PUBLIC REVIEW DRAFT, SEPTEMBER 2008KENYA STANDARD  KS 1855-3:2008  
ICS 27.160; 97.100.99 
  
 
 
  
 
  
 
  
 
Thermal solar systems and components — 
Custom built systems — Part 3: Performance 
characterization of st ores for solar heating 
Systems 
 
 
  
 
  
 
 
  
Public Review Draft, September 2008  
 
 
  
 
  
 
  
 
  
 
© KEBS 2008 Edition 1.0 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
ii © KEBS 2008 — All rights reserved  
TECHNICAL COMMITTEE REPRESENTATION 
 
The following organizations were represented on the Technical Committee 
 
Kenital Solar (K) Ltd  
ASP Solar (Kenya) Ltd  
Sollatek Ltd  
Department of Electrical & Electronic Engineering, JKUAT  
Renewable Energy Department, Ministry of Energy  
Chloride Exide Kenya Limited  
Energy Alternatives Africa Ltd  
Solarnet  
Automotive and Industrial Battery Manufacturers (AIBM) (K) Ltd 
RENCON Associates  
Telesales Solar Ltd 
Kenya Industrial Research and Development Institute, KIRDI 
Kenya Bureau of Standards — Secretariat 
 
 
 
 
  
 
 
 
 
  
REVISION OF KENYA STANDARDS 
 
In order to keep abreast of progress in industry, Kenya standards shall be regularly reviewed. Suggestions for 
improvement to published standards, addressed to the Managing Director, Kenya Bureau of Standards, are 
welcome. 
 
© Kenya Bureau of Standards, 2008 
 
Copyright. Users are reminded that by virtue of Section 25 of th e Copyright Act, Cap. 12 of 2001  of the Laws of Kenya, copyrig ht 
subsists in all Kenya Standards and except as provided under Section 26 of this Act, no Kenya Standard produced by Kenya Bureau  of 
Standards may be reproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in w riting 
from the Managing Director. 
. 
 
 
 
 
 
   
 
 
 
 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
ICS 27.160; 97.100.99  
© KEBS 2008 — All rights reserved iii  
 
 
 
 
 
 
 
 
  
 
 
Thermal solar systems and components — 
Custom built systems — Part 3: Performance 
characterization of stores for solar heating 
Systems 
 
 
 
 
 
 
 
  
 
  
KENYA BUREAU OF ST ANDARDS (KEBS) 
 
Head  Office:  P.O. Box 54974, Nairobi-00200, Tel.: (+254  020) 605490, 602350, Fax: (+254 020)  604031 
E-Mail: info@kebs.org,  Web:http://www.kebs.org   
 
KEBS Coast Region 
P.O. Box 99376, Mombasa 80100 
Tel: (+254 041) 229563, 230939/40 Fax: (+254 041) 229448 
E-mail: kebs-msa@swiftmombasa.com
 KEBS Lake Region 
P.O. Box 2949, Kisumu 40100 
Tel: (+254 057) 23549,22396 Fax: (+254 057) 21814 E-mail: kebs-ksm@swiftkisumu.com
 KEBS North Rift Region 
P.O. Box 2138, Nakuru 20100 
Tel: (+254 051) 210553, 210555
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
iv © KEBS 2008 — All rights reserved  
Foreword 
 
This Kenya standard was developed by the Renewable Energy Resources Technical Committee under the supervision of the Electrical Industry Standards Committee and is in accordance with the procedures of the 
Bureau. 
 
The test methods for stores of solar heating systems as described in this Kenya Standard are required for the 
determination of the thermal performance of small custom built systems as specified in KS 1855-1.  
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.  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008  
© KEBS 2008 — All rights reserved v  
Contents 
 
1 Scope ......................................................................................................................... ................................ 1  
2 Normative references .......................................................................................................... ....................... 1  
3 Terms and definitions ......................................................................................................... ........................ 1  
4 Symbols and abbreviations ..................................................................................................... ................... 5  
5 Store classification .......................................................................................................... ........................... 6  
6 Laboratory store testing ...................................................................................................... ........................ 6  
7 Store test combined with a system test according to IS O 9459-5 ........................................................... 37  
8 Test report ................................................................................................................... ............................. 38  
Annex A (normative)  Requirements for the numerical store model ............................................................... .. 40 
Annex B (normative)  Store model benc hmark tests .............................................................................. .......... 42  
Annex C (normative)  Benchmarks for the parameter identification .............................................................. ... 44 
Bibliography .................................................................................................................. .................................... 46  
 
 
 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008PUBLIC REVIEW DRAFT, SEPTEMBER 2008KENYA STANDARD KS 1855-3:2008  
© KEBS 2008 — All rights reserved 1  
 
Thermal solar systems and components  — Custom built systems — Part 
3: Performance characte rization of stores for solar heating systems  
 
1 Scope 
 
This Kenya Standard specifies test methods for the performance characterization of stores which are intended for use in small custom built systems as specified in KS 1855-1. 
 
Stores tested according to this Kenya Standard 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 Kenya Standard.  
The Standard applies to stores with a nominal volume between 50 and 3000 litres and without integrated oil 
or gas burner.  
2 Normative references 
 
The following referenced documents are indispensable for the application of this Kenya Standard. For dated 
references, only the edition cited applies. For undated re ferences, the latest edition of the referenced document 
(including any amendments) applies.  
 
KS 1852-2, Thermal solar systems and components ― Factory made systems ― Test methods  
 
KS 1855-2, Thermal solar systems and components ― Custom built systems ― Test methods  
 ISO 9774, Thermal insulation for building applications  — Guidelines for selecting properties  
 
ISO 16528, Boilers and pressure vessels  
 
ISO 9488, Solar energy ― Vocabulary  
 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 Kenya Standard the following terms and definitions together with 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 
 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 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
2 © KEBS 2008 — All rights reserved  
3.5 
constant inlet temperature (ix,~ϑ) 
temperature which is achieved during charge (x = C) or discharge (x = D), if the mean value ix,~ϑover the 
period of 0.5 reduced charge / discharge volumes (see 3.34) is within ix,~ϑ± 1) °C 
 
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 (c~P) 
charge power which is achieved, when the mean value c~P over the period of 0.5 reduced charge volumes is 
within c~P + 10 % 
 
3.8 
conditioning 
process of creating a uniform temperature inside the store by discharging the store withiD,ϑ = 20 °C until a 
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., a u niform 
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) 
 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 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 3  
3.16 
external auxiliary heating 
considered as part of the store under test 3.17 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 
 
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)s,a is to mentioned without specification, ( UA)s,a represents the stand-by heat loss 
capacity rate. 
 
3.18 
heat transfer capacity rate 
the 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 
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 ( Px,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 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
4 © KEBS 2008 — All rights reserved 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 (nv&) 
the nominal volume of the entire store divided by 1 h 
 
3.29 
nominal heating power ( Pn) 
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,sa 
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 ( Qx,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 
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 o f 
the discharge circuit may occur during the discharge of the first st ore volume before the outlet temperature drops rapidly. Thi s state is not 
considered as steady state. 
 
3.38 
store temperature 
temperature of the store medium 
 
3.39 
Stratified PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 5 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
i × Cp,i of the entire store (fluid, tank material, 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 
  
4 Symbols and abbreviations 
 
Cs thermal capacity of the entire store, in J/K 
 
CP specific heat capacity, in J/(kg K) 
 P
n nominal heating power, in W 
 
Px,m measured power transferred through the charge (x=C) or discharge (x=D) circuit, in W 
 
Px,p predicted power transferred through the charge (x=C) or discharge (x=D) circuit, in W 
 
Qx,m measured energy transferred through the charge (x=C) or discharge (x=D) circuit, in J 
 
Qx,p predicted energy transferred through the charge (x=C) or discharge (x=D)circuit, in J 
 
tst time required to achieve a steady state, in s 
 
tx,f transfer time for charging (x=C) or discharging (x=D) , in s 
 
aϑ ambient temperature, in °C 
 
sϑ store temperature, in °C 
 
ix,~ϑ inlet temperature of the charge (x=C) or discharge (x=D) circuit, in °C 
 
ix,ϑ constant inlet temperature of the charge (x=C) or discharge (x=D) circuit, in °C 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
6 © KEBS 2008 — All rights reserved ox,ϑ outlet temperature of the charge (x=C) or discharge (x=D) circuit, in °C 
 
(UA)hx,s heat transfer capacity rate between heat exchanger and store, in W/K 
 
(UA)s,a heat loss capacity rate of the store, in W/K 
 (UA)
op,s,a operating heat loss capacity rate of the store, in W/K 
 (UA)
sb,s,a stand-by heat loss capacity rate of the store, in W/K 
 
\/n nominal volume of the store, in l 
 
nV& nominal flow rate, in l/h 
 
x~v& constant flow rate of the charge (x=C) or discharge (x=D) circuit, in l/h  
 
mϑΔ mean logarithmic temperature difference, in K 
 ε
x,P relative error in mean power transferred du ring charge (x=C) or discharge (x=D), in % 
 
εx,Q relative error in energy transferred during charge (x=C) or discharge (x=D), in % 
 
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. 
 
NOTE 2 Stores that can be charged or discharged directly and indi rectly (e. g. a store of a space heating system with an intern al heat 
exchanger for the preparation of domestic hot water) can belong to more than one group. In this case the appropriate test proce dures 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. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 7  
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 t he 
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 fo r 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 ci rcuited" and operated at room temperature, ("short circuited" m eans that no 
storage device is connected and SV102, V113, V115and V116 are closed, see Figure 1). 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
8 © KEBS 2008 — All rights reserved 
 Key 
FF Flow meter 
HX Heat exchanger 
OP Overheating protection 
P Pump 
Figure 1 — Charge circuit of the store testing stand Key 
ST Store 
SV Solenoid valve 
TT Temperature sensor 
TIC Temperature indicator and controller 
V Valve 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 9  
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 stan d. 
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 occurring during the tests. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
10 © KEBS 2008 — All rights reserved 
 
Key  SV Solenoid valve 
FF Flow meter TT Temperature sensor 
HX Heat exchan ger TIC Temperature indicator and controlle r
P Pump V Valve 
 
Figure 2 — Discharge circuit of the store testing stand 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 11  
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 
(see Figure 1 and 2) Uncertainty 
volume flow VC in the charge circuit between 0.05 m3/h 
and 1 m3/h 
 FF105 
 2.0 % 
 
volume flow CV& in the discharge circuit between 0.05 
m3/h and 1 m3/h 
 FF205 
 2.0 % 
 
temperature iC,ϑ of the charging medium at store inlet 
 TT101 
 0.1 K 
 
temperature C,0ϑ of the charging medium at store outlet 
 TT102 
 0.1 K 
 
difference in the charging medium temperature 
CϑΔbetween store inlet and store outlet: (for tests 
according to 6.3.1 ) 
 TT101 andTT102 
 0.02 K 
 
difference in the charging medium temperature CϑΔ
between store inlet and store outlet: (for tests according to 6.3.2)  TT101 andTT102 
 0.05 K 
 
temperature iD,ϑ of the discharging medium at store 
inlet 
 TT201 
 0.1 K 
 
temperature, D,0ϑ of the discharging medium at store 
outlet  TT202 
 0.1 K 
 
difference in the discharging medium temperature DϑΔ
between store inlet and store outlet: (for tests according to 6.3.1)  TT201 and TT202 
 0.02 K 
 
difference in the discharging medium temperature DϑΔ
between store inlet and store outlet: (for tests according 
to 6.3.2) 
 TT201 and TT202 
 0.05 K 
 
ambient temperature amϑ 
 TT001 
 0.1 K 
 
electric power elQ& (auxiliary heating) 
 - 
 2% 
 
 
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. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
12 © KEBS 2008 — All rights reserved 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 m3/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. 
 
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 ISO 9774.  
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 nearer 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 fille d up 'with water. All clos ed 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: 
 
Each charge and discharge connection shall be carried out with pipes as shown in Figure 3. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 13 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 KS 1852-2 and annex A of KS 1855-2. 
 
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 
 
6.3 Test and evaluation procedures 
 
The aim of store testing as specified in this Kenya Standard, 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 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
14 © KEBS 2008 — All rights reserved ⎯ 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. 
 
NOTE 2 An additional parameter may be used to describe the influence of different draw-off flow rates on the thermal stratifica tion 
inside the store, if this effect is relevant. 
 
⎯ Positions of the temperature sensors (e. g. the se nsors 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 vertic al). If the auxiliary heater is installed in a vertical 
way, also its length is required 
 
⎯ effectivity that characterizes the fraction of the thermal converted electric power which is actually 
transferred inside the store. 
 
NOTE 4 Badly designed electrical auxiliary heaters may caus e significant heat losses during operation. In this case the electri cal 
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. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 15  
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 Jesting 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 
 
Test 
  
 Charge circuit 
 Discharge circuit 
 
phase 
 process 
 C~
V& 
l/h iC,~ϑ  
°C C,0~ϑ 
°C DV~& 
l/h iD,~V 
°C D,0~ϑ 
°C 
A1 
 conditioning
 0 
 — — 0.5 × nv& 
 20.00 
 variable 
 
A2 
 charge 
 0.25 × nv& 60.00 
 variable 
 0 
 — — 
A3 discharge 0 — — 0.5 × nv& 20.00 variable 
 
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. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
16 © KEBS 2008 — All rights reserved 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 APS:  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 
phase Process 
 charge circuit Discharge circuit 
C~
V& 
l/h ϑ~
c,i 
°C 0,~
cϑ 
°C D~ν& 
l/h iD,~ϑ 
°C iD,~
ϑ& 
°C 
AP1 conditioning 0 — — 0.5 xnν& 20.00 variable 
AP2 charge 0.25 × nv& 60.00 variable 0 — — 
APS stand-by 0 — — 0 — — 
AP4 discharge 0 — — 0.5 × nv& 20.00 variable 
 
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 iC,ϑ and C,0ϑ. An abrupt and 
erratic temperature change is applied to the heat exchanger under 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, 
n C .V V& &×=21  shall be applied.  
 
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, Pn and 0.5 × Pn shall be used. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 17  
The temperature of the storage device close by the heat exchanger shall be uniform and successively 
adjusted to 60 °C, 50 °C, 40 °C, 30 °C, 20 °C, 10 °C with an uncertainty not greater than 1 °C. 
 
a) Test phase H1: Initial conditioning 
 
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, 
o,1c,ϑ  shall be noted for further reference (see below). For the monitoring 
of the conditioning, .oD,ϑ shall be applied as temperature of the store. 
 
In the final stage of conditioning, the heating/cooling unit of the discharge circuit 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 
C,0 iC,ϑϑ− < 0.05 K 
andic,ϑ constant for the last 5 min with an uncertainty not exceeding 0.1 K. 
 
Operate the charge circuit in the bypass mode at the under test phase H1 specified temperature
0,1c,ϑ; 
wait for steady state conditions in the charge circuit. 
 
Perform the temperature change by steps in the heat exchanger as follows: 
 
⎯ Assure that iC,ϑ and C,0ϑare recorded with the time resolution of at least 1 s 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 
C,0,1ϑ ) in order to operate 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. 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
18 © KEBS 2008 — All rights reserved 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 measur ement steps. The overtemperature needed in the charge circuit is  
increasing when the store temperature decreases, as the increas ing water viscosity leads to a decrease of the heat transfer 
capacity rates. 
 
f) Test phase H6 …. H9: Completion of the entire measurement sequence 
 
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 A according to 6.3.1.1.1 and 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 analys is (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
st, min required for a heat store to achieve 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, tst, min is calculated by means of equation (1). 
 
tst, min = 1.5 × tfill (1) 
 
Where tfill, is the time required for the exchange of one store volume. 
 
The typical example of such a store is hot water store with direct discharge. A store of this type reaches 
steady-state conditions after 1.5 fill times at least. 
 
For a stratified store with heat exchanger, equation (2) is used. The derivation of tst, mix has been effected for 
the completely mixed store. Since quite some heatstores with heat exchanger which are praised as 
"stratified" behave, in reality, more or less mixed, th e same criterion is here applied as for the completely 
mixed store. The factor 1.5 takes into account possible errors in respect of the estimation of the heat transfer 
capacity rate between the heat exchanger and the store (UA) hx,s. 
 In the course of a test, (UA)
hx,s is not constant. Especially by approach ing steady-state conditions, its value 
generally decreases. 
 
tst,min = 1.5 × tst,mix (2) 
 where t
st mix is determined from equation (6). 
 For a completely mixed store with heat exchanger, t
st, min is also calculated from equation (2). 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 19 For a fully mixed store without heat exchanger (where there is no uncertainty with respect to ( UA)hx,s, ε = 1), 
equation (3) applies. 
 
tst,min = 1.5 × tst,mix (3) 
 After the period t
st, mix the heat flow supplied to a fully mixed store (which actually reaches steady-state 
conditions after infinite time) is less than 1.05 times the heat flow emitted from the store In that case the error 
in (UA)s,a due to insufficiently reached steady-state conditions is less than 5 % (equation (4)). 
 
() ( )a mixst, as, e i p H ) ( )(05.1 ϑ ϑ ϑϑρ − ××<−×××= ts UA c V Q&& 
= ()() ()( )a mixst,s as, mixst,s i p )(05.1 ϑ ϑ ϑϑερ − ××< −×××× t UA t c V&  (4) 
 
For tests where the store is discharged up to the ambient temperature, the right member of equation (4) can 
become very small, leading to large values for tst, mix that may exceed the time which is available for the test. 
In those cases a default value of ( UA)s,a should be used. 
 
The store temperature, )(stϑ  can for a completely mixed store with heat exchanger (( UA)hx,s = constant) be 
calculated from equation (5). 
 
)(stϑ  = k 0 + (xtK t×−×−2k
0 0s e) )(ϑ  (5) 
 
Where  k 0 = 
as, pa as, i p
)()(
UA c VUA c V
+×××× +××××
ερϑ ϑερ
&&
 
 
and  k 2 = 
ms,as, p )(
CUA c V +××× ερ&
 
 
Where  
t
0 is the time at which the step with the heat exchanger effectiveness occurs. 
 
NTUe−−=1ε  
 
tst,mix is obtained by substitution of )(stϑ  in equation (4) and conversion (equation (6)). 
 
tst,mix = ⎥
⎦⎤
⎢
⎣⎡
−−×
0 10 s,1
2ln1
kkk
kϑ (6) 
 
where k 1 = 
as, pa as, i,2 p
)(05.1)(05.1
UA c VUA c V
×+×××××+××××
ερϑ ϑερ
&&
 
 
6.3.1.2.2 Estimation of the store temperature 
 
The store temperature which is estimated for determination of Cs,m and ( UA)s,a shall be accurate especially 
under steady-state conditions. As ( UA)s,a is based on the difference between the temperatures of the store 
and the ambient, the store temperature is also needed for the calculation of the heat losses during the 
transient between two steady-state conditions. As the store temperature generally increases or decreases 
rapidly (75 % to 80 % of the step are already reached after 2 or 3 exchanges of the storage fill), a greater 
error in 5S during the transient can be accepted as it will not affect significantly the total heat loss between 
two steady-states and, consequently, C s, m. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
20 © KEBS 2008 — All rights reserved As in 6.3.1.2.1, also here a distinction has been made according to the four types of stores. 
 
For a stratified store without heat exchanger, Sϑ is estimated from equation (7) for the steady state and from 
equation (8) during the transient. 
 
2c i
sϑϑϑ+=  (7) 
 
⎥
⎦⎤
⎢
⎣⎡ +−+×++=2 2 2lc, li, 2,2 i,2
Hlc, li,
sϑϑϑϑ ϑϑϑ t  (8) 
 
with tH = 
cf0
ttt−, if t H < 0, t H = 0 and if tH >1, tH = 1. 
 
where  
 t
0 time at which step occurs 
 
The maximal possible error in Sϑ from equation (7) is 
 
2c i
sδϑδϑδϑ+=  (9) 
 
 
As stated above, the error in Sϑ during the transient can be neglected. 
 
For a stratified heat store with heat exchanger, the store temperature can be estimated from equation (10) 
and the error in sϑ from equation (11). 
 
NTUci, c i
s2ϑϑϑϑΔ−+=  (10) 
 
2, ,
2 NTUNTUx
NTUei ei c sΔ+Δ+= δδϑδδϑδϑ (11) 
 
For a completely mixed store with heat exchanger, the store temperature can be estimated from equation 
(12) and the error from equation (13).  
NTUe−−Δ−=
1ei,
i sϑϑϑ  (12) 
 
()2 ei,ei,
i s
1x
1 NTUNTU
NTUeeNTU
e −−
−−Δ×+
−Δ+= ϑ δϑδδϑδϑ  (13) 
 
To avoid physically impossible values of the store temperature (sϑ<s,1ϑ) due to underestimation of ( UA)hx,s 
and during the residence time of the heat transfer fluid in the heat exchanger, in all cases where sϑ< s,1ϑ 
calculated, sϑ = eϑ is set in the evaluation. 
 
For a fully mixed store without heat exchanger (NTU = ∞), equation (12) gives: 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 21 e sϑϑ= (14)  
and 
 
e sδϑδϑ=  (15) 
 
6.3.1.2.3 Determination of the operating heat loss capacity rate ( UA)op,s,a 
 
The operating heat loss capacity rate ( UA)op,s,a is determined under steady-state conditions from equation 
(16) over a period of tL (it is recommended to use tL = 16 h). 
 
(UA)op,s,a = dtdc V
ttt
tt×−×××
×∫+L st
sa sei, p
L1
ϑϑϑ ρ&
 (16) 
 
where 
 
tst time after which the store has reached steady state. 
 
The error of ( UA)s,a is calculated by equation (17): 
  
⎥⎥
⎦⎤
⎢⎢
⎣⎡
−+−++ΔΔ++×
a ss
a sa
ei,ei,
pρ
as,op,)(ϑϑδϑ
ϑϑδϑ
νδν
ϑϑδδ
ρδρδcc
UA   (17) 
 
Relative errors in the density and specific heat capacity of the water are neglected as well as the error in the 
measurement of the time tL. Errors in inlet temperature, temperature difference across the store and flow rate 
depend on the individual test facility. 
 
For the determination of the error in respect of the ambient temperature aϑ, not only the measurement error 
but also possible fluctuations of the ambient temperature shall be considered as these lead to uncertainties in 
(UA)op,s,a, too. It is obvious that short-time fluctuations of a few minutes do not influence the result as ( UA)op,s,a 
is calculated as a mean value over 16 hours. If there is a drift in the ambient temperature, the application of a 
mean ambient temperature leads, however, to a systematical error due to an insufficient steady-state.  
It is neither possible nor sensible to include all possible changes in th e error analysis, but rather certain 
requirements on the maximum allowable changes in 3a shall be specified. For the remaining deviations, a 
reasonable estimation that meets the following demands should be applied: 
 
⎯ simple and universally valid calculation, 
 
⎯ long-term drift is more important than short-term deviations. 
 
Both requirements are met by the standard deviation of the ambient temperature; therefore, the additional 
error is estimated by means of the standard deviation in aϑand the total uncertainty in aϑ can then be 
calculated by means of equation (18). 
 
a ta,δϑδϑ=  (18) 
 
6.3.1.2.4 Determination of the thermal capacity Cs of the entire store 
 
The net heating power supplied to the store is calculated by equation (19) 
 
) ( )(a s as, ei, p S ϑϑ ϑ ρ −×−Δ×××= UA c V Q&& (19) PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
22 © KEBS 2008 — All rights reserved  
The net heating power removed from the store is calculated by equation (20) 
 
) ( )(a s as, ei, p S ϑϑ ϑ ρ −× +Δ×××= UA c V Q&&   (20) 
 
 
The measured net store heat input or output during the time (equation (21)) is obtained by integration of equation (19) or (20) 
 
Q
S,m(tx) = dtsQxt
to×∫&  (21) 
 
The measured store capacity Cs,m is the difference between the amounts of heat at one steady-state (store 
temperatures,1ϑ) and another one (store temperatures,2ϑ) divided by the change in store temperature 
(equation (22)). 
 
Cs,m = ()∫ −=××−minst,
os,1 s,2minst,ms,
s
s,1 s,21t
tt QdtQϑϑ ϑϑ& (22) 
 
NOTE In this Kenya Standard, the total heat amount supplied to the store is counted positive and the total heat amount extracte d 
from the store or transferred (lost) to the ambient is counted negative. 
 
The error in the net amount of heat supplied to the store at charge (x=C) or extracted from the store at 
discharge (x=D) is calculated from 
 
[]5.02
as,2
XS, S ) () ( Q Q Q& &&δ δδ + =  (23) 
 
where 
 
⎥⎥
⎦⎤
⎢⎢
⎣⎡
+ΔΔ++×=
VV
cc
Q QS &&&&δ
ϑϑδδ
ρδρδ
ei,ei,
pp
xs,  
 
() ( ) () ()a s as, a s as, S,2 δϑδϑ ϑϑ δδ −×+−× = UA UA Q&  
 
If (UA)s,a has been determined at steady-state conditions after or before a temperature change by steps, it 
can be assumed that the errors in the heat loss capacity rate and the heat input to the store under steady-state conditions are approximately equal. Hence, the error in the net heat input to the store is approximately 
equal to the error in the heat loss of the store. In that case one of the two factors in equation (23) can be 
neglected.  
The error in the net heat input to the store is given by 
 
() dtQ t Qt
t×=∫×
os cms, δ δ  (24) 
 
The error in the measured store capacity is determined by the following equation: 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 23 ⎥⎥
⎦⎤
⎢⎢
⎣⎡
−+−+ ×=
s,1 s,2s,2
s,1 s,2s,1
ms, ms, ms,ϑϑδϑ
ϑϑδϑδ δ Q C C  (25) 
 
The temperature difference required between two steady states can be provided by charging or discharging 
the store. Regarding Test A as described under 6.3.1.1, the store capacity Cs can be determined twice, i.e. 
from the charge test (test phase A2) and from the discharge test (test phase A3). 
 
Theoretically, it can be assumed, that the thermal capacity of the entire store determined from a charge test 
(Cs.C) is equal to the thermal capacity of the entire store determined from a discharge test (C s,D). In reality 
there will be a differencebetween both capacities, due to measurement and evaluation errors. Hence this test 
sequence enables also a check of the measurement technique and the evaluation method. If the difference 
between Cs,C and Cs,D exceeds 3 % (related to the mean value of Cs,C and Cs,D) the test is not valid. 
 
The thermal capacity of the entire store Cs is calculated by the following equation: 
 
Cs = 2Ds, cs,C C+ (26) 
 
6.3.1.2.5 Determination of the stand-by heat loss capacity rate ( UA)sb,s,a 
 
The heat loss of the store occurred during the stand-by period tsb is calculated by equation (27) 
 
ms2, ms1, sb1, Q Q Q −=  (27) 
Where 
 
Qs1,m is the energy of the store at the start of the stand-by period 
 
Qs2,m is the energy of the store at the end of the stand-by period. 
 
Qs1,m and Q S2, m are calculated by equation (21). 
 The stand-by heat loss capacity rate is calculated by equation (28) 
 
()()
() ⎟⎟
⎠⎞
⎜⎜
⎝⎛
−−−⋅−=
sba, s1ssb1, sba, s1s
sbs
as,sb, lnϑϑϑϑ
CQ C
tCUA  (28) 
 
 
where  
C
s is the thermal capacity of the entire store calculated by equation (26) 
s1ϑ is the store temperature at the start of the stand-by period 
 
sba,ϑ the average value of the ambient temperature over the stand-by period. 
 6.3.1.2.6 Determination of the heat transfer capacity rate of immersed heat exchangers 
 
Figure 4 shows the temperature variations 
iC,ϑand C,0ϑobserved before, during and after the transient 
described in test phase H2 (see 6.3.1.1.3). Two characteristic times are of importance: t0, just before the 
transient, and as soon as a quasi-steady state with slow increase of all temperatures can be determined. 
 
NOTE  Typically t1 – t0 is approximately 1.5 min and the temperature increase of the heated store in this time interval is less than 2 % 
of mϑΔ . The mean logarithmic temperature difference is defined according to equation (29). For the smallest storage devices which are  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
24 © KEBS 2008 — All rights reserved equipped with heat exchangers of high nominal power, the temperature increase is greater than 2 % ofmϑΔ ; these facts restrict the 
accuracy of the test procedure. 
 
 
 
Key 
1 Time 
Figure 4–Temperatures ()tiC,ϑ  and ()tC,0ϑ observed before, during and after the transient described in 
test phase H2 
 
The store temperature near to the heat exchanger sϑ is ().0iC,tϑ . This temperature is also equal to ()⋅0 C,0tϑ  
 
The mean logarithmic temperature difference of the heat exchanger is 
 
() ()
() ()
() () ⎟⎟
⎠⎞
⎜⎜
⎝⎛
−−−=Δ
0iC, 1 C,00iC, 1iC,1 C,0 1iC,
m
lnt tt tt t
ϑ ϑϑϑϑϑϑ  (29) 
 
The heat transfer capacity rate of the heat exchanger is then  
(UA)
hx,s = () ()() ()()
() () ⎟⎟
⎠⎞
⎜⎜
⎝⎛
−−××=Δ− ×
0iC, 1 C,00iC, 1 C,0
p C
m1 C,0 1iC, p Clnt tt tc mt t c m
ϑ ϑϑ ϑ
ϑϑϑ&&
 (30) 
 
6.3.2 Determination of store parameters by means of parameter identification 
 
The store is tested on the test stand by different specific test sequences. The sequences are specified so as 
to stimulate the physical effects which correspond to the parameter to be determined. The measuring data 
are evaluated by parameter identification program using a store model.  6.3.2.1 Test sequences 
 
This clause describes the thermal test sequences for the different groups of stores. 
 
6.3.2.1.1 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 5 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 25  
Table 5 ―Compilation of the test sequences 
 
Purpose of test 
 Test Clause 
Determination of the store volume, the heat 
transfer capacity rate of the lowest heat 
exchanger and the thermal stratification during 
discharge. Test C 
group 1 
group 2 
group 3 
group 4  
6.3.2.1.2.1 
6.3.2.1.2.2 
6.3.2.1.2.3 
6.3.2.1.2.4 
Determination of the ther mal stratification during 
discharge with a ‘high’ flow rate Test S 
 6.3.2.1.3 
Determination of the heat loss capacity rate of the 
entire store during stand-by Test L: 
group 1 group 2 
group 3 
group 4  
6.3.2.1.4.1 6.3.2.1.4.2 
6.3.2.1.4.3 
6.3.2.1.4.4 
Determination of the heat transfer 
capacity rate and the position of the auxiliary heat 
exchanger(s) Test NiA for stores with auxiliary 
heating elements  6.3.2.1.5 
Determination of the position and length of the 
electrical heating element(s) Test NiA for stores with electrical heating elements 6.3.2.1.6 
Determination of the degradation of thermal 
strafication during stand-by Test NiA and Test NiB for stores of group 1 and 3 
 
Test NiA and Test NiB for stores Of group 2 and 4 
 Test EiA and Test EiB for stores with 
electrical auxiliary heating elements 
only. 6.3.2.1.7.1 
6.3.2.1.7.1 
 
6.3.2.1.5 6.3.2.1.7.2 
 6.3.2.1.6 
6.3.2.1.7.3 
 
 
NOTE 1 The exact vertical positions of the temperature sens ors as well as the upper connections of the heat exchangers above wh ich 
the store is charged mixedly, have a minor influenceon 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 manufactur ers 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. 
 
6.3.2.1.2 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 vo lume, 
or the thermal capacity of the entire store, determined according to this clause. This effect is to be explained by the long ch arging period 
which is necessary to achieve steady-state conditions and during  which the fluid in the dead volume is heated due to heat condu ction. 
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. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
26 © KEBS 2008 — All rights reserved  
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. 
 
6.3.2.1.2.1 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 3Co = 55 °C 
 
⎯ Test phase C3: discharging until steady-state is reached 
 
Table 6 — Flow rates and store inlet temperatures for Test C (group 1) 
 
Test 
phase 
 
 Process charge circuit discharge circuit 
 
C~
V& 
l/h 
 iC,~ϑ 
°C 
 ϑ C,0~ϑ 
°C D~
V& 
l/h iD,ϑ 
°C 
 D,0~ϑ 
°C 
C1 conditioning 0 ― ― 0.5 x nν& 20.00 variable 
C2 
 charge 0.5 xnν& 60.00 variable 0 
 ― ― 
C3 
 discharge 0 ― ― 0.5.× nν& 20.00 variable 
 
6.3.2.1.2.3 Group 2  
The goal of this test is the determination of the effective store volume, the heat transfer capacity rate of the 
charge heat exchanger and the stratification during discharge with a relatively 'low' flow rate.  
Test C (group 2): 
 
⎯ Test phase C1: conditioning until steady-state is reached 
 
⎯ Test phase C2: charge with constant charge power of  Pc = 1.0 • Pn untilC,0ϑ= 60 °C 
 
⎯ Test phase C3: discharge until steady-state is reached PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 27  
Table 7 ― Flow rates and store inlet temperatures for Test C (group 2) 
 
Test phase process charge circuit discharge circuit 
  
 C~
V& 
l/h iC,ϑ 
°C 
 C,0~ϑ 
°C DV~& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
C1 conditioning 
 0 ― ― 0.5 × nν& 20.00 variable 
C2 charge 1.2 × nν& 
 60.00 variable 0 ― ― 
C3 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 
6.3.2.1.2.3 Group 3 
 
Test C (group 3): 
 
⎯ Test phase C1: conditioning until steady-state is reached 
 
⎯ Test phase C2: charge until C,0ϑ= 55 °C 
 
⎯ Test phase C3: discharge until steady-state is reached 
 
Table 8 — Flow rates and store inlet temperatures for Test C (group 3) 
 
Test phase Process 
 charge circuit discharge circuit 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C 
 D,0~ϑ 
°C 
C1 conditioning 
 0 ― ― 0.5 × nν& 20.00 variable 
C2 charge 0.5 × nν& 60.00 variable 0 ― ― 
C3 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 
6.3.2.1.2.4 Group 4 
 
The goal of this test is the determination of the effective store volume and the heat transfer capacity rate of 
the discharge heat exchanger with a relative 'low' flow rate. 
 
The thermal stratification during discharge can, of course, only be assessed if the store is discharged 
stratified 
 
Test C (group 4): 
 
⎯ Test phase C1: conditioning until steady-state is reached 
 
⎯ Test phase C2: charge with constant charge power of n C~0.1~P P×= until 
C,0ϑ= 60 °C. 
 
⎯ Test phase C3: discharge until steady-state is reached 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
28 © KEBS 2008 — All rights reserved  
Table 9 — Flow rates and store inlet temperatures for Test C (group 4) 
 
Test phase Process charge circuit discharge circuit 
 
   
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C 
 D,0~ϑ 
°C 
C1 conditioning 
 0 ― ― 0.5 × nν& 20.00 variable 
C2 charge 1.2 × nν& 
 variable variable 0 ― ― 
C3 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 
 
6.3.2.1.3 Determination of the thermal stratification during discharge with a 'high1 flow rate (TEST S) 
 
For some stores of group 1 and 2, the thermal stratification during discharge and/or the draw off profile (plotted over the number of the withdrawn store volumes) may depend on the draw off flow rate. The goal of this test is to determine the thermal stratifica tion during discharge with a 'high' flow rate. 
 
Test S shall only be performed when it is determined by Test C that the store is discharged stratified. 
 Test S: 
 
According to Test C specified in 6.3.2.1.2, but with a discharge flow rate of 
n DV V&&=, but not less than 600 l/h. 
 
6.3.2.1.4 Determination of the stand-by heat loss capacity rate of the entire store (TEST L) 
 
The goal of this test is the determination of the heat loss capacity rate of the entire store during stand-by. 
Under consideration of note 2 in 6.3.2.1, the same operating conditions for the heat exchanger as in Test C 
shall be used. 
 
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.  
6.3.2.1.2.1 Group 1 
 
Test L: 
⎯ Test phase L1: conditioning until steady-state is reached 
 
⎯ Test phase L2: charge until ,C,0ϑ =55 °C 
 
⎯ Test phase L3: 48 hours stand-by 
 
⎯ Test phase L4: discharge until steady-state is reached 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 29 Table 10 — Flow rates and store inlet temperatures for Test L (group 1) 
 
Test 
phase Process charge circuit discharge circuit 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
L1 conditioning 
 0 
 ― ― 0.5 ×nν& 20.00 variable 
L2 charge 0.5 × nν& 60.00 variable 
 0 ― ― 
L3 stand-by 
 0 ― ― 0 ― ― 
L4 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 
 
6.3.2.1.4.2 Group 2 
 
Test L: 
 
⎯ Test phase L1: conditioning until steady-state is reached 
 
⎯ Test phase L2: charge with constant charge power of n C~0.1~P P×= until 
C,0ϑ= 60 °C 
 
⎯ Test phase L3: 48 hours stand-by 
 
⎯ Test phase L4: discharge until steady-state is reached  
 
 
Table 11 ― Flow rates and  storage device inlet temperatures for Test L (group 2) 
 
Test phase 
 
  
Process  charge circuit discharge circuit 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
L1 conditioning 0 
 ― ― 0.5 ×nν& 20.00 variable 
L2 charge 0.5 × nν& 60.00 variable 0 ― ― 
L3 stand-by 0 ― ― 0 ― ― 
L4 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 
6.3.2.1.4.3 Group 3 
 
Test L:  
⎯ Test phase L1: conditioning until steady-state is reached 
 
⎯ Test phase L2: charge until C,0ϑ= 55 °C 
 
⎯ Test phase L3: 48 hours stand-by 
 
⎯ Test phase L4:  discharge until steady-state is reached PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
30 © KEBS 2008 — All rights reserved  
Table 12 — Flow rates and store inlet temperatures for Test L (group 3) 
 
Test 
phase Process charge circuit discharge circuit 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
L1 conditioning 
 0 
 ― ― 0,5 ×nν& 20.00 variable 
L2 charge 0.5 × nν& 60.00 variable 
 0 ― ― 
L3 stand-by 
 0 ― ― 0 ― ― 
L4 discharge 0 ― ― 0.5 ×nν& 20.00 variable 
 
 
6.3.2.1.4.4 Group 4 
 
Test L: 
 
⎯ Test phase L1: conditioning until steady-state is reached  
 
⎯ Test phase L2: charge with constant charge power of n C~0.1~P P×= until 
C,0ϑ= 60 °C 
 
⎯ Test phase L3: 48 hours stand-by 
 
⎯ Test phase L4: discharge until steady-state is reached 
 
Table 13 ― Flow rates and store inlet temperatures for Test L (group 4) 
 
Test phase 
 process 
 charge circuit 
 discharge circuit 
 
 
   
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
L1 
 conditioning 
 0 
 ― ― 0.5 × nν& 20.00 variable 
L2 
 charge 
 1.2 × nν& 
 variable variable 0 
 ― ― 
L3 
 stand-by 
 0 ― ― 0 ― ― 
L4 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 6.3.2.1.5 Determination of the heat transfer capacity rate and the position of the auxiliary heat exchanger(s) (TEST NiA ) 
 
NOTE 1 If there is more than one additional heat exchanger, i indicates the number of the heat exchanger. 
 
NOTE 2 The exact position of the upper connection of an upper (auxiliary) heat exchanger is important, if it is near to the top  and 
causes a thermal stratification inside the store. The determination of this position by means of the test method described belo w is only in 
that case possible. 
 
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. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 31  
The connections of the auxiliary heat exchanger the heat transfer capacity rate of which shall be determined 
shall be fitted to the charge circuit of the testing stand according to the manufacturer's instruction. 
 
Test NiA: 
 
⎯ Test phase NiA1: conditioning until steady-state is reached 
 
⎯ Test phase NiA2: charge with constant charge power of n C~0.1~P P×= until temperature at the 
auxiliary heating sens or is equal 60 °C 
 
⎯ Test phase NiA3: discharge until steady-state is reached 
 
Table 14 ― Flow rates and store inlet temperatures for Test NiA (group 2 or 4) 
 
Test phase process charge circuit discharge circuit 
 
   
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
NiA1 
 conditioning 
 0 
 ― ― 0.5 × nν& 
 20.00 
 variable 
 
NiA2 
 charge 
 1.0 × nν& 
 variable 
 variable 
 0 
 ― ― 
NiA3 
 discharge 
 0 
 ― ― 0.5 × nν& 20.00 variable 
 6.3.2.1.6 Determination of the position (s) and length(s) of the electrical heating sources(s) (TEST EiA) 
 
The determination of the (vertical) position(s) of the electrical heating sources(s) is necessary if it/they are 
installed horizontally. 
 The length (as a model parameter) of the electrical heating source(s) shall be determined, if it/they is/are 
installed vertically in the top of the store. 
 This test applies only to stores with electrical heating sources(s). 
 
NOTE If there is more than one electrical heating source, i indicates the number of the heating source. 
 
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 charging connections shall be closed and all charging heat exchangers shall be filled with water. The 
closed connections shall be insulated in the same way as the store. 
 
Test EiA: 
 
⎯ Test phase NiA: conditioning until steady-state is reached 
 
⎯ Test Phase EiA2: charge with the nominal electrical power (specified by the manufacturer) until the 
heater is switched off by the thermostat ( ϑset = 60 °C) 
 
⎯ Test phase EiA3: discharge until steady-state is reached  
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
32 © KEBS 2008 — All rights reserved  
Table 15 ― Flow rates and store inlet temperatures for Test EiA 
 
Test phase 
 process 
 charge circuit discharge circuit 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
EiA1 
 conditioning 
 0 
 ― ― 0.5 × nν& 20.00 
 variable 
 
EiA2 
 charge 0 ― ― 0 ― ― 
EiA3 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 
6.3.2.1.7 Determination of the degradation of thermal stratification during stand-by 
 
A parameter describing the degradation of thermal stratification during stand-by shall only be determined, if 
stratification occurs during usual operation (e. g. for a store of group 4 that is charged and discharged mixed, 
this parameter can not be determined).  
To obtain this parameter, the upper (auxiliary) part of the store is charged and discharged twice in the same 
way. The first time the discharge is performed immediately after charging, the second time a stand-by of 24 
hours is included. The determination of the parameter describing degradation of thermal stratification during 
stand-by is based on the 'comparison' of the two draw off profiles by means of parameter identification.  
6.3.2.1.7.1 Group 1 and Group 3 (TEST NA and TEST NB) 
 
The test of stores of group 3 is only necessary, if they enable a stratified discharge. 
 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 auxiliary part of the store shall be fitted to the charge 
circuit of the testing stand.  
Test NA: 
 
⎯ Test phase NA1: conditioning until steady-state is reached 
 
⎯ Test phase NA2: charge until the integrated flow rate CV& = 0.5 × Vn 
 
⎯ Test phase NA3: discharge until steady-state is reached 
 
Table 16 ― Flow rates and storage device inlet temperatures for Test NA (group 
1 and 3) 
 
Test 
phase process charge circuit discharge circuit 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
NA1 conditioning 0 ― ― 0.5 × nν& 20.00 variable 
NA2 
 charge 
 0.5 × nν& 60.00 variable 0 ― ― 
NA3 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 33 Test NB: 
 
⎯ Test phase NB1: conditioning until steady-state is reached 
 
— Test phase NB2: charge until the integrated flow rate CV& = 0.5 × Vn 
 
⎯ Test phase NB3: 24 hours stand-by 
 
⎯ Test phase NB4: discharge until steady-state is reached 
 
Table 17 ― Flow rates and store inlet temperatures for Test NB (group 1 and 3) 
 
Test phase process charge circuit discharge circuit 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
NA1 conditioning 0 ― ― 0.5 × nν& 20.00 variable 
NA2 charge 0.5 × nν& 60.00 variable 0 ― ― 
NA3 stand-by 0 ― ― 0 ― ― 
NA4 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 
6.3.2.1.7.2 Group 2 and Group 4 with an auxiliary heat exchanger (TEST NB) 
 
The test of stores of group 4 is only necessary, if they enable a stratified discharge. 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 heat exchanger which enable a charge of the auxiliary part of the store, shall be connected to the charge 
circuit of the testing stand. 
 
NOTE Test NA has already been performed according to 6.3.2.1.5. 
 
Test NB: 
⎯ Test NB 1: conditioning until steady-state is reached 
 
⎯ Test phase NB2: charge with constant charge power of Pc = 2.0 • Pn until the temperature at the 
position of the auxiliary heating sensor is 60 °C 
 
⎯ Test phase NB3: 24 hours stand-by 
 
⎯ Test phase NB4: discharge until steady-state is reached 
 
Table 18 — Flow rates and store inlet temperatures for Test NB (group 2 and 4) 
 
Test phase process charge circuit discharge circuit 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
NB1 conditioning 0 ― ― 0.5 × nν& 20.00 variable 
NB2 charge 1.0 × nν& variable variable 0 ― ― 
NB3 stand-by 0 ― ― 0 ― ― 
NB4 discharge 0 ― ― 0.5 × nν& 20,00 variable 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
34 © KEBS 2008 — All rights reserved 6.3.2.1.7.3 Stores with electrical heat sources 
 
This test shall only be performed if an  electrical auxiliary heater is used. 
 
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 charging connections shall be closed and all charging heat exchangers shall be filled with water. The 
closed connections shall be insulated in the same way as the store. 
 
Test EB: 
 
⎯ Test phase EB1: conditioning until steady-state is reached 
 
⎯ Test phase EB2: charge with the nominal electrical power (according to the manufacturer's 
instructions) 
 
⎯ Test phase EB3 24 hours stand-by 
 
⎯ Test phase EB4: discharge until steady state is reached 
 
Table 19 ― Flow rates and store inlet temperatures for Test EB 
 
Test phase 
 process 
 Charge circuit 
 discharge circuit 
 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
EB1 conditioning 0 ― ― 0.5 × nν& 20.00 variable 
EB2 charge 0 ― ― 0 ― ― 
EB3 stand-by 0 ― ― 0 ― ― 
EB4 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 
6.3.2.1.8 Test procedure for combistores 
 
Charging and discharging the entire store implies connections of the charge/discharge circuits to the 
uppermost and lowermost direct ports available at the tank. Full discharging is required for conditioning of the store and for the final discharge phase. Full charging is required for all discharge tests which require that the 
entire store is charged. 
 The series of the performed tests should comprise two tests which include stand-by periods. One test is for 
the entire store, to determine the heat loss capacity rate. The other test concerns only the part of the store 
which is heated up (usually the auxiliary heated part).This test is used to determine the degradation of 
thermal stratification during stand-by. The stand-by period should be such that the losses during this period 
are approximately half of the stored energy. For these two tests with stand-by periods, the same test should also be performed without a stand-by period. 
 Flow rates and power values are given as examples only. The chosen flow rate or power should be suited to 
the type of component which will be used with those connections. 
 
6.3.2.1.8.1 General charge direct (TEST CD) 
 
⎯ Test phase CD1: conditioning until steady-state is reached 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 35 ⎯ Test phase CD2: charging through test ports until C,0ϑ = 55 °C 
 
⎯ Test phase CD3: optional stand-by until approximately half stored energy is lost to ambient 
 
⎯ Test phase CD4: direct discharge of the entire store until steady-state is reached 
 
Table 20 ― Flow rates and store inlet temperatures for Test CD 
 
Test phase process charge discharge 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
CD1 conditioning 0 ― ― 0.5 ×nν& 20.00 variable 
CD2 charge 0.5 × nν& 60.00 variable 0 ― ― 
CD3 stand-by 0 ― ― 0 ― ― 
CD4 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 
NOTE If the ports are used with a boiler the operating temperature of which is greater than 60 °C (e. g. a wood boiler), a high er inlet 
temperature (iC,ϑ ) may be used. 
 
6.3.2.1.8.2 General charge indirect (TEST CI) 
 
⎯ Test phase C11: conditioning until steady-state is reached 
 
⎯ Test phase CI2: charge through test heat exchanger at constant power of n C~0.2~P P×= until 
C,0ϑ = 60 °C 
 
⎯ Test phase CI3: optional stand-by until approximately half stored energy is lost to ambient 
 
⎯ Test phase CI4: direct discharge of the entire store until steady-state is reached 
 
Table 21 ― Flow rates and store inlet temperatures for Test CI 
 
Test phase process charge discharge 
 
 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
CI1 conditioning 0 ― ― 0.5 ×nν& 20.00 variable 
CI2 charge 1.2 × nν& variable variable 0 ― ― 
CI3 stand-by 0 ― ― 0 ― ― 
CI4 discharge 0 ― ― 0.5 × nν& 20.00 variable 
 
If the heat exchanger is used at different flow rates, the test should be performed four times, using, if 
possible, the following different charging conditions: constant power Pn at high and low flow rates, as well as 
constant power 0.5 Pn at low and high flow rates. 
 
6.3.2.1.8.3 General discharge direct (TEST DD) 
 
⎯ Test phase DD1: conditioning until steady-state is reached 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
36 © KEBS 2008 — All rights reserved ⎯ Test phase DD2: charging of the entire store until C,0ϑ= 55 °C 
 
⎯ Test phase DO3: discharge through test ports until OD,ϑ = 30 °C 
 
⎯ Test phase DD4: direct discharge of the entire store until-steady state is reached 
 
Table 22 ― Flow rates and store inlet temperatures for Test DD 
 
Test 
phase  
 process 
 
 charge discharge 
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
DD1 conditioning 0 ― ― 0.5 xnν& 20.00 variable 
DD2 charge 0.5 ×nν& 60.00 variable 0 ― ― 
DD3 discharge 0 ― ― 0.5 ×nν& 20.00 variable 
DD4 discharge 0 ― ― 0.5 ×nν& 20.00 variable 
 
6.3.2.1.8.4 General discharge indirect (TEST Dl) 
 
⎯ Test phase DI1: conditioning until steady-state is reached 
 
⎯ Test phase DI2: charge of the entire store until oc,ϑ= 55 °C 
 
⎯ Test phase DI3: discharge through the test heat exchanger until 
OD,ϑ= 30 °C 
 
⎯ Test phase DI4: direct discharge of the entire store until steady state is reached 
 
Table 23 ― Flow rates and store inlet temperatures for Test Dl 
 
Test phase process charge discharge 
  
C~
V& 
l/h iC,~ϑ 
°C C,0~ϑ 
°C D~
V& 
l/h iD,~ϑ 
°C D,0~ϑ 
°C 
DI1 conditioning 0 ― ― 0.5 x nν& 20.00 variable 
DI2 charge 0.5 x nν& 60.00 variable 0 ― ― 
DI3 discharge 0 ― ― 0.5 x nν& 20.00 variable 
DI4 discharge 0 ― ― 0.5 x nν& 20.00 variable 
 
If the heat exchanger is intended for domestic hot water preparation, this test shall be performed three times 
under different discharge conditions. To each of these three discharge conditions the following two charge 
conditions shall apply: Store fully charged and auxiliary part charged. In all, six tests shall be performed. The 
following discharge conditions should apply: 
 
⎯ Low flow rate 
 
⎯ High flow rate PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 37 The test shall be repeatedly performed under following conditions: Intermittent discharge at high flow rate 
with 10 minutes discharge and 10 minutes stand-by. This test does not need to be performed if it can be 
assumed that the heat transfer capacity rate of the discharge heat exchanger will not be time dependent. 
 
6.3.2.2 Evaluation of the test sequences described according to 6.3.2.1 by means of parameter identification (fit) 
 When all necessary tests as described in 6.3.2.1 are performed, identification of store parameters shall be carried out, using a numerical store model that fulfils the requirements given in annex B and an adequate parameter identification algorithm that fulfils the requirements given in annex C. 
 
The store model shall meet the requirements of the benchmark tests given in annex B.  
For the parameter identification the measuring data can be compressed and/or converted to constant time 
steps. In both cases, the data records shall represent mean values for the corresponding time step. During charge and discharge, the time steps should not exceed 3 minutes. During stand-by, a maximum time step of 
15 minutes is allowed. 
 
For the fit the measured values of the inlet store temperatures, ambient temperature, flow rates and the 
power of the electrical heating source(s) shall be used as inputs. Since at the beginning of each test the store is always conditioned to 20 °C, no skip time is required. Hence the data used for fitting, shall start with the 
second test phase, and 
sϑ = 20 °C shall be used as initial temperature for the store model. 
 
All parameters which are determined by parameter identification shall be identified during one parameter 
identification process. 
 
For every time step during the fit for each connection ‘X’(X = C for charge and X=D for discharge), the 
absolute difference between the transferred measured and predicted power shall be calculated by 
 
ΔPx=mx, px, P P−  
 
where:  ) ( Ppx,0, ix, px, ϑϑ ρ −×××= Vcp&  
 
Px,m = ) (mo,x, ix,ϑϑ ρρ −××× Vc&  
 
 
The function f(t) which shall be minimized is the integral of the sum over all absolute power differences 
calculated by 
 
f(t) =∫∑Δ
txdtPx 
 
7 Store test combined with a system test according to ISO 9459-5 
 
The procedure is in principle similar to 6.3.2.1 except that the data are gained during a whole system test 
according to ISO 9459-5 with additional sensors in the collector loop. The use of additional sensors in the 
collector loop is, however, only allowed if the normal function of the system is not affected. 
 
⎯ Using measuring equipment according to ISO 9459-5, the following data shall be measured and 
recorded additionally to the measurements required by ISO 9459-5: 
 
⎯ The volumetric flow through the collector loop as well as the inlet temperature at the store or heat 
exchanger and the outlet temperature at the store or heat exchanger of the collector loop. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
38 © KEBS 2008 — All rights reserved ⎯ If the system is equipped with an integrated hot water auxiliary heating, the volumetric flow through the 
auxiliary loop as well as the inlet temperature at the store or heat exchanger and the outlet temperature 
at the store or heat exchanger of the auxiliary loop. 
 
⎯ If an immersed electrical auxiliary heater is fitted to the store, no additional measurements are 
necessary as Paux is already measured. 
 
For the determination of the store parameters by means of parameter identification see 6.3.2.2. 
 
8 Test report 
 
8.1 General 
 
The test report shall include: 
 
⎯ a detailed description and the technical data of the tested store (based on the manufacturer's instruction) 
 
⎯ the determined parameters and a description of them 
 
⎯ reference to the used store model (parameters for simulation) 
 
8.2 Description of the store 
 
The description of the store shall be based on the information provided by the manufacturer. 
 
a) General data:  
⎯ Manufacturer: 
⎯ Type: 
⎯ Year of construction: 
⎯ Serial number: 
⎯ Nominal volume: 
⎯ Description and drawing of the schematic design: 
 
b) Stored water:  
⎯ Volume: 
⎯ Material and corrosion protection (o nly in case of drinking +water): 
⎯ Maximum operation pressure: 
⎯ Maximum operation temperature: 
⎯ Thermal insulation: 
⎯ Diameter and type of connections: 
 
c) Electrical heating source(s):  
⎯ Voltage: 
⎯ Nominal heating power: 
⎯ Diameter and type of connection: 
 d) Heat exchanger(s):  
⎯ Volume: 
⎯ Material and corrosion protection (o nly in case of drinking water): 
⎯ Type of pipes (with/without ribs, coil etc.): 
⎯ Size of the area for heat transfer: 
⎯ Position inside the store: 
⎯ Maximum operation pressure: 
⎯ Maximum operation temperature: 
⎯ Diameter and type of connections: PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 39  
8.3 Test results  
NOTE 1 Some of the parameters used for the characterization of the thermal behaviour of the store are related to the used store  model. 
Therefore, information on these parameters and the store model should be provided. 
 
a) Geometrical data:  
⎯ Weight of the complete storage device (empty): 
⎯ Maximum height of the complete storage device: 
⎯ Maximum diameter of the complete storage device: 
 
b) Volumes: 
⎯ Volume of the stored water: 
⎯ Volume of the heat exchanger(s): 
 c) Thermal parameters: 
⎯ Thermal capacity of the entire store: 
⎯ Thermal capacity of appropriate parts of the store (e. g. auxiliary heated part): 
⎯ Stand-by heat loss capacity rate (optional: operating heat loss capacity rate): 
⎯ Parameter describing the degradation of thermal stratification during stand-by: 
⎯ Parameter describing the quality of thermal stratification during direct discharge: 
⎯ Heat transfer capacity rate ( UA)hx,s of the heat exchanger(s). The test conditions (fluid, 
temperatures, flow rate, transferred heating power) for the determination of the heat 
transfer capacity rate shall be  mentioned in the test report. 
 
NOTE 2 If a diagram of ( UA)hx,s s over the temperature is included in the test report, the transferred heating power at each point of the 
diagram should be indicated, if the transferred heating power varies for the different points of the plotted ( UA)hx, s values. 
 
In addition, the draw-off profiles for two different draw-off flow rates (e. g. from Test C and Test S) and the 
two draw-off profiles used for the determination of the parameter describing the degradation of thermal 
stratification during stand-by (e. g. from Test NiA and Test NiB or from Test EiA and Test EiB), should be 
included.  
8.4 Parameters for the simulation  
All parameters which are necessary to describe the th ermal behaviour of the store in combination with a 
suitable numerical calculation model shall be recorded. In addition to the parameters listed in 8.3, the following parameters are required:  
a) Data of the fluid (e. g. constant values for the density and the specific heat capacity) 
 
b) Position of the 
 
⎯ inlet and outlet connection(s) for direct charge and discharge 
⎯ inlet and outlet connection(s) of the heat exchangers 
 
c) Information on the ability for stratified charging/discharging PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
40 © KEBS 2008 — All rights reserved  
Annex A 
(normative) 
 
Requirements for the numerical store model 
 
A.1 General 
 
For the system performance characterization by means of component testing and whole system simulation, 
numerical models which are able to describe the thermal behaviour of the components are required. 
 This annex gives instructions for modeling the store, in  order to enable a uniform modeling of the hot water 
store. 
 
A.2 Assumptions 
 
In order to simplify the model, it is possible to use the following assumptions to describe the thermal 
behaviour of the store. 
 
⎯ Each component of the store (e.g. tank, heat exchanger) can be assumed to be isothermal in horizontal 
direction. 
 
⎯ Temperature inversion inside the tank, which means dzd/ϑ  < 0, can be removed by an appropriate 
algorithm at the end of a time step. 
 
⎯ The thermal capacity of the storage vessel can be neglected.  This capacity can be added to the thermal 
capacity of the stored water. 
 
⎯ The thermal capacity of the pipes of the heat exchanger(s) can be neglected. 
 
⎯ The physical effects of heat conduction in the water and the metal wall of the tank and the convection in 
the water can be lumped together in an effective vertical thermal conductivity. 
 
A.3 Energy balance 
 For models which are based on a finite difference method with segments (nodes) of equal capacities, the 
energy balance for a node (i) of the stored water is represented by equation (A.1). The index (i+1) indicates 
the node above (i) and the index (i-1) indicates the node below (i). 
 
The left member of equation (A.1) describes the temporary change of the internal energy. The heat transport caused by the mass flows through the number of ‘P’ double ports is represented by the first sum on the right 
member. The electrical auxiliary heater is treated as an internal heat source. The heat transfer between the 
nodes of the heat exchanger and the stored water is described by the third term. If there are more heat 
exchangers, additional terms shall be added. The fourth term represents effects which can be described by 
using an effective vertical thermal conductivity. The last term considers the heat loss to the ambient. 
 
() ()[]()()is, ihx,
hxshx,
hx,3
auxaux
1is, s.i 1 is, 1-is,1 sp,
pis, s
ncdpdtϑϑ ξ ϑϑξϑϑξϑ−× ×++−×+− ×× =×+ ∑UA
nQmd
NC&  
+ () ()[]()()am is,
kz,ka,s,
is, 1-is, is, 1is, effnϑϑ ϑϑϑϑ λ −× −−+−×××
Δ+UA
NZA (A.1) PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 41  
where 
A is the cross-section are of the stored volume 
 
Cs is the thermal capacity of the tank 
 
Cp is the specific heat capacity 
 
dpm& is the mass flow rate through double port p 
 
N is the number of vertical nodes 
 
naux is the number of nodes occupied by the electrical auxiliary heating element 
 
kz,Δnis the number of nodes occupied by zone k with the length zΔ 
 
nhx is the number of nodes occupied by the heat exchanger hx 
 
p is the number of double ports 
 
(UA)hx,s is the heat transfer capacity rate for the heat exchanger to the store 
 
(UA)s,a,k is the heat loss capacity rate for the zone k 
 
Z is the height of the store 
 
auxQ& is the heat flow from the auxiliary heating element 
 
ϑ is the temperature  
 
effλ is the effective vertical thermal conductivity 
 
The logical switches 1ξ are used in the following way: 
 
1ξ−= 1 if dpm&from bottom to top (upwards), otherwise 1ξ= 0 
 
1ξ−= 1 if dpm&from top to bottom (downwards), otherwise 2ξ=0 
 
1hx,3=−ξ  if node i of the tank is in contact with node i of heat exchanger hx, otherwise hx,3ξ= 0 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
42 © KEBS 2008 — All rights reserved  
Annex B 
(normative) 
 
Store model benchmark tests 
 
B.1 General 
 
The benchmark test in this annex shall ensure that the store model fulfils fundamental requirements. Hence, 
for simplified operating cases the results calculated by the model shall be compared with the analytical 
solutions of the differential equations.  
B.2 Temperature of the store during stand-by 
 
It is assumed that the store is fully mixed and supplied with a homogeneous insulation. 
 
The decrease of the temperature of the store during stand-by can be calculated by equation (B.1).  
()()
tCUA
e t ⋅−
⋅−+=
sas,
am 0 am )( ϑϑϑϑ  (B.1) 
 
The temperature as a function of time (0 ≤ t ≤ 400 h) shall be calculated by equation (B.1) ( analytical) and by 
the store model  (numerical) with the following parameters: 
 
⎯ constant ambient temperature: amϑ = 20 °C 
 
⎯ initial temperature: 0ϑ = 60 °C 
 
⎯ thermal capacity of the store (constant): Cs = 2.0 MJ/K 
 
⎯ heat loss capacity rate: ( UA)s,a = 7.0 W/K 
 
This benchmark test shall be considered as valid if the maximum difference between the temperatures 
calculated in an analytical and numerical way is less then 0.001K 
 
If the model is part of a simulation program which enables the use of different time steps, this benchmark test 
shall be carried out for time steps of min and 60 min.  
B.3 Heat transfer from heat exchanger to store 
 
 
Key 
1 Heat transfer rate ( UA)h1,s = 1667 W/K 
 
Figure B.1 ―Store considered as a twin tube heat exchanger  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 43 For the parameters given in Figure 4 the results of the analytical solution are listed in Table B.1. 
 
Table B.1 — Results of the analytical solution 
 
out1,ϑ  
°C out2,ϑ  
°C Q& 
kW 
20.391 43.202 16.165 
 
 
This benchmark test may be considered as valid if the maximum difference between the calculation in an 
analytical and numerical way is less than 0.2 K for the temperatures less than 1 % (based on the analytical 
solution) for the transferred power. 
 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
44 © KEBS 2008 — All rights reserved  
Annex C 
(normative) 
 
Benchmarks for the parameter identification 
 
This benchmark test shall ensure that the evaluation procedure based on parameter identification leads to 
acceptable results. 
 A set of test and verification sequences for a so lar domestic hot water store is available from: 
 
DIN Deutsches Institut für Normung e. V. 
Normenausschuß Heiz- und Raumlufttechnik (NHRS) 
Burggrafenstraße 6 D-10787 Berlin 
 Based on this data, the parameters of the store shall be determined by means of parameter identification.  Using the determined parameters, the verification test sequences shall be re-simulated. 
 
This benchmark test may be considered as valid if the fo llowing criteria for the acceptance of the test results 
are fulfilled: 
 For each sequence the measured and predicted (simulated) energies transferred through each charge and 
discharge connection shall be calculated separately. Periods used for conditioning at the beginning of the test 
sequence shall be excluded. 
 
For each connection 'x' (x=C for charge and x=D for discharge) the relative error in transferred energy 
,xεQ 
shall be calculated by 
 
% 100
mx,mx, px,
Qx, ×−
=QQ Q
ε  (C.1) 
 
 
If the relative error in transferred energy Qx,ε exceeds 3.0 %, than the test is considered as not valid. 
 
For each sequence the measured and predicted (simulated) heat power transferred through each charge and 
discharge connection shall be calculated separately. Periods used for conditioning at the beginning of the test 
sequence shall be excluded. 
 Every time step during the simulation for each connection V (x=C for charge and x=D for discharge) the 
absolute difference between the transferred and predicted heat power shall be calculated byThe mean deviation in transferred heat power shall be calculated by 
 
mx, px, x P P P −=Δ  (C.2) 
 
The mean transferred heat power shall be calculated by 
 
∑∫∑Δ
=Δ
xtx,txx
tdtP
P  (C.3) 
The mean transferred heat power shall be calculated by 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
© KEBS 2008 — All rights reserved 45 ∑∫∑
=
xtx,txx
tdtP
P  (C.4) 
 
The relative error in mean transferred heat power pεshall be calculated by 
 
% 100PP
p×Δε  (C.5) 
 
If the relative error in mean transferred heat power pεexceeds 3.0 %, then the test is considered as not 
valid. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1855-3:2008 
46 © KEBS 2008 — All rights reserved  
Bibliography 
 
[1] H.Dr ϋck,E. Hahne: 
Thermal Testing of Stores for solar Domestic Hot Water Systems , Final report from IEA Task 
XIV,Dynamic Component and System Testing Group, IEA Report no.T. 14.DCST.1A 
 
[2] H. Visser, H.A.L. Van Dijik: 
Test procedures for short Term Thermal Stores , Kluwer Academic puplishers, 
Dordrekt, Boston , London 1991, ISBN 0-7923-1131-0 
 
[3] IEA solar Heating and cooling Program, Task III: 
Performance Testing of solar Collector s, Reference and Calibration Heaters , Swedish Council for 
Building Research, ISBN 91-540-4501-0, January 1986 
 
[4] J.M. Suter, M. Brack: 
Development of a test procedure for immersed heat exchangers , TM-33-87-08 Eidgenössisches 
Institut fϋr Reaktorforschung, CH-5303 W ϋrenlinngen, Dezember 1987 
 
EN 809, Pumps and pump units for liquids ― Common safety requirements  
 IEC 60335-1, Safety of household and similar electrical appliances ― Part 1: General requirements  
 IEC 60335-2-21, Safety of household and similar electrical appliances — Part 2: Particular requirements for 
storage water heaters   
 KS 1855-1, Thermal Solar Systems and Components ― Custom Built Systems ― General Requirements  
 
EN 1717, Specifications for installation of potable water in drinking water installations and general 
requirements of devices to prevent pollution by backflow