ENV 12977-3:2001

SLOVENSKI STANDARD
01-november-2002
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Thermal solar systems and components - Custom built systems - Part 3: Performance
characterisation of stores for solar heating systems
Thermische Solaranlagen und ihre Bauteile - Kundenspezifisch gefertigte Anlagen - Teil
3: Leistunsprüfung von Warmwasserspeichern für Solaranlagen
Installations solaires thermiques et leur composants - Installations assemblées a façon -
Partie 3: Caractérisation des performances des dispositifs de stockage pour des
installations de chauffage solaire
Ta slovenski standard je istoveten z: ENV 12977-3:2001
ICS:
27.160 6RQþQDHQHUJLMD Solar energy engineering
91.140.10 Sistemi centralnega Central heating systems
ogrevanja
91.140.65 Oprema za ogrevanje vode Water heating equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN PRESTANDARD
ENV 12977-3
PRÉNORME EUROPÉENNE
EUROPÄISCHE VORNORM
April 2001
ICS 27.160; 91.140.10; 91.140.65
English version
Thermal solar systems and components - Custom built systems
- Part 3: Performance characterisation of stores for solar heating
systems
Installations solaires thermiques et leur composants - Thermische Solaranlagen und ihre Bauteile -
Installations assemblées à façon - Partie 3: Caractérisation Kundenspezifisch gefertigte Anlagen - Teil 3:
des performances des dispositifs de stockage pour des Leistunsprüfung von Warmwasserspeichern für
installations de chauffage solaire Solaranlagen
This European Prestandard (ENV) was approved by CEN on 12 March 2001 as a prospective standard for provisional application.
The period of validity of this ENV is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the ENV can be converted into a European Standard.
CEN members are required to announce the existence of this ENV in the same way as for an EN and to make the ENV available promptly
at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the ENV) until the final
decision about the possible conversion of the ENV into an EN is reached.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2001 CEN All rights of exploitation in any form and by any means reserved Ref. No. ENV 12977-3:2001 E
worldwide for CEN national Members.

Page 2
Contents
Page
Foreword . 3
Introduction. 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Symbols and abbreviations . 10
5 Store classification. 11
6 Laboratory store testing. 11
7 Store test combined with a system test according to ISO 9459-5 . 51
8 Test report . 51
Annex A (normative) Requirements for the numerical store model . 54
Annex B (normative) Store model benchmark tests . 56
Annex C (normative) Benchmarks for the parameter identification . 58
Bibliography. 60

Page 3
Foreword
This European Prestandard has been prepared by Technical Committee CEN/TC 312
"Thermal solar systems and components", the secretariat of which is held by ELOT.
According to the CEN/CENELEC Internal Regulations, the national standards
organizations of the following countries are bound to announce this European
Prestandard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany,
Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain,
Sweden, Switzerland and the United Kingdom.
The annexes A, B and C are normative.
Introduction
The test methods for stores of solar heating systems as described in this Prestandard
are required for the determination of the thermal performance of small custom built
systems as specified in ENV 12977-1.
These test methods deliver parameters, which are needed for the simulation of the
thermal behaviour of a store being part of a small custom built system.
NOTE 1 For additional information about the test methods for the performance characterization of
stores see
1 in Bibliography.
NOTE 2 With the test methods for stores given in prEN 12897:1997 only a few parameters are
determined in order to characterise the thermal behaviour of a store. These few parameters are not
sufficient for the determination of the thermal performance of small custom built systems as described in
ENV 12977-2.
This is due to the fact that the performance of thermal solar systems depends much more on the
thermal behaviour of the store (e. g. stratification, heat losses), as conventional systems do. Hence this
separate Prestandard for the performance characterisation of stores for solar heating systems is
needed.
Page 4
1 Scope
This Prestandard specifies test methods for the performance characterization of
stores which are intended for use in small custom built systems as specified in
ENV 12977-1.
Stores tested according to this Prestandard are commonly used in solar hot water
systems. However, also the thermal performance of all other thermal stores with water
as storage medium (e.g. for heat pump systems) can be assessed according to this
Prestandard.
The Prestandard applies to stores with a nominal volume between 50 and 3000 litres
and without integrated oil or gas burner.
2 Normative references
This European Prestandard incorporates, by dated or undated reference, provisions
from other publications. These normative references are cited at the appropriate
places in the text and the publications are listed hereafter. For dated references,
subsequent amendments to or revisions of any of these publications apply to this
European Prestandard only when incorporated in it by amendment or revision. For
undated references the latest edition of the publication referred to applies.
EN 12976-2:2000 Thermal solar systems and components - Factory made
systems - Test Methods
ENV 12977-2:2001 Thermal Solar Systems and Components – Custom Built
Systems – Test Methods
prEN 12828:1997 Heating systems in buildings – Design and installation of water
heating systems
prEN 12897:1997 Water supply – Specification for indirectly heated unvented
(closed) hot water storage systems
EN ISO 9488 Solar energy – Vocabulary (ISO 9488:1999)
ISO 9459-5 Solar heating – Domestic water heating systems – Part 5:
System performance characterization by means of whole –
system tests and computer simulation
3 Terms and definitions
For the purposes of this European Prestandard the following terms and definitions together
with EN ISO 9488 apply.
3.1
ambient temperature
mean value of the temperature of the air surrounding the store
3.2
charge
process of transferring energy into the store by means of an heat source

Page 5
3.3
charge connection
pipe connection used for charging the storage device
3.4
combistore
store used for both domestic hot water preparation and space heating
3.5
~

constant inlet temperature ( )
x,i
temperature which is achieved during charge (x=C) or discharge (x=D), if the mean
~

value over the period of 0,5 reduced charge / discharge volumes (see 3.34) is within
x,i
~
o
(  1) C

x,i
3.6
~


constant flow rate (V )
~


flow rate which is achieved, when the mean value V over the period of 0,5 reduced charge
~


/ discharge volumes (see 3.34) is within V 10 %
3.7
~
constant charge power (P )
C
charge power which is achieved, when the mean value P over the period of 0,5 reduced
C
~
charge volumes is within P  10 %
C
3.8
conditioning
process of creating a uniform temperature inside the store by
~
o
discharging the store with  = 20 C until a steady state is reached
D,i
NOTE The conditioning at the beginning of a test sequence is intended to provide a well defined
initial system state, i. e. an uniform temperature in the entire store.
3.9
discharge connection
pipe connection used for discharging the storage device
3.10
dead volume / dead capacity
the volume / capacity of the store which is only heated due to heat conduction (e. g.
below a heat exchanger)
Page 6
3.11
direct charge / discharge
transfer or removal of thermal energy in or out of the store, by directly exchanging the
fluid in the store
3.12
discharge
process of decreasing thermal energy inside the store caused by the hot water load
3.13
double port
a corresponding pair of inlet and outlet connections for direct charge / discharge of the
store
NOTE Often, the store is charged or discharged via closed or open loops that are
connected to the store through double ports.
3.14
effective volume / effective capacity
the volume / capacity which is involved in the heat storing process if the store is
operated in a usual way
3.15
electrical (auxiliary) heating
electrical heating element immersed into the store
3.16
external auxiliary heating
auxiliary heating device located outside the store. The heat is transferred to the store
by direct or indirect charging via a charge loop. The external auxiliary heating is not
considered as part of the store under test
3.17
( )
heat loss capacity rate UA
s,a
the overall heat loss of the entire storage device per K temperature difference
between the store temperature and the ambient air temperature
NOTE The heat loss capacity rate depends on the flow conditions inside the store. Hence a
stand-by heat loss capacity rate and a operating heat loss capacity rate are defined. If (UA) is
s,a
mentioned without specification, (UA) represents the stand-by heat loss capacity rate.
s,a
3.18
heat transfer capacity rate
the thermal power transferred per K temperature difference

Page 7
3.19
immersed heat exchanger
heat exchanger which is completely surrounded with the fluid in the store tank
3.20
indirect charge / discharge
transfer or removal of thermal energy into or out of the store, via a heat exchanger
3.21
load
the heat output of the store during discharge. The load is defined as the product of the
mass, specific thermal capacity and temperature increase of the water as it passes
the solar hot water system
3.22
mantle heat exchanger
heat exchanger mounted to the store in a way, that it forms a layer between the fluid
in the store tank and ambient
3.23
measured store heat capacity
the measured difference in energy of the store between two steady states on different
temperature levels, divided by the temperature difference between this two steady
states
3.24
measured energy (Q )
x,m
time integral of the measured power over one or more test sequences, excluding time
periods used for conditioning at the beginning of the test sequences
3.25
measured power (P )
x,m
power calculated from measured volume flow rate as well as measured inlet and outlet
temperature
3.26
mixed
state when the local store temperature is not a function of the vertical store height
3.27
model parameter
parameter used for quantification of a physical effect, if this physical effect is
implemented in a mathematical model in a way which is not analogous to its

Page 8
appearance in reality, or if several physical effects are lumped in the model (e. g. a
stratification number)
3.28


nominal flow rate ( V )
n
the nominal volume of the entire store divided by 1 h
3.29
nominal heating power (P )
n
the nominal volume of the entire store multiplied by 10 W/l
3.30
nominal volume (V )
n
fluid volume of the store as specified by the manufacturer
3.31
operating heat loss capacity rate (UA)
op,s,a
heat loss capacity rate of the store during charge or discharge
3.32
predicted energy (Q )
x,p
time integral of the predicted power over one or more test sequences, excluding time
periods used for conditioning at the beginning of the test sequences
3.33
predicted power (P )
x,p
power calculated from measured volume flow rate, as well as measured inlet
temperature and calculated outlet temperature. The outlet temperature is predicted by
numerical simulation
3.34
reduced charge / discharge volume
integral of a charge / discharge flow rate divided by the store volume
3.35
stand-by
state of operation in which no energy is deliberately transferred to or removed from the
store
3.36
stand-by heat loss capacity rate (UA)
sb,s,a
heat loss capacity rate of the store during stand-by

Page 9
3.37
steady state
state of operation at which at charge or discharge during 0,5 reduced charge /
discharge volume (see 3.34) the standard deviation of the temperature difference,
between store inlet and store outlet temperature of the charging / discharging circuit is
lower than 0,05 K
NOTE In cases of an isothermal charged store rather constant temperature differences
between the inlet and outlet temperature of the discharge circuit may occur during the discharge of the
first store volume before the outlet temperature drops rapidly. These state is not considered as steady
state.
3.38
store temperature
temperature of the store medium
3.39
stratified
state when thermal stratification is inside the store
3.40
stratified charging
increase of thermal stratification in the store during charging
3.41
stratifier
device that enables stratified charging of the store. Common used stratifiers are e.g.
convection chimneys or pipes with radial holes
3.42
theoretical store heat capacity

the sum over all thermal capacities m  c of the entire store (fluid, tank material,
i p,i
heat exchangers) having part of the heat store process
3.43
thermal stratification
state when the local store temperature is a function of the vertical store height, with
the temperature decreasing from top to bottom
3.44
transfer time (t )
x,f
time period during which energy is transferred through the connections for charge
(x=C) or discharge (x=D). The transfer time is calculated over one or more test
sequences, excluding time periods used for conditioning at the beginning of the test
sequences
Page 10
4 Symbols and abbreviations
C thermal capacity of the entire store, in J/K
s
c specific heat capacity, in J/(kg K)
p
P nominal heating power, in W
n
P measured power transferred through the charge (x=C) or discharge (x=D)
x,m
circuit, in W
P predicted power transferred through the charge (x=C) or discharge (x=D)
x,p
circuit, in W
Q measured energy transferred through the charge (x=C) or discharge (x=D)
x,m
circuit, in J
Q predicted energy transferred through the charge (x=C) or discharge (x=D)
x,p
circuit, in J
t time required to achieve a steady state, in s
st
t transfer time for charging (x=C) or discharging (x=D) , in s
x,f
o

ambient temperature, in C
a
o

store temperature, in C
s
 o

inlet temperature of the charge (x=C) or discharge (x=D) circuit, in C
x,i

constant inlet temperature of the charge (x=C) or discharge (x=D) circuit, in
x,i
o
C
o

outlet temperature of the charge (x=C) or discharge (x=D) circuit, in C
x,o
(UA) heat transfer capacity rate between heat exchanger and store, in W/K
hx,s
(UA) heat loss capacity rate of the store, in W/K
s,a
(UA) operating heat loss capacity rate of the store, in W/K
op,s,a
(UA) stand-by heat loss capacity rate of the store, in W/K
sb,s,a
V nominal volume of the store, in l
n


V nominal flow rate, in l/h
n
~


V constant flow rate of the charge (x=C) or discharge (x=D) circuit, in l/h
x

mean logarithmic temperature difference, in K
m
 relative error in mean power transferred during charge (x=C) or discharge
x,P
(x=D), in %
 relative error in energy transferred during charge (x=C) or
x,Q
discharge (x=D), in %
 density, in kg/m
Page 11
5 Store classification
Hot water stores are classified by distinction between different charge and discharge
modes. Five groups are defined as shown in Table 1.
Table 1 - Classification of the stores
Group charge mode discharge mode
1 direct direct
2 indirect direct
3 direct indirect
4 indirect indirect
5 stores that cannot be assigned to groups 1 to 4
NOTE 1 All stores may have one or more additional electrical heating elements.
NOTE 2 Stores that can be charged or discharged directly and indirectly (e. g. a store of a
space heating system with an internal heat exchanger for the preparation of domestic hot water) can
belong to more than one group. In this case the appropriate test procedures or the assignment to one of
the groups respectively, shall be chosen depending on its mode of operation.
6 Laboratory store testing
6.1 Requirements on the testing stand
6.1.1 General
The hot water store shall be tested separately from the whole solar system on a store
testing stand.
The testing stand configuration shall be determined by the classification of hot water
stores as described in clause 5.
An example of a representative hydraulic testing stand configuration is shown in
Figure 1 and Figure 2.
The circuits are intended to simulate the charge and discharge loop of the solar
system and to provide fluid flow with a constant or well controlled temperature. The full
test stand consists of one charge and one discharge circuit.
NOTE 1 If the store consists of more than one charge or discharge devices (e.g. two heat
exchangers), then these are tested separately.

Page 12
The testing stand shall be located in an air-conditioned room where the room
o
temperature of 20 C should not vary more than 1 K during the test.

Both circuits shall fulfil the following requirements:
- The flow rate shall be adjustable between 0,05 m³/h and 3 m /h, by deviation < 2 %.
- The working temperature range shall be between 10 °C and 90 °C.
- The minimum heating power of the charge circuit shall be 15 kW.
- The minimum cooling power in the discharge circuit shall be 5 kW at a fluid
temperature of 20 °C.
NOTE 2 If mains water at a constant pressure and a constant temperature below 20 °C is
available, it is recommended to design the discharge circuit in a way, that it can be operated as closed
loop or as open loop using mains water to discharge the store.
- The minimum heating power of the discharge circuit shall be 5 kW.
- The control deviation of the store inlet temperature shall be less than 0,05 K.
- The minimum heating up rate of the charge circuit with disconnected store shall be
3 K/min.
- The minimum available electrical heating power for electrical auxiliary heaters shall
be 6,0 kW.
NOTE 3 The electrical power of the pump (P102) shall be chosen in such a way that the
temperature increase induced by the pump (P102) is less than 0,6 K/h when the charge circuit is "short
circuited" and operated at room temperature. (“short circuited” means that no storage device is
connected and SV102, V113, V115 and V116 are closed, see Figure 1).

Page 13
ST Store
Key
SV Solenoid valve
FF Flow meter
TT Temperature sensor
HX Heat exchanger
TIC Temperature indicator and controller
OP Overheating protection
VValve
PPump
Figure 1 - Charge circuit of the store testing stand

Page 14
The heating medium water in the charge circuit (see Figure 1) is pumped through the
cooler (HX101) and the temperature controlled heaters (TIC106) by the pump (P101).
A buffer tank (ST101) is used to balance the remaining control deviations. By means
of the bypass (V107) the flow through the store can be regulated, it also ensures a
continuously high flow through the heating section and therefore good control
characteristics. With the solenoid valve (SV101) the heating medium can bypass the
store to prepare a sudden increase of the inlet temperature into the store.
The temperature sensors are placed near the inlet (TT101) and outlet (TT102)
connections of the store, the connection to the store is established through insulated
flexible pipes.
The charge circuit can be operated closed, under pressure (design pressure 2,5 bar,
membrane pressure expansion tank and pressure relief valve (V109)) as well as open
(valve (V108) open) with the tank (ST102) serving as an expansion tank. A calibration
of the installed flow meter (FF105) is possible by weighing the mass of water leaving
the valve (V112). The installation is equipped with the usual safety devices, i. e.
pressure relief valve (V117) and overheating protection device (OP101).
The discharge circuit (see Figure 2) is constructed in a similar way. It includes two
coolers - (HX201) and (HX202) - and a temperature controlled heating element
(TIC206) with 5 kW heating power. The discharge circuit can either be operated in
open circulation with water from the net or it can be operated in closed circulation.
During open operation the water is led via the safety equipment (V201) and flows
through the coolers, the heating section and the flow meter (FF205) into the store. The
hot water leaving the store flows through the solenoid valve (SV201) and the valve
(V210) into the drain. The valve (V212) is closed.
For heating the water it is recommended to increase the flow through the heating
section with the pump (P201) in order to improve the control performance; the
additional volume flow returns through the bypass (V209).
During closed-circle operation, the valve of the safety equipment and the cut-off valve
(V210) remain closed, the valve (V212) is open and the water is circulated by the
pump (P201).
NOTE 4 For periodical checks of the measuring accuracy, it is recommended to integrate a
reference heater into the testing stand. Instead of a store, this reference heater is connected to the
testing stand. The reference heater is supplied with an electric heating device.
NOTE 5 See /2/ and /3/ in Bibliography for further information on the use of reference heaters.
The heat transfer fluid used for testing may be water or a fluid recommended by the
manufacturer. The specific heat capacity and density of the fluid used, shall be known
with an accuracy of 1 % within the range of the fluid temperatures occuring during the
tests.
Page 15
SV Solenoid valve
Key
TT Temperature sensor
FF Flow meter
TIC Temperature indicator and controller
HX Heat exchanger
VValve
PPump
Figure 2 - Discharge circuit of the store testing stand

Page 16
6.1.2 Measuring data and measuring procedure
The data listed in Table 2 shall be measured with the given accuracy:
Table 2 - Measuring data
Measuring data Measuring device Uncertainty
(see figure 1 and 2)


volume flow V in the charge circuit
FF105 2,0 %
C
between 0,05 m³/h and 1 m /h


volume flow V in the discharge circuit
FF205 2,0 %
D
between 0,05 m³/h and 1 m /h
temperature
of the charging medium
TT101 0,1 K
C,i
at store inlet
temperature
of the charging medium
TT102 0,1 K
C,o
at store outlet
difference in the charging medium
TT101 and TT102 0,02 K
temperature 
between store inlet
C
and store outlet:
(for tests according to 6.3.1)
difference in the charging medium
TT101 and TT102 0,05 K
temperature 
between store inlet
C
and store outlet:
(for tests according to 6.3.2)
temperature
of the discharging
TT201 0,1 K
D,i
medium at store inlet
temperature
of the discharging
TT202 0,1 K
D,o
medium at store outlet
difference in the discharging medium
TT201 and TT202 0,02 K
temperature 
between store inlet
D
and store outlet:
(for tests according to 6.3.1)
difference in the discharging medium
TT201 and TT202 0,05 K
temperature 
between store inlet
D
and store outlet:
(for tests according to 6.3.2)
ambient temperature
TT001 0,1 K
am


electric power Q (auxiliary heating)
-2 %
el
Page 17
The relevant data shall be measured every 10 s at least and the measured data shall
be recorded as mean values of at most three measured values. However, for Test H
(see 6.3.1.1.3) during the transient the temperatures shall be measured and recorded
every second.
The temperature sensors shall have a relaxation time of less than 10 seconds. (i. e.
90 % of the temperature variation is detected by the sensor immersed in the heat
transfer fluid within 10 seconds after an abrupt step in the fluid temperature).
Prior to each store test a zero measurement should be performed where the fluid in
the charge or discharge circuit is pumped over the short-circuited charge or discharge
circuit. “Short- circuited” means that flow pipe and return pipe of the corresponding
circuits are directly connected (recommended volume flow approximately 0,6 m /h,
temperatures 20 °C, 40 °C, 60 °C, 80 °C). If the measured temperature difference
exceeds the permissible uncertainty of 0,02 K / 0,05 K, the temperature sensors shall
be calibrated.
A reference heater may also be used for the zero measurement.

Page 18
6.2 Installation of the store
6.2.1 Mounting
The store shall be mounted on the testing stand according to the manufacturer's
instructions.
The temperature sensors used for measuring the inlet and outlet temperatures of the
fluid used for charging and discharging the storage device, shall be placed as near as
possible at least 200 mm to the inlet and outlet connections of the storage device. The
installation of the temperature sensors inside the pipes shall be done according to
approved methods of measuring temperatures.
If there is/are more than one pair of charging and/or discharging inlet or outlet
connections, then only one may be connected to the testing stand (at the same time)
while the other(s) shall be closed.
The pipes between the store and the temperature sensors shall be insulated
according to prEN 12828:1997.
6.2.2 Connection
The way of connecting the storage device to the testing stand depends on the
purpose of the thermal tests which shall be performed. Detailed instructions are given
in the clauses where the thermal tests are described. Except the test described under
6.3.1.1.2, only the thermal performance of the storage device itself (excluding
connecting pipes) is determined. Hence, for these tests the connections at the storage
device, as delivered by the manufacturer, are considered as the thermal demarcation
between the storage device and the testing stand.
Except the test described under 6.3.1.1.2, the solenoid valves shall be placed as near
as possible to the inlet and outlet connections of the storage device.
Connections of the store which do not lead to the charge or discharge circuit of the
testing stand shall be closed, and not connected heat exchangers shall be filled up
with water. All closed connections shall be insulated in the same way as the store.
Since fluid in closed heat exchangers expands with increasing temperature, a
pressure relief valve shall be mounted.
6.2.3 Testing of the storage device in respect of the design of the connections
The aim of the test described under 6.3.1.1.2, is to determine the influence of poor
designed store connections on the heat loss of the store (e.g. due natural convection
within one single pipe). For this test, the pipes connected to the store shall be taken
into consideration, and convection flows may not be stopped near to the storage
device by solenoid valves. Hence, for the test according to 6.3.1.1.2, the store shall be
mounted in the following manner:

Page 19
Each charge and discharge connection shall be carried out with pipes as shown in
Figure 3.
If not specified in the manufacturer’s instruction, the nominal diameter of the piping
between the store and the valves shall be equal to the nominal pipe diameter of the
store connections. The insulation shall be according to the reference conditions as
specified in annex B of EN 12976-2:2000 and annex A of ENV 12977-2:2001.
a  100 mm
b  1,5 *a
Key
1 Connecting of the connections for direct charge/discharge
2 Connecting of the heat exchangers
Figure 3 - Charge and discharge pipe connections

Page 20
6.3 Test and evaluation procedures
The aim of store testing as specified in this Prestandard, is the determination of
parameters required for the detailed description of the thermal behaviour of a hot
water store. Therefore, a mathematical computer model for the store is necessary.
The basic requirements on suitable models are specified in annex A and annex B.
The following parameters shall be known for the simulation of a store being part of a
solar system:
a) Stored water:
- Height
- Effective volume respectively effective thermal capacity
- Heights of the inlet and outlet connections
- Heat loss capacity rate of the entire store
- If the insulation varies for different heights of the store, the distribution of
the heat loss capacity rate should be determined for the different parts of
the store.
- A parameter describing the degradation of thermal stratification during
stand-by
NOTE 1 One possible way to describe this effect in a store model is the use of a
vertical thermal conduction. In this case the corresponding parameter is an effective vertical
thermal conductivity.
- A parameter describing the characteristic of thermal stratification during
direct discharge
NOTE 2 An additional parameter may be used to describe the influence of different
draw-off flow rates on the thermal stratification inside the store, if this effect is relevant.
- Positions of the temperature sensors (e. g. the sensors of the collector
loop and auxiliary heater control)
b) Heat exchangers:
- Heights of the inlet and outlet connections
- Volume
- Heat transfer capacity rate as a function of temperature
- Information on the capacity in respect of stratified charging
NOTE 3 The capacity in respect of stratified charging can be determined from the
design of the heat exchanger as well as from the course in time of the heat exchanger inlet
and outlet temperatures.
- Heat loss rate from the heat exchanger to the ambient (necessary only for
mantled heat exchangers and external heat exchangers)

Page 21
c) Electrical auxiliary heat source:
- Position in the store
- Axis direction of heating element (horizontal or vertical). If the auxiliary
heater is installed in a vertical way, also its length is required
- effectivity that characterises the fraction of the thermal converted electric
power which is actually transferred inside the store.
NOTE 4 Badly designed electrical auxiliary heaters may cause significant heat losses
during operation. In this case the electrical power supplied to the heater is not equal to the
thermal energy input to the store.
The following clauses describe the way, how the listed parameters can be determined.
Therefore, specific test sequences are necessary. The test sequences indicated by
letters (e. g. TEST A) can be subdivided into phases indicated by a number (e. g. A1 -
conditioning). Between the end of one phase and the start of the following phase, a
maximum stand-by time of 10 minutes is allowed. During this stand-by time the
ambient temperature only shall be measured and recorded.
NOTE 5 One essential point of the described methods is, that measurements inside the store
are avoided.
NOTE 6 The determination of all above listed store parameters is possible only according to
the method described under 6.3.2. However, some of the parameters may also be determined according
to the method described under 6.3.1.

Page 22
6.3.1 Determination of thermal capacity, heat loss capacity rate of the entire
store and the heat transfer capacity rate of immersed heat exchangers by means
of analytical energy and power balances
6.3.1.1 General
This clause describes the determination of the store thermal capacity and the store
heat loss capacity rate by the classical methods of the European Solar Storage
Testing Group (SSTG) (see /2/ in Bibliography).
NOTE The method for the determination of the heat transfer capacity rate of immersed heat
exchangers is adopted from /4/ (see Bibliography).
The thermal test sequences shall be carried out for the different groups of stores (see
Table 1).
6.3.1.1.1 Determination of the thermal capacity and operating heat loss capacity
rate of the entire store without pipe connections (TEST A)
This test shall be carried out for all groups of storage devices.
The storage device shall be connected to the testing stand according to 6.2.
The connections which enable a complete discharge of the store shall be fitted to the
discharge circuit of the testing stand.
The connections that enable a complete charge of the store shall be fitted to the
charge circuit of the testing stand.
For stores according to group 2 and group 4 the lowest heat exchanger will usually be
used for charging. If there exists a dead volume beneath this heat exchanger,
problems will occur when steady-state is reached. In that case, the heat loss capacity
rate cannot be determined by Test A.
- Test phase A1: conditioning until steady-state is reached
- Test phase A2: charge until steady-state is reached + 12 hours
- Test phase A3: discharge until steady-state is reached
Table 3 - Flow rates and store inlet temperatures for Test A
Test charge  circuit discharge  circuit
~ ~
~ ~ ~ ~
phase process



V V





C C,i C,o D,i D,o
D
o o o o
l/h C C l/h C C


A1 conditionin 0 - - 0,5 20,00 variable
 V
n


0,25 V
A2 charge 60,00 variable 0 - -
n


A3 discharge 0 - - 0,5 20,00 variable
V
n
Page 23
6.3.1.1.2 Determination of stand-by heat loss capacity rate of the entire store
with pipes (TEST AP)
This test shall be carried out for all groups of storage devices.
The goal of this test is to determine the heat loss capacity rate during stand-by.
However, the influence of poorly designed connections on the heat loss capacity rate
can also be determined if the heat loss capacity rates determined according to Test A
and Test AP are compared.
The storage device shall be connected to the testing stand according to 6.2.1 and
6.2.3.
The connections that enable a complete discharge of the store, shall be connected to
the discharge circuit of the testing stand.
The joins which enable a complete charge of the store shall be connected to the
charge circuit of the testing stand.
For stores according to group 2 and group 4, the lowest heat exchanger will usually be
used for charging. If there exists a dead volume beneath this heat exchanger,
problems will occur when steady-state is reached. In that case, the heat loss capacity
rate cannot be determined by Test AP.
- Test phase AP1: conditioning until steady state-is reached
- Test phase AP2: charge until steady-state is reached + 12 hours
- Test phase AP3: 48 h stand-by
- Test phase AP4: discharge until steady-state is reached
Table 4 - Flow rates and store inlet temperatures for Test AP
Test charge  circuit discharge  circuit
~ ~ ~ ~ ~ ~
phase process



V

V


C D
C,i C,o D,i D,o
o o o o
l/h C C l/h C C


AP1 conditionin 0 - - 0,5 V 20,00 variable
n


0,25 V
AP2 charge 60,00 variable 0 - -
n
AP3 stand-by 0 - - 0 - -


AP4 discharge 0 - - 0,5 V 20,00 variable
n
Page 24
6.3.1.1.3 Determination of heat transfer capacity rate of immersed heat
exchangers (TEST H).
The test procedure is based on a transient 2-sensor method using sensors
and
C,i

. An abrupt and erratic temperature change is applied to the heat exchanger under
C,o
test. The measurement of the store temperature is based on the temperature of the
heat exchanger before the abrubt change of the fluid temperature. The heat transfer
capacity rate of the heat exchanger is determined just after the end of the transient
phase.
The storage device shall be connected to the testing stand according to 6.2.
The connections which enable a complete discharge of the store, shall be connected
to the discharge circuit of the testing stand. In order to reach a complete mixture and
uniform store temperatures, the connection shall be carried out in such a way that hot
water is drawn from the top of the store and supplied to its bottom.
The connections of the heat exchanger the heat transfer capacity rate of which shall
be determined shall be connected to the charge circuit of the testing stand. The fluid
shall flow through the heat exchanger as specified by the manufacturer.
The heat transfer fluid during the test shall be that specified by the manufacturer of
the solar heating system. If no heat transfer fluid is specified by the manufacturer,
water shall be used.
The following test conditions apply:
The flow rate in the heat exchanger shall be as specified by the manufacturer. If no



flow rate is specified by the manufacturer, V = 1,2V shall be applied.
C n
The heat transfer power applied to the heat exchanger during the test shall first be
identical with the nominal one specified by the manufacturer  10 %. Additional
measurements shall be performed with half this power. If no heat transfer power is
specified by the manufacturer, P and 0,5 P shall be used.
n n
The temperature of the storage device close by the heat exchanger shall be uniform
o o o o o o
and successively adjusted to 60 C, 50 C, 40 C, 30 C, 20 C, 10 C with an
o
uncertainty not greater than 1 C.
a) Test phase H1: Initial conditioning
o
Heat up the whole storage device to 60 C by means of the charge circuit, the
discharge loop being operated as a mixing device as described above.
The heating up of the store may effected by any heating power. However, at the
end of the conditioning the heating power shall be adjusted to the nominal
heating power and the corresponding temperature at the outlet of the charge
circuit, shall be noted for further reference (see below). For the


C,o,1
monitoring of the conditioning,
. shall be applied as temperature of the
D,o
store.
Page 25
In the final stage of conditioning, the heating/cooling unit of the discharge circuit
o
may also be used to adjust more precisely the store temperature to 60 C.
b) Test phase H2: Measurement of the heat transfer capacity rate at
nominal heating power
Close SV102, open SV101 and V114, turn on P102 (see Figure 1 and 2)
Switch off the discharge circuit pump (P201) to stop mixing operation.
Wait for steady-state conditions in the store, defined (only for this purpose) as
< 0,05 K and constant for the last 5 min with an uncertainty not




, ,
C i C o C,i
exceeding 0,1 K.
Operate the charge circuit in the bypass mode at the under test phase H1
specified temperature
; wait for steady state conditions in the charge
C,o,1
circuit.
Perform the temperature change by steps in the heat exchanger as follows:
- assure that
and
are recorded with the time resolution of at least 1 s
C,i C,o
during the transient.
- Switch off P102 and close V114. Then quickly close SV101 and
simultaneously open SV102.
- After the end of the transient, the measured data may be recorded slower
again (see also 6.3.1.2.5 for more details).
NOTE 1 A typical duration of the transient is approximately 3 min.
To get a second independent measurement result, perform a second
temperature step under the same conditions.
c) Test phase H3: Measurement of the heat transfer capacity rate at
halved nominal heating power
Repeat the complete test phase H2 (two independent measurements) with a
reduced temperature of the charge circuit (instead of
) in order to operate
C,o,1
the heat exchanger at half nominal power.
d) Test phase H4: Conditioning at the next store temperature
Discharge the storage device in order to reduce its temperature by 10 K. Mix the
store thoroughly by means of the discharge circuit.

Page 26
e) Test phase H5: Measurement of the heat transfer capacity rate at
the new store temperature
Repeat test phases H2 and H3 (four independent measurements, two at
nominal and two at half nominal power).
NOTE 2 The temperature of the charge circuit which is necessary for the transmission
of the required power is determined by trial and error based on the values used at the previous
measurement steps. The overtemperature needed in the charge circuit is increasing when the
store temperature decreases, as the increasing water viscosity leads to a decrease of the heat
transfer capacity rates.
f) Test phase H6 . H9: Completion of the entire measurement sequence
o
Repeat test phases H4 and H5 down to a store temperature up to 10 C.
6.3.1.2 Evaluation of the test sequences according to 6.3.1.1 by means of
analytical energy and power balances
This clause describes the evaluation of test A according to 6.3.1.1.1,
test AP according to 6.3.1.1.2 and test H according to 6.3.1.1.3.
NOTE For the equations given for test evaluation and error analysis (equation (1) to (28)) see
also
2 in Bibliography.
The test evaluation described in this clause determines three store parameters
(thermal capacity of the entire store, operating heat loss capacity rate and stand-by
heat loss capacity rate). To obtain these parameters, the time required to reach a
steady state after an abrupt change of the inlet temperature and the store temperature
shall be calculated using the measured data.
6.3.1.2.1 Calculation of the time required for a heat store to reach steady state
after a abrupt change of the inlet temperature
For the estimation of the minimum time t required for a heat store to achieve
st, min
steady state, the following four different limit cases are considered: a store with or
without heat exchanger and with mixed or stratified characteristic during charge or
discharge.
For a stratified store without heat exchanger, t is calculated by means of
st, min
equation (1).
t  1,5 t (1)
st,min fill
Where t is the time re
...