabilities.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
15 / 36
provide flexibility to the electricity grid – 20/10/2016
Energy price incentive
Pre-heating and pre-cooling strategies are interesting when incentives are existing, e.g. when time-of-
use prices are low or when own renewable production is high. Energy cost savings cannot be realized
with demand response if the energy price is flat.
Under the current tariff structure applied for the majority of European consumers, the incentive is stil
limited compared to its potential. Currently, typical examples of situations with incentives for the operation
of a heat pump are: (i) at night when cheaper night tariff is available and (ii) on sunny days when
photovoltaic own production is in excess.
In the near future, the grid operator or electricity supplier can provide incentives to consumers such as
capacity tariffs and time-of-use prices that are reflecting the time-of-use grid congestion and the
production prices.
4.2 BENEFITS
Transmission and distribution infrastructure
Electricity demand-response programs have shown to have a positive impact on the electricity grid. They
reduce the required investment in the electricity grid capacity: by decreasing the grid congestion, peak
shaving defers costly investment in network reinforcement and increase long-term network reliability.
Stability issues on the distribution grid are also avoided and overall losses are reduced.
In case of district heating demand response program, similar benefits can be obtained on the pipeline
network: DSM can defer costly investments in additional distr bution capacity (14).
Investment cost savings
The reduction of heating or cooling peak load is considered to be one of the main benefits of a demand
response strategy using structural thermal mass since there is a significant potential for investments cost
savings at two levels. Both (i) the heating/cooling unit peak capacity requirement at building level and (ii)
the need for additional electricity peak production units at system level are lower, leading to economic
benefits.
Demand response using the structural thermal mass is able to reduce the required capacity on average
by 30%, by shifting the heat pump operation away from peak periods (2). Some tests on experimental
buildings have shown that there is a potential for load reduction of up to 50% in peak hours (9).
The economic benefit of peak shaving are estimated by assuming that the investment cost for a peak
power plant is 1250 €/kW instal ed capacity (i.e. for a combined cycle gas turbine). Assuming that the
avoided investment costs are shared among all the demand-response participants annually, with a plant
life time of 25 years and a discount rate of 3.5%, the cost saving per household fluctuates around € 300
per year, until 50% ADR penetration. Above this penetration level, the savings per participant decrease
since they are shared among a bigger number of participants (6).
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
16 / 36
provide flexibility to the electricity grid – 20/10/2016
Similar investment cost savings in installed capacity (close to 1000 €/kW) have been analysed for district
heating (14).
Operating cost savings
Opportunities for reducing operating costs through use of building thermal mass for heating or cooling
are due to four effects: (i) by replacing expensive on-peak electricity by cheaper off-peak electricity, (ii)
by participating in the reserve markets, (iii) by reducing mechanical cooling resulting from the use of cool
night-time air for ventilation precooling, and (iv) by improving efficiency with increasing operation at more
favourable part-load and ambient conditions. However, these benefits must be balanced with the
increased energy losses1 that occurs with pre-heating or pre-cooling of the thermal mass. The resulting
operating cost savings associated with load shifting and demand reductions depend upon both the
method of control and the specific application. (10)
In general, better opportunities for operating costs savings exist for higher ratios between on-peak and
off-peak rates and longer on-peak hours. However, the savings are more sensitive to the ratio of on-peak
to off-peak rates than to the length of the on-peak period. Cooling simulations tapping the optimal control
of the structural thermal energy storage have shown energy costs savings ranging from 0 to 35%
depending on utility rates (10). Similar electricity savings of 34% have been observed on an experimental
service building in Portugal following a pre-heating strategy to avoid consumption during peak-periods.
(5)
Several studies have also shown a clear correlation between the amounts of renewable energy produced
in the system (i.e. RES penetration) and the aforementioned operating costs savings potential (6), (7).
Higher RES penetration tends to make the electricity prices more volatile, increasing the ratio between
on-peak and off-peak rates and thus increasing the potential operating costs savings.
Higher RES pene
tration
The use of structural thermal energy storage has the potential to significantly increase the penetration of
renewable energy sources (RES) in the electricity production mix, mainly due to a reduction of the
curtailment losses (2), (5). Curtailment is a waste of renewable energy corresponding to a surplus of
renewable generation compared to the electricity demand. It mainly occurs during windy night in areas
with high wind energy penetration or during sunny days in areas with high photovoltaic penetration. Some
scientific studies have been able to quantify the potential increase of demand covered by RES with an
adapted pre-heating strategy using the structural thermal mass of the building.
For example, the use of structural thermal energy storage in Belgian dwellings could result in a 25%
increase in the fraction of the heat demand covered by RES. (2)
In a country with higher RES penetration like Portugal, recent studies have found that significant part of
the surplus renewable energy generated during night and early morning (19–30%) can potentially be
1 This increase in total energy requirements is discussed in chapter 4.3
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
17 / 36
provide flexibility to the electricity grid – 20/10/2016
absorbed by applying a pre-heating strategy. During the cooling period, a temporary shut-down of the
space conditioning can also substantially compensate the intermittences of wind power generation and
wind forecasting errors during the first hour of unbalance, giving enough time for the other resources of
the electrical system to adapt. (5)
This last finding is very promising for the European market since wind power already covers a significant
part of the demand for electricity in many areas of Europe. Wind power often presents large variations of
generation with extreme ramp rates and large forecasting errors and the wind generation exceeds the
electricity demand several times a year.
CO2 emission reduction
Due to the increased penetration of renewable energy sources and the reduction of the use of fossil fuel,
the introduction of heat pumps, replacing fossil fuel heating systems, combined with demand response
significantly affects the CO2-emissions.
Simulations on Belgian dwellings have shown that active demand response strategy using structural
thermal energy storage allows higher RES penetration (i.e. less curtailment) reducing the operation CO2
emissions by 15% on average. It was shown that the individual reduction per household was ranging
from 0.25 ton/year to 0.55 ton/year or from 6% to 25% depending on the building design and heating
system. The best results being obtained for buildings with floor heating and the best insulation (2).
Since heating or cooling during very cold or hot periods is often carried out with peak-load marginal
electricity generated with fossil fuel power plant, large reductions of CO2-emissions may also be obtained
by shaving those peaks tapping the storage potential of heavyweight buildings. For dwellings with floor
heating, simulations have demonstrated a potential to reduce 550 kWh peak electricity consumption from
gas-fired power plants per building per year (15). This electricity reduction roughly corresponds to a
reduction of 0.275 ton/year per household.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
18 / 36
provide flexibility to the electricity grid – 20/10/2016
4.3 LIMITATIONS
Energy consumption increase
In any kind of storage, one of the downsides is the global increase in the total energy consumption
because of the storage losses. On a building level, the consumption increase can be explained by higher
thermal losses that correspond to an increase in the indoor temperature when the building is pre-heated.
As discussed in paragraph 4.1, performant insulation is therefore essential to curb the losses that are
usually in a range of 1.5% - 7.5%. For example, pre-heating strategy in Belgian dwellings would
potentially increase the global electricity use of heat pumps by 5% on average (2). A less pronounced
consumption has been observed when the heat pump is combined with underfloor heating systems
compared to (low-temperature) radiators (15).
At country level in Belgium, the calculated absolute electricity demand increase would be in a range
between 20 to 150 GWh annually (6), a very limited amount compared to the total electricity demand of
about 88 TWh (0.02% to 0.17%).
One may argue that the benefits of thermal storage are wasted in higher thermal losses. To see whether
this is the case, the decrease in RES curtailment per building can be plotted against the increase in
electricity consumption per building.
Figure 4: Decrease in curtailing RES per building with respect to extra electricity consumption
per building when applying ADR. The figure shows that the decrease in RES curtailment is higher
than the extra electricity consumption for all the simulations. (15)
From the above figure, the decrease in curtailment is always higher (above the line) than the increase in
electricity consumption due to ADR. For example, applying active demand response causes a building
to consume 230 kWh additional electricity but reduces almost 600 kWh of RES curtailment, then on a
net basis, 370 kWh fossil fuel generation is saved. Hence on a net basis, less electricity from gas-fired
power plants is used.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
19 / 36
provide flexibility to the electricity grid – 20/10/2016
Limiting conditions
There are several limitations related to the range of utilization of structural thermal energy storage:
storage duration is limited in time and often limited to specific seasons.
A minimal duration of an ADR event exists and is specific to the design of the HVAC system. This
potentially limits the applicability of the proposed potential of flex bility to certain ADR market designs.
Also
a maximal duration of an ADR event should be considered. On the one hand, the maximal
duration is limited by the storage efficiency that significantly decreases with the flexibility event duration
(2). Above a certain duration and depending on the heating system, insulation and available thermal
mass, the thermal energy losses will be too high to be covered by the benefits in terms of cost savings
and RES penetration. One the other hand, the duration is also limited by the comfort limits as will be
discussed in the next chapter. With an estimation of about 2h storage for every 1°C of pre-cooling2 (10),
a comfort limit set to 4°C below the maximum temperature is limiting the pre-cooling duration to 8h.
There are also obvious
mid-seasonal limitations: the available structural storage capacity and its
efficiency significantly decreases with e.g. the decreasing heat demand (increasing outdoor temperatures
and solar gains). In mid-season and summer the potential for ADR by activating the structural storage
capacity using the heating system is marginal, due to low storage capacity and efficiency. For Northern
Europe countries, ADR using structural storage capacity for the heating systems can only be used
efficiently in winter. For Southern Europe countries, ADR using structural storage capacity for the cooling
systems can only be used efficiently in summer (2).
The impact of
self-consumption of the photovoltaic (PV) production is found to be limited for pre-
heating strategies because periods with high PV-production coincide with low heat demands, due to the
use of passive solar gains in the buildings. Consequently, the potential for load-shifting using the heating
system is limited when the target is to consume PV local production. (2)
Comfort
When using the structural thermal energy storage capacity, the indoor temperature is influenced by the
pre-heating/cooling strategy. This influence may not compromise thermal comfort and occupant
satisfaction.
This means that, on the one hand, the indoor temperature should for instance not increase more than
1.1°C in 0.25 h or 2.1°C in 1 h as described in ASHRAE Std. 55-2004, although higher values may be
allowed if this change is the result of control or adjustments by the user (2). On the other hand, absolute
comfort bands can be defined but strongly depend on the outdoor climatic conditions.
2 Typically, internal gains are on the order of 30 –70 W per square meter of floor space. The thermal capacity for typical concrete building
structures is on the order of 12– 24 Wh/°C/m². (10)
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
20 / 36
provide flexibility to the electricity grid – 20/10/2016
These requirements however do not necessarily limit the applicability of STES-based ADR. It has been
demonstrated that the associated operational benefits of flex bility can be grasped without compromising
stated local comfort bands (6). This includes examples of heavyweight buildings where the heating in
winter period remains out for up to 7 days before the heating reactivates to avoid going out of the comfort
band (16). Even more, the value of the additional available flexibility given by comfort temperatures
outside these bands can decrease because of lower storage efficiencies associated with higher
temperatures.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
21 / 36
provide flexibility to the electricity grid – 20/10/2016
4.4
IMPACT ON STAKEHOLDERS
The benefits and limitations are felt differently depending on the position of the stakeholders. The
following table summarizes the qualitative impact of ADR using structural thermal energy storage on
several stakeholders.
Table 2: Stakeholder table with the present and future qualitative impact of ADR on those
stakeholders
Stakeholder
Present
Future
Little incentive and see Demand
Baseload
Response (DR) only as a means
+/-
Idem
generators3
+/-
of hedging to unplanned
outages
Curtailment will be a growing
RES generators
+
ADR is very interesting to avoid
++
issue with increasing RES
curtailment
share
Peaking
generators4
-
See ADR as direct competition
--
Might poss bly disappear with
performant ADR
Transmission
ADR necessity shal increase
ADR facilitate supply and
since supply and demand
System Operators5
+
demand balance and improve
++
(TSO)
unbalance will be a growing
reliability
issue
ADR can be used to relieve
Distribution
network congestion and improve
Idem but with increasing
System Operators6
+
local reliability or quality of
++
challenges related to energy
(DSO)
supply and reduce network
transition
investments
ADR is interesting as a means
Energy retailers
to balance their contracted
+
+
Idem
supply with the demand of their
customers
ADR can be used to reduce the
operation costs. Incentives to
Building users
+/-
respond depends on the price
+
Price incentives shall be more
elaborated in the future
incentive offered by the retailer
or the DSO
Building owners
+
ADR targeting peak shaving can
+
Idem
decrease HP investment cost
3 Electricity producers that operate power plants consistently generating the electrical power needed to
satisfy minimum/base load demand.
4 Electricity producers that operate power plants generating the electrical power needed to satisfy peak
demand.
5 TSO: Operator that transmits electrical power from generation plants over the high- and medium
voltage electrical grid to regional or local electricity distribution system operators.
6 DSO: Operator that distributes electrical power from substations to the electricity consumers over
lower voltage electrical grid.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
22 / 36
provide flexibility to the electricity grid – 20/10/2016
5 POLICY
RECOMMANDATIONS
5.1 EPBD
REVISION
The review of the Energy Performance of Buildings Directive (EPBD) is an opportunity to raise ambitions
with regards to the exploitation of structural thermal storage to its full potential.
x
Evolve to new energy performance calculation models to take thermal energy storage into
account: Current energy performance calculation models that are based on a steady-state
analysis do not consider storage effects which are of value on a grid level, such as the storage and
release of thermal energy in the elements of the building. Dynamic calculation methods should be
preferred in order to allow designers to make thermal mass available in their energy management
strategy. Specifically for structural thermal energy storage, this requires the addition of the concept
of
active thermal capacity compared to the current definition of thermal capacity in the EPBD.
x
Insist on new energy performance calculation models to take into account the dynamic use
of thermal energy storage in a load shifting context: Given the stated dynamic calculation
methods which allow designers to make use of thermal mass in their energy management strategy;
the effective implementation of a storage-based ADR should be evaluated and rated.
x
Improve the recognition of the benefits of structural thermal energy storage by taking the
“available structural storage capacity” into account in the Directive: Thermal capacity is
presently recognised in the Directive as only contributing to the energy efficiency of buildings at
the same level as other solutions (i.e. insulation, heating and cooling systems, renewable energy)
while the available structural storage capacity is a key indicator for their ability to participate in ADR
in a smart grid context. The relation between buildings and the grid should be emphasized and
promoted in a dialog between all actors in the energy sector and building industry.
x
Promote the interoperability between building heating/cooling systems and the energy
market in order to deploy ADR: Aggregation of shiftable loads involving thousands of buildings
is a challenge because of the communication required, the number of factors, appliances,
equipment and buildings. This communication can occur through a supervisory and control and
data acquisition (SCADA) system for remote monitoring and control that operates with the grid and
market signals and insures the interoperability of a massive amount of buildings.
x
Encourage energy storage incentives in order to make it economically viable for end-users
today: In the near future, the grid operator or electricity supplier can provide incentives to
consumers such as time-of-use prices that are reflecting the time-of-use grid congestion in order
to encourage them in participating in balancing the grid.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
23 / 36
provide flexibility to the electricity grid – 20/10/2016
5.2 OTHER
RECOMMENDATIONS
The following policy recommendations would allow better use of the storage capacity but they are
considered to be out of the scope of the EPBD.
x
Encourage experimental studies / pilot projects in real buildings to demonstrate the benefits
of ADR using structural thermal energy storage in operation.
x
Encourage energy tariff structure reflecting the demand-supply unbalances in order to
provide an incentive for ADR.
x
Align storages regulatory frameworks in order to maximize the storage opportunities,
especially at peak.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
24 / 36
provide flexibility to the electricity grid – 20/10/2016
6 CONCLUSION
The literature provides several examples of the growing potential for flexibility using building loads that
can be shifted, like space heating and cooling. In a smart grid context, the structural thermal energy
storage capacity of heavyweight buildings have a promising potential for load shifting or peak shaving in
active demand response programs. Scientific studies demonstrated that pre-cooling strategies have a
potential to reduce a buildings electricity peak by up to 50% while the total energy costs can decrease
by 40% in best case. Some studies go further by translating those energy and cost savings into global
benefits such as renewable energy systems increase and associated CO2 emission reduction.
Nevertheless, it was emphasized that there are some
specific requirements enabling the utilization
of the flexibility provided by the thermal mass of a building to its ful potential. An efficient thermal
insulation is a basic requirement to avoid storage losses and to keep the structural thermal energy
storage efficiency within acceptable ranges. When using underfloor heating system or thermally activated
building systems, the fabric layer thickness is another important parameter to determine the duration of
the thermal storage. In order to access the flexibility market, the building also needs suitable heating and
cooling systems such as electrical heat pump or new generation district heating systems and a smart
controller using optimization strategies targeting the benefits. As an individual heating or cooling system
load is relatively small compared to the market needs, the load has to be aggregated e.g. in order to be
able to access the balancing market. The market should provide price incentives to the building user
such as time-of-use prices encouraging to consume electricity during off-peak period.
In a second step, the
main benefits of this flexibility have been further analysed. The positive impact
on the electricity grid is well known: Active demand response can reduce the required investment in the
electricity grid capacity, stability issues and overall losses. Also, the reduction of heating or cooling peak
load is considered to be one of the main benefits of a demand response strategy using structural thermal
mass since there is a significant potential for investments cost savings at two levels: (i) the
heating/cooling unit peak capacity requirement at building level and (ii) the need for additional electricity
peak production units at system level are lower, leading to economic benefits. Opportunities for operating
costs savings through use of building thermal mass for heating or cooling are also significant: (iii) by
replacing expensive on-peak electricity by cheaper off-peak electricity, (iv) by participating in the reserve
markets, (v) by reducing mechanical cooling resulting from the use of cool night-time air for ventilation
precooling, and (vi) by improving efficiency with increasing operation at more favourable part-load and
ambient conditions. Additionally, the use of structural thermal energy storage has the potential to
significantly increase the penetration of renewable energy sources in the electricity production mix,
mainly due to a reduction of the curtailment losses (i.e. due to an increase of up to 25% in the fraction of
the heat demand covered by renewable energy sources). Simulations have shown that this higher
renewable energy sources penetration could reduce the CO2 emissions related to the heating of buildings
by about 15%.
However, there are also
limitations associated with the implementation of pre-heating or pre-cooling
strategies. In any kind of storage, a downside is the global increase in the total energy use because of
the storage losses. On a building level, the consumption increase (+5% on average) can be explained
by higher thermal losses that correspond to an increase in the indoor temperature when the building is
pre-heated. One may argue that the benefits of thermal storage are counteracted with higher thermal
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
25 / 36
provide flexibility to the electricity grid – 20/10/2016
losses, but the increased use of renewable energy largely exceeds the consumption increase. Also
several limitations occur related to the range of utilization of structural thermal energy storage: the
storage duration is limited to design-specific time ranges and its profitability is often limited to pronounced
seasons (e.g. heating and cooling season). Lastly, the buildings thermal comfort and occupant
satisfaction may not be compromised by the fluctuations in indoor temperature induced by the pre-
heating (or pre-cooling) strategy.
Based on these findings, the capacity of heavyweight buildings to store energy in its structural elements
shows to be an important factor in the development of so-called
smart grids, providing the required
flex bility to increase further the penetration of renewable energy sources and reduce the CO2 emissions.
Building energy efficiency policies should therefore encourage the development of energy performance
calculation models which take into account structural thermal energy storage and its dynamic behaviour
in a context of automated demand response. The EPBD should improve the recognition of the benefits
of structural thermal storage by taking the “available structural thermal energy storage capacity” into
account. The utilization of optimal controlled strategies should also be promoted, as well as the
interoperability between the building control systems and the energy market. Lastly, energy storage
market incentives need to be further developed and harmonized to make it economically viable for end-
users. Those recommendations can foster the utilization of structural thermal energy storage which play
a significant role in the energy transition.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
26 / 36
provide flexibility to the electricity grid – 20/10/2016
7 ANNEXES
7.1 ABBREVIATIONS
ACHP
Air Conditioning Heat Pump
ADR
Active Demand Response
CEMBUREAU
The European Cement Associa ion
DR
Demand Response
DSF
Demand Side Flexibility
DSM
Demand Side Management
EED
Energy Efficiency Directive
EPBD
Energy Performance of Buildings Directive
EU
European Union
GCHP
Ground Coupled Heat Pump
HP
Heat Pump
MPC
Model Predic ive Control
nZEB
Nearly Zero Energy Buildings
RES
Renewable Energy Systems
SCADA
Supervisory Control and Data Acquisition
SRI
Smart Readiness Indicator
STES
Structural Thermal Energy Storage
TABS
Thermal Ac ivated Building Systems
TES
Thermal Energy Storage
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
27 / 36
provide flexibility to the electricity grid – 20/10/2016
7.2 GLOSSARY
x
Active thermal energy storage: TES based on a control system to administer the heat charging and
discharging.
x
Available structural storage capacity for active demand response [kWh]: the amount of heat that
can be added to the structural mass of a building, without jeopardising thermal comfort, in the time-
frame of an ADR-event and given the dynamic boundary conditions.
x
Demand response: The ability to shift energy demand by reducing peak consumption and avoiding
grid imbalance.
x
Demand Side Management: DSM is inclusive of all undertakings on the demand side of an energy
system undertaken in close collaboration of the consumers and power system utilities in efforts to
alter load pattern using incentives, subsidies or cash benefits.
x
Flexibility: the ability to cost effectively balance electricity supply and demand continually while also
maintaining acceptable service quality to connected loads. This is inclusive of the ability for
periodic energy availability to the grid over a defined time, response to random unscheduled load
and provision of additional reserves to manage uncertainties arising from inaccurate forecasting or
sudden change in the weather.
x
Heavyweight building: construction made of loadbearing elements mainly composed with
heavyweight materials such as reinforced concrete, concrete masonry, stone, bricks or rammed
earth. Those heavyweight materials mostly have a high thermal mass compared to other materials.
x
Passive thermal energy storage: means that building parts with high heat capacity can absorb and
emit heat when the temperature in the environment changes. This is a phenomenon that always
takes place, even if no direct actions are carried out to utilize it at its full capacity.
x
Power shifting capability [s]: the duration during which a change in heating/cooling power can be
maintained, given the dynamic boundary conditions and the current state of charge, before the
comfort requirements are jeopardized.
x
Primary Energy: energy from renewable and non-renewable sources which has not undergone any
conversion or transformation process
x
RES Curtailment: Temporary reduction of renewable energy generation due to a shortage of
electricity demand or because the supplied power exceeds the grid capacity.
x
Smart Grid: upgradable electricity network that is enabled for intelligent control and multi-directional
communication between sources, loads and components in such a manner that allows for
cooperative and economical energy utilization.
x
State of charge: the fraction of the energy content of the storage medium at time t compared to the
total storage capacity.
x
Storage efficiency: the fraction of the heat that is stored during the ADR-event that can be used
subsequently to reduce the heating/cooling power needed to maintain thermal comfort.
x
Structural thermal energy storage (STES): TES using building materials as storage medium.
x
Thermal capacity: Terminology used in the EPBD recast Directive 2010/31/EU of the European
Parliament and of the Council of 19 May 2010 on the performance of buildings. Regulation No
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
28 / 36
provide flexibility to the electricity grid – 20/10/2016
244/2012 supplementing this directive denotes 'thermal capacity per unit area' measured in units
of J/(m²K) and to be evaluated according to EN ISO 137867
x
Thermal energy storage (TES): Any technology that stocks thermal energy by heating or cooling a
storage medium so that the stored energy can be used at a later time for heating and cooling
applications.
x
Thermal inertia: Commonly used for modelling thermal transfers properties of a material, defined
as the square root of the product of the material's bu k thermal conductivity and volumetric heat
capacity.
x
Thermal mass: One or multiple elements in the building with a significant amount of ‘thermal
capacity' able to store thermal energy in a building.
7 ISO 13786:2007 - Thermal performance of building components -- Dynamic thermal characteristics --
Calculation methods.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
29 / 36
provide flexibility to the electricity grid – 20/10/2016
7.3 BIBLIOGRAPHY
1.
BPIE. Smart Buildings in a Decarbonised Energy System. 2016.
2.
Reynders. Quantifying the impact of building design on the potential of structural storage for active
demand response in residential buildings. 2015.
3.
European Union. DIRECTIVE 2010/31/EU OF THE EUROPEAN PARLIAMENT AND OF THE
COUNCIL of 19 May 2010 on the energy performance of buildings. 2010.
4.
Lund H., Werner S. , Wiltshire R., Svendsen S., Thorsen J. E., Hvelplund F., and Mathiesen B.
V. 4th Generation District Heating (4GDH). Integrating smart thermal grids into future sustainable
energy systems. 2014.
5.
Carvalho A.D., Moura P., Vaz G.c., Almeida A.T. Ground source heat pumps as high efficient
solutions for building space conditioning and for integration in smart grids. 2015.
6.
Arteconi A., Patteeuw D., Bruninx K., Delarue E., D'haeseleer W., Helsen L. Active demand
response with electric heating systems: impact of market penetration. 2016.
7.
Patteeuw D., Henze G., Helsen L. Comparison of load shifting incentives for low-energy buildings
with heat pumps to attain grid flexibility benefits. 2016.
8.
Aduda KO, Labeodan T, Zeiler W, Boxem G, Zhao Y. Demand side flexibility: Potentials and
building performance implications. 2016.
9.
Xu, P. Evaluation of Demand Shifting with Thermal Mass in Two Large Commercial Buildings. 2006.
10.
Braun, James E. Load Control Using Building Thermal Mass. 2003.
11.
Karlsson. Possibilities of using thermal mass in buildings to save energy, cut power consumption
peaks and increase the thermal comfort. 2012.
12.
BMVIT. Energiespeicher Beton. 2016.
13.
50Hertz TRransmission Gmbh, Amprion Gmbh, Elia System Operator nv, Tennet TSOB. V.,
Tennet TSO Gmbh, Transnetbw mbh. Potential Cross-Border Balancing Cooperation Between the
Belgian, Dutch and German Electricity Transmission System Operators. 2014.
14.
IEA. Dynamic Heat Storage Optimisation and Demand Side Management. 2005.
15.
Patteeuw D., Reynders G., Bruninx K., Protopapadaki C., Delarue E., D'haeseleer W., Saelens
D., Helsen L. CO2-abatement cost of residential heat pumps with Active Demand. Response: demand-
and supply-side effects. 2015.
16.
Handler, Simon. Konditionierung von massiven Einfamilienhäusern mit Wärmepumpe unter
Nutzung der Leistungsspitzen im öffentlichen Stromnetz. 2016.
17.
European Concrete Platform. Concrete for energy-efficient buildings - The benefits of thermal
mass. 2007.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
30 / 36
provide flexibility to the electricity grid – 20/10/2016
18.
Cerbof. Energy saving through the utilization of the thermal behaviour of heavy buildings, based on
new materials, building frameworks and heat storage systems. 2012.
19.
Association of the Austrian Cement Industry. Heating, Cooling and Storage of Energy with
Concrete. 2015.
20.
European Union. DIRECTIVE 2012/27/EU OF THE EUROPEAN PARLIAMENT AND OF THE
COUNCIL of 25 October 2012 on energy efficiency, amending Directives 2009/125/EC and
2010/30/EU and repealing Directives 2004/8/EC and 2006/32/EC. 2012.
21.
CEMENTA. Conclusions of CEMBUREAU workshop on Thermal mass. 2016.
22.
BMVIT. Thermische Bauteilaktivierung. Entwicklungeines Rechenkerns. 2014.
23.
Austrian Institute of Technology. Demand Side Management in District Heating Networks. 2013.
24.
Michiorri A, Pelaez M, Dentel A, Buderus J, Bessa R, GouveiaC , Urteaga L, Rautiainen T.
Energy storage domain roles & classification. 2015.
25.
Saelens D., Parys W., Baetens R. Energy and comfort performance of thermally activated building
systems including occupant behavior. 2010.
26.
Braun J.E., Lawrence T.M., Klaasen C.J., House J. Demonstration of Load Shifting and Peak
Load Reduction with Control of Building Thermal Mass. 2004.
27.
Olsson Ingvarson, Werner. Building Mass used as short therm heat storage. 2008.
28.
Patteeuw D., Bruninx K., Arteconi A., Delarue E., D'haeseleer W., Helsen L. Integrated
modeling of active demand response with electric heating systems coupled to thermal energy storage.
2015.
29.
Deconinck. Rule-based demand side management of domestic hot water production with heat
pumps in zero energy neighbourhoods. 2013.
30.
Reynders. A GENERIC QUANTIFICATION METHOD FOR THE ACTIVE DEMAND RESPONSE
POTENTIAL OF STRUCTURAL STORAGE IN BUILDINGS. 2015.
31.
Karlsson. A conceptual model made in matlab that simulates the differences between heavy and
light structures in the field of energy, comfort and power demands. 2011.
32.
Verhelst. Model Predictive Control of Ground Coupled Heat Pump Systems for Office Buildings.
2012.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
31 / 36
provide flexibility to the electricity grid – 20/10/2016
7.4
TWO PRACTICAL EXAMPLES
7.4.1 Example
1
– “Low tech” - Office building with cooling chiller
This example is an office building with a typical heavyweight building structure such as concrete providing
a significant thermal energy storage capacity. The heating source is a gas boiler and the cooling occurs
through chillers. Both heating and cooling distribution system are connected to local fan coil units.
Because of those simple devices, this example is named “low tech” although a smart building controller
has been installed in order to optimize the building control including possible pre-heating and pre-cooling
strategies.
Figure 5: Schematic system description of Example 1
Because of large solar gains through wide windows and the significant internal thermal gains related to
office spaces (mostly computers and users), the building requires cooling during the summer in order to
avoid overheating. This cooling has a significant impact on the electricity bill when it is operated during
the day. However, there is a price incentive to pre-cool the building during the night when electricity rates
are lower than the day rates. At night, the electricity needed for circulators and the chiller can be
purchased at lower tariffs. In the case of cooling, the air cooled in the fan coil circulates in the room and
cools down the thermal mass of the building. By this means cooling is “stored” in the building structure.
During daytime, the thermal mass of the building absorbs internal and external heat gains. In many cases,
the cooled down building structure is able to avoid active cooling until noon. The operative temperature
raises, and when it reaches the upper boundary of the comfort range, the cooling system is activated.
The sizing of the production units can be limited because of the peak-shaving effect the precooling
enhances.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
32 / 36
provide flexibility to the electricity grid – 20/10/2016
Figure 6: Conceptual daily power and temperature profiles of Example 1. Here, Top indicates the
operative temperature with the comfort boundaries indicated with dashed lines, while PHP denotes
the power consumption of the chiller.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
33 / 36
provide flexibility to the electricity grid – 20/10/2016
7.4.2 Example
2
– “High tech” – Office building with heat pump and TABS
This example is a modern office building with a concrete building structure providing a significant thermal
energy storage capacity. The concrete slabs are including a Thermally Activated Building System (TABS)
that acts as a heating and cooling distr bution system. The heating and cooling source is a geothermal
heat pump. The cooling can be passive (geothermal passive cooling with a circulator) or active
(geothermal active cooling using the heat pump and the circulator). Because of those more advanced
devices, this example is named “high tech”. A smart building controller has also been installed in order
to optimize the building control including possible pre-heating and pre-cooling strategies.
Figure 7: Schematic system description of Example 2
In this example, there is a large amount of electricity produced intermittently by wind turbines. During the
periods with high wind production, there is an incentive to pre-cool the building in order to tap lower
electricity tariffs. The cooling production system can follow the production of wind energy. During periods
of high green electricity yield, the system will “charge” the TABS. In the case of cooling, it will drop the
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
34 / 36
provide flexibility to the electricity grid – 20/10/2016
surface temperature till +/- 22°C8. This means that the concrete slabs have a lower inside temperature
and will be able to provide a lot of cooling the next day. During daytime, the thermal mass of the building
absorbs internal and external heat gains. The heat pump is not active. Green electricity can be used for
other purposes such as office equipment, ventilation, lighting, etc. The operative temperature raises, but
does not exceed the upper part of the allowed temperature range.
Figure 8: Conceptual daily power- and temperature profiles of Example 2. Here, Top indicates the
operative temperature with the comfort boundaries indicated with dashed lines, while PHP denotes
the power consumption of the chiller.
8 The surface temperature should always by higher than the dew point temperature. 20…22°C is a safe
temperature in dry and moderate climates.
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
35 / 36
provide flexibility to the electricity grid – 20/10/2016
QUALITY INFORMATION
13/10/2016
20/10/2016
Template V. 15
Structural thermal energy storage in heavy weight buildings – Analysis and recommendations to
FINAL VERSION
36 / 36
provide flexibility to the electricity grid – 20/10/2016
