oSIST prEN 12977-3:2006

Thermal solar systems and components - Custom built systems - Part 3: Performance characterisation of stores for solar heating systems

This standard 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.

Toplotni sončni sistemi in sestavni deli - Neserijsko izdelani sistemi - 3. del: Določanje preskusnih metod za hranilnike toplote, ogrevane s soncem

General Information

• Status: Not Published
• ICS: 27.160 - Solar energy engineering
• ICS: 91.140.10 - Central heating systems
• ICS: 91.140.65 - Water heating equipment
• Technical Committee: TOP - Thermal insulation
• Current Stage: 98 - Abandoned project (Adopted Project)
• Start Date: 19-Jan-2017
• Due Date: 24-Jan-2017
• Completion Date: 19-Jan-2017
• Mandate: M/077 - Mandate to CEN/CENELEC on standards for thermal solar systems and components
• Ref Project: prEN 12977-3 - Thermal solar systems and components - Custom built systems - Part 3: Performance characterisation of stores for solar heating systems

Overview

prEN 12977-3 - published by CEN - defines performance test methods for stores (water tanks) used in small custom-built thermal solar systems. It specifies how to characterise thermal behaviour (e.g., stratification, heat losses, heat transfer) of stores with a nominal volume between 50 and 3 000 litres and without integrated oil or gas burners. Although aimed at solar hot water systems, the test methods are applicable to any thermal store using water as storage medium (for example heat-pump buffer tanks).

Key topics and requirements

• Scope and applicability: Test methods tailored for stores used in small custom-built systems per prEN/TS 12977-1; excludes combistores (covered by prEN/TS 12977-4).
• Store classification: Definitions and categories to support consistent testing and reporting.
• Laboratory store testing: Requirements for test stands, instrumentation and measured quantities, installation and connection of stores, and controlled test procedures.
• Test and evaluation procedures: Defined test sequences, data processing methods and calculation of measured energies and powers.
• Thermal characteristics covered: Heat loss capacity rate (UA), thermal stratification behavior, effective and dead volumes, heat transfer capacity rates, and measured store heat capacity.
• Numerical model requirements: Annex A (normative) sets requirements for store simulation models; Annex B/C provide benchmark tests and parameter identification guidance.
• Verification and scaling: Annex D (informative) gives verification procedures and test sequences; Annex E discusses up/down-scaling of store parameters; Annex F addresses hot water comfort assessment.
• Test reporting: Mandatory content for test reports including store description, test results and simulation parameters.

Practical applications and users

This standard is practical for:

• Manufacturers of thermal stores and solar hot water components - to characterise product performance and support datasheets.
• Independent testing laboratories - to run repeatable, comparable store tests and provide validated parameters for simulations.
• System designers and consultants - to obtain reliable store parameters for system simulation and optimisation.
• R&D teams - to evaluate stratification, heat loss and exchanger performance under controlled conditions.
• Certification bodies and regulators - to harmonise performance claims and compliance testing.

Using prEN 12977-3 helps ensure consistent, comparable performance data for thermal stores used in solar heating systems, improving accuracy of system simulations and enabling better system sizing and product selection.

Related standards

• prEN/TS 12977-1, -2, -4 (custom-built system parts)
• EN 12976-2 (factory-made systems)
• ISO 9459-5 (whole system tests and simulation)
• EN ISO 9488 (solar energy vocabulary)

Standards Content (Sample)

SLOVENSKI STANDARD
01-november-2006
7RSORWQLVRQþQLVLVWHPLLQVHVWDYQLGHOL1HVHULMVNRL]GHODQLVLVWHPLGHO
'RORþDQMHSUHVNXVQLKPHWRG]DKUDQLOQLNHWRSORWHRJUHYDQHVVRQFHP
Thermal solar systems and components - Custom built systems - Part 3: Performance
characterisation of stores for solar heating systems
Ta slovenski standard je istoveten z: prEN 12977-3
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 STANDARD
DRAFT
NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2006
ICS 91.140.10; 91.140.65; 27.160 Will supersede ENV 12977-3:2001
English Version
Thermal solar systems and components - Custom built systems
- Part 3: Performance test methods for solar water heater stores
Installations solaires thermiques et leurs composants - Thermische Solaranlagen und ihre Bauteile -
Installations assemblées à façon - Partie 3: Méthodes Kundenspezifisch gefertigte Anlagen - Teil 3:
d'essai des performances des dispositifs de stockage des Leistungsprüfung von Warmwasserspeichern für
installations de chauffage solaire de l'eau Solaranlagen
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee CEN/TC 312.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations which
stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other language
made by translation under the responsibility of a CEN member into its own language and notified to the Management Centre has the same
status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to
provide supporting documentation.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and
shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2006 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 12977-3:2006: E
worldwide for CEN national Members.

Contents Page
Foreword.4
Introduction .4
1 Scope.4
2 Normative references.4
3 Terms and definitions .5
4 Symbols and abbreviations .9
5 Store classification.10
6 Laboratory store testing.10
6.1 Requirements on the testing stand.10
6.1.1 General.10
6.1.2 Measured quantities and measuring procedure.14
6.2 Installation of the store .15
6.2.1 Mounting.15
6.2.2 Connection.15
6.3 Test and evaluation procedures.15
6.3.1 Test sequences.17
6.3.2 Data processing of the test sequences.28
7 Store test combined with a system test according to ISO 9459-5.29
8 Test report.29
8.1 General.29
8.2 Description of the store .30
8.3 Test results.31
8.4 Parameters for the simulation.31
Annex A (normative) Requirements for the numerical store model .33
A.1 General.33
A.2 Assumptions.33
A.3 Energy balance.33
Annex B (normative) Store model benchmark tests .35
B.1 General.35
B.2 Temperature of the store during stand-by .35
B.3 Heat transfer from heat exchanger to store.35
Annex C (normative) Benchmarks for the parameter identification .37
Annex D (informative) Verification of store test results.38
D.1 General.38
D.2 Test sequences for verification of store test results .38
D.2.1 Verification sequences from measurements on a store testing stand .38
D.2.2 Test sequences obtained during a whole system test according ISO 9459-5 .45
D.3 Verification procedure.45
D.3.1 General.45
D.3.2 Error in transferred energies .45
D.3.3 Error in transferred power .46
Annex E (informative) Determination of store parameters by means of “up-scaling” and “down-
scaling”.47
E.1 General.47
E.2 Requirements.47
E.3 Determination of store parameters.48
E.3.1 Thermal capacity of store.48
E.3.2 Height of store .48
E.3.3 Determination of heat loss capacity rate .48
E.3.4 Relative heights of the connections and the temperature sensors .48
E.3.5 Heat exchangers.48
E.3.6 Parameter describing the degradation of thermal stratification during stand-by.49
E.3.7 Parameter describing the quality of thermal stratification during direct discharge .49
Annex F (informative) Determination of hot water comfort.50
F.1 General.50
Bibliography.51

Foreword
This document (prEN 12977-3:2006) has been prepared by Technical Committee CEN/TC 312 “Thermal solar
systems and components”, the secretariat of which is held by ELOT.
This document is currently submitted to the CEN Enquiry.
This document will supersede ENV 12977-3:2001.
The annexes A, B, C are normative and annexes D and E are informative.
Introduction
The test methods for stores of solar heating systems as described in this document are required for the
determination of the thermal performance of small custom built systems as specified in prEN/TS 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 thermal solar system.
NOTE 1 The already existing test methods for stores of solar heating systems are not sufficient with regard to thermal
solar systems. 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 document for the
performance characterisation of stores for solar heating systems is needed.
NOTE 2 For additional information about the test methods for the performance characterisation of stores see [1] in
Bibliography.
1 Scope
This document (prEN 12977-3:2006) specifies test methods for the performance characterization of stores
which are intended for use in small custom built systems as specified in prEN/TS 12977-1.
Stores tested according to this document are commonly used in solar hot water systems. However, also the
thermal performance of all other thermal stores with water as storage medium can be assessed according to
the test methods specified in this document.
The document applies to stores with a nominal volume between 50 l and 3 000 l.
This document does not apply to combistores. Performance test methods for solar combistores are specified
in prEN/TS 12977-4.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
EN 806-1, Specifications for installations inside buildings conveying water for human consumption — Part 1:
General
EN 1717, Protection against pollution of potable water installations and general requirements of devices to
prevent pollution by backflow
EN 12828, Heating systems in buildings — Design of water-based heating systems
EN 12976-2, Thermal solar systems and components — Factory made systems — Test methods
prEN/TS 12977-1, Thermal solar systems and components — Custom built systems — Part 1: General
requirements for solar water heaters and combi systems
prEN/TS 12977-2, Thermal solar systems and components — Custom built systems — Part 2: Test methods
for solar water heaters and combi systems
prEN/TS 12977-4, Thermal solar systems and components — Custom built systems — Part 4: Performance
test methods for solar combistores
EN ISO 9488, Solar energy — Vocabulary
ISO/DIS 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 document, the terms and definitions given in EN ISO 9488 and the following 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
3.3
charge connection
pipe connection used for charging the storage device
3.4
combistore
one store used for both domestic hot water preparation and space heating
3.5
~
constant inlet temperature, ϑ
x,i
~
temperature which is achieved during charge (x = C) or discharge (x = D), if the mean value ϑ over the
x,i
~
period of 0,5 “reduced charge / discharge volume” (see 3.34) is within (ϑ ± 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 charge volumes is
c
~
within ( P ± 10) %
c
3.8
conditioning
~
process of creating a uniform temperature inside the store by discharging the store with ϑ = 20 °C until a
D,i
steady state is reached
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
volume / capacity of the store which is only heated due to heat conduction (e. g. below a heat exchanger)
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
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
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 mentioned without specification, (UA)
s,a s,a
represents the stand-by heat loss capacity rate.
3.18
heat transfer capacity rate
thermal power transferred per K temperature difference
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
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
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 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
xp
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
xp
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
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
sum over all thermal capacities m × c of the entire store (fluid, tank material, heat exchangers) having part of
i p,i
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
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) circuit, in W
x,m
P predicted power transferred through the charge (x = C) or discharge (x = D) circuit, in W
x,p
Q measured energy transferred through the charge (x = C) or discharge (x = D) circuit, in J
x,m
Q predicted energy transferred through the charge (x = C) or discharge (x = D) circuit, in J
x,p
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
ϑ ambient temperature, in °C
a
ϑ store temperature, in °C
s
~
ϑ inlet temperature of the charge (x = C) or discharge (x = D) circuit, in °C
x,i
ϑ constant inlet temperature of the charge (x = C) or discharge (x = D) circuit, in °C
x,i
ϑ 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
∆ϑ mean logarithmic temperature difference, in K
m
ε relative error in mean power transferred during charge (x = C) or discharge (x = D), in %
x,P
ε relative error in energy transferred during charge (x = C) or discharge (x = D), in %
x,Q
ρ density, in kg/m³
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.
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.
The testing stand shall be located in an air-conditioned room where the room 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 m³/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).
Key
FF Flow meter SV Solenoid valve
HX Heat exchanger TT Temperature sensor
OP Overheating protection TIC Temperature indicator and controller
P Pump V Valve
ST Store
Figure 1 — Charge circuit of the store testing stand
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.

Key
FF Flow meter TT Temperature sensor
HX Heat exchanger TIC Temperature indicator and controller
P Pump V Valve
SV Solenoid valve
Figure 2 — Discharge circuit of the store testing stand
6.1.2 Measured quantities and measuring procedure
The quantities listed in Table 2 shall be measured with the given accuracy:
Table 2 — Measuring data
Measuring device
Measured quantities (see Figure 1 and Uncertainty
2)
&
FF105 2,0 %
Volume flow, V , in the charge circuit between 0,05 m³/h and 1 m³3/h
C
& FF205 2,0 %
Volume flow, V , in the discharge circuit between 0,05 m³/h and 1 m³/h
D
TT101 0,1 K
Temperature, ϑ , of the charging medium at store inlet
C,i
TT102 0,1 K
Temperature, ϑ , of the charging medium at store outlet
C,o
Difference in the charging medium temperature, ∆ϑ , between store TT101 and TT102 0,02 K
C
inlet and store outlet: (for tests according to 6.3.1)
Difference in the charging medium temperature, ∆ϑ , between store TT101 and TT102 0,05 K
C
inlet and store outlet: (for tests according to 6.3.2)
Temperature, ϑ , of the discharging medium at store inlet TT201 0,1 K
D,i
TT202 0,1 K
Temperature, ϑ , of the discharging medium at store outlet
D,o
Difference in the discharging medium temperature, ∆ϑ , between store TT201 and TT202 0,02 K
D
inlet and store outlet: (for tests according to 6.3.1)
Difference in the discharging medium temperature, ∆ϑ , between store TT201 and TT202 0,05 K
D
inlet and store outlet: (for tests according to 6.3.2)
Ambient temperature ϑ TT001 0,1 K
am
& – 2 %
Electric power, Q , (auxiliary heating)
el
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 during the transient the temperatures shall be
measured and recorded every second.
The temperature sensors shall have a relaxation time of less than 10 s (i. e. 90 % of the temperature variation
is detected by the sensor immersed in the heat transfer fluid within 10 s 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 m³/h, temperatures 20 °C, 40 °C, 60 °C, 80 °C). If the measured temperature difference exceeds the
permissible uncertainty of 0,0 K / 0,05 K, the temperature sensors shall be calibrated.
A reference heater may also be used for the zero measurement.
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 EN 12828.
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.
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.
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.
NOTE The performance of a solar heating system depends on the individual installation and actual boundary
conditions. With regard to the heat losses of the store besides deficits in the thermal insulation, badly designed
connections can increase the heat loss capacity rate of the store due to natural convection that occurs internally in the
pipe. In order to avoid this effect the connections of the pipes should be designed in such a way that no natural convection
inside the pipe occurs. This can e. g. be achieved if the pipe is directly going downwards after leaving the store or by using
a siphon.
6.3 Test and evaluation procedures
The aim of store testing as specified in this document, 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).
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 min 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.
6.3.1 Test sequences
This clause describes the thermal test sequences for the different groups of stores.
6.3.1.1 General
In the following, the conditions are specified under which the stores shall be tested. An overview on the test
sequences for determination of the different store parameters is given in Table 3.
Table 3 — Compilation of the test sequences
Purpose of test Test Clause
Determination of the store volume, the heat transfer Test C:
capacity rate of the lowest heat exchanger and the
group 1 6.3.1.2.1
thermal stratification during discharge.
group 2 6.3.1.2.2
group 3 6.3.1.2.3
group 4 6.3.1.2.4
Determination of the thermal stratification during Test S 6.3.1.3
discharge with a 'high' flow rate
Determination of the heat loss capacity rate of the Test L:
entire store during stand-by
group 1 6.3.1.4.1
group 2 6.3.1.4.2
group 3 6.3.1.4.3
group 4 6.3.1.4.4
Determination of the heat transfer capacity rate and Test NiA for stores with auxiliary 6.3.1.5
the position of the auxiliary heat exchanger(s) heat exchanger(s)
Determination of the position and length of the Test EiA for stores with electrical 6.3.1.6
electrical heating element(s) heating elements
Determination of the degradation of thermal Test NiA and Test NiB for stores of 6.3.1.7.1
stratification during stand-by group 1 and 3 6.3.1.7.1
Test NiA and Test NiB for stores of 6.3.1.5
group 2 and 4 6.3.1.7.2
Test EiA and Test EiB for stores 6.3.1.6
with electrical auxiliary heating 6.3.1.7.3
elements only
NOTE 1 The exact vertical positions of the temperature sensors as well as the upper connections of the heat
exchangers above which the store is charged mixedly, have a minor influence on the thermal behaviour of the store.
Hence these vertical positions need not to be determined by means of parameter identification. It is recommended to
measure the corresponding positions or to determine them from the drawing of the store.
The following applies to all tests for determination of the heat transfer capacity rate of the heat exchangers:
The flow rates through the heat exchangers as well as the heating powers which are given for the
determination of the heat transfer capacity rate (dependent on temperature) of the heat exchangers are
recommendations. Other flow rates and heating powers may also be used, if they better correspond to the real
operating conditions or are specified in the manufacturers instruction. This shall, however, be specified in the
test report.
NOTE 2 The heat transfer capacity rate of immersed heat exchangers is increasing with the mean local temperature
(the water becomes more dilute), the transmitted heating power and the flow rate through the heat exchanger. Therefore,
different results for different operating conditions are expected.
6.3.1.2 Determination of the store volume, the heat transfer capacity rate of the lowest heat exchanger and
the thermal stratification during discharge (Test C)
The store volume determined by the method described below is the effective store volume.
NOTE For stores with a dead volume, the effective thermal capacity determined according to 6.3.1.1 is greater than
the store volume, or the thermal capacity of the entire store, determined according to this clause. This effect is to be
explained by the long charging period which is necessary to achieve steady-state conditions and during which the fluid in
the dead volume is heated due to heat conduction. During usual operation, no heat is stored in the dead volume. Hence,
for stores with a dead volume, the effective store volume is less than the store volume measured in litres. The effective
store volume may be determined by a test sequence by means of which it is not intended to reach steady-state conditios.
The heat transfer capacity rate of the heat exchangers refers to heat exchangers which are not separated
from the storage device.
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 which enable a complete charge of the store, shall be fitted to the charge circuit of the testing
stand.
6.3.1.2.1 Group 1
The goal of this test is the determination of the effective store volume and the thermal stratification during
discharge with a relatively 'low' flow rate.
Test C (group 1)
 Test phase C1: conditioning until steady-state is reached,
 test phase C2: charging until ϑ = 55 °C,
C,
 test phase C3: discharging until steady-state is reached.
Table 4 — Flow rates and store inlet temperatures for Test C (group 1)
Charge circuit Discharge circuit
Test ~ ~ ~ ~ ~ ~
Process & &
ϑ ϑ ϑ ϑ
V V
C,i C,o D,i D,o
C D
phase
°C °C °C °C
l/h l/h
C1 conditioning 0 – – & 20,00 variable
0,5 × V
n
C2 charge & 60,00 variable 0 – –
0,5 × V
n
&
C3 discharge 0 – – 20,00 variable
0,5 × V
n
6.3.1.2.2 Group
...