1 Principle of the method
Method B
edited jen 9/6, 17:32
Heat balance of the generation sub-system, including control of heat generation
The performance of the thermal solar system will be determined by the following parameters:
-
collectors characteristics according to product standards (collector area, optical efficiency, loss coefficient, etc);
-
storage parameters (type of storage, sizing, etc); storage heat loss?
-
collector loop losses and transmission losses between storage and backup (length, insulation, heat exchanger
efficiency, etc);
-
running conditions (temperature differential; etc);?
-
climate conditions (sunshine, etc) ;
-
auxiliary energy of the solar pump;and controllers?
-
heat demand of the heat distribution system;
-
heat demand of the domestic hot water distribution system;.
The relevance of these effects on the energy requirements depends on:
-
the type of thermal solar equipment;
-
the location of the equipment;
-
the running conditions (temperature, control, sizing,…)
-
control strategy.
In order to respect the general structure of the system loss calculation, the performance of the thermal solar
subsystem shall be characterised by the following input data:
-
the type and characteristics of the thermal solar system;
-
the location and orientation of the thermal solar system (weather data);
-
the type of the control system;?
-
the heat requirement.
This standard needs input data coming from other parts of the system energy requirement calculation prEN 14335.
Based on these data the following output data are calculated in the thermal solar subsystem module:
-
the thermal energy generated by the thermal solar system Q out,s;
-
the thermal losses of the collection loop;
-
the auxiliary consumption W s;
-
the recoverable and recovered auxiliary energy W r,s,W nr,s;
-
the recoverable thermal losses of the collection loop.
Figure 1 shows the calculation inputs and outputs of the thermal solar subsystem.
Ws
Qbu,s
Wnr,s (=0)
Wr,s
Qout,hw
Qin,s=Hc
Solar thermal system
Qout,sh
Ql,s
Ql,r,s
Ql,nr,s
Figure 1: Thermal solar subsystem
where:
Ws
auxiliary energy required by the thermal solar subsystem (solar pumps, controllers, etc.).
Qbu,s thermal input energy from back-up loop
Qout,s heat supplied to the distribution systems (heat and DHW)
Qin,s
thermal energy generated by the thermal solar system
Ql,g
the thermal losses of the loop between the solar tank and the back up
Ql,r,s
recoverable losses of the of the loop and the auxiliary energy required by the thermal solar subsystem
Ql,nr,s the unrecoverable losses of the thermal solar subsystem
Thermal energy generated by the thermal solar system and solar fraction
The thermal energy generated by the thermal solar system is determined by the calculation of the solar fraction, F.
The solar fraction take already into account thermal solar system losses as the heat losses from collector loop and
storage.
The energy generated by the thermal solar system is calculated by:
Qout,s = F x Qin,d
where:
Qin,d
heat and/or hot water demand
[Wh]
(eq 1)
F
solar fraction i.e. part of the demand covered by the solar system, F = Q out,s/Qin,d, formula for calculating F is
given in eq.?
Back-up energy, Qbu,s
The energy which must be delivered by other generation systems (back-up systems) is the difference between the
energy demand and the energy delivered by the solar system:
Qbu,s = Qin,d - Qout,s
[Wh]
(eq 2)
Heat losses between the thermal solar system and the backup are added to the load of the other generation
systems.
Auxiliary energy Ws
Auxiliary energy is in some cases needed to operate the thermal solar subsystem:
- electricity for the pump(s) is considered totally absorbed in the thermal solar subsystem and from there partly
passed on to the losses (50/50?)
- electricity for controller(s) is converted to heat loss
Recoverable, recovered and unrecoverable heat losses
The losses, that are calculated, are not necessarily lost. They are partly recoverable losses, and a part of these
recoverable losses are really recovered. The part of the recovered losses is determined by the localisation of the
thermal solar subsystem and the utilisation factor (depending on the gain/loss ratio and the time constant of the
building, see 9.2 in EN ISO 13790). The recoverable heat losses Qrl,s are the indoor heat losses from the solar
thermal system.
Calculation periods
The objective of the calculation is to determine the yearly primary energy demand of the heating system. To do this
monthly calculations periods are use
2 Thermal solar system calculation
Calculation procedure
Calculations are carried out for each month and each heating phase.
They involve the following stages:

Calculating solar fraction and solar output for heating and/or hot water

Calculating transmission losses for the solar installation (between storage and backup)

Calculating backup storage losses

Calculating consumption of solar installation auxiliaries

Calculating potential recoverable losses
5.1 DETERMINATION OF SOLAR FRACTION
The general formula for the solar fraction is1:
F = ctype ( aY + bX + cY² + dX² + eY3 + fX3 )
[-]
(eq 4)
where:
ctype
storage type correction coefficient (two storage types: 1: water storage; 2: building/floor storage).
The values of cW are defined in the national annex. If no national values are specified, default
values are given in annex B chapter B1
[-]
a, b, c, d, e, f
correlation coefficients depending also on storage type. The values are defined in the national
annex. If no national values are specified, default values are given in annex B chapter B2.
X
ratio between standard collection losses and requirements (see eq. 8)
Y
ratio between the solar energy absorbed and requirements (see eq. 9)
If the result is negative, F =0, if it is greater than 1, F = 1.
5.1.1 Case of factory made solar domestic hot-water heaters (system test):
X = AC*. Uc*.ΔT.tmois. cOS / Q
[-]
(eq 5)
Y = AC*.ISC.
[-]
(eq 6)
mois
/Q
Where :
AC*
equivalent collection surface area (thermal properties are intermediate parameters used in EN 12976-2 but
not indicated on the official test results). If the thermal properties of the hot-water heater are not known,
penalty default values are adopted (see annexe B chapter B3)
[M2]
U C*
coefficient of collection losses (thermal properties are intermediate parameters used in EN 12976-2 but not
indicated on the official test results). If the thermal properties of the hot-water heater are not known, penalty
default values are adopted (see annexe B chapter B3)
[W/m².K]
5.1.2 All other cases (collector test):
X = A. UC.ηloop. tsh.ccap / Q
[-]
(eq 8)
Y = A.η0. ηloop.ISC tsh /Q
[-]
(eq 9)
Where:
A
surface area of the collectors according EN 12975-2
UC
coefficient of thermal loss of the collection loop. It is obtained by.
UC = a1 + UL/A
[m²]
[W/m².K]
Where :
a1 coefficient of primary thermal losses from the collector test standard EN 12975-2. Default values are
given in annex B chapter B8
[W/m².K]
UL thermal losses coefficient of pipes in the collector circuit obtained by multiplying the length of the pipes
by the heat loss coefficient per meter of pipe. If no calculation is carried out, UL is taken as UL = 5 + 0.5
A [W/K]
η0
optical efficiency from the collector test standard EN 12975-2. Default values are given in annex B chapter
B9
ηloop
efficiency of the collector loop taking into account influence of heat exchanger and thermal losses from the
loop.The values are defined in the national annex. If no national values are specified, default values are
given in annex B chapter 10
ΔT
reference temperature differential
used to calculate standard collector losses
refe
[K]
where:
e average outside temperature for the considered period, values given in national annex
1
formula borrowed from the f-chart rule (note:GIVE REFERENCE?)
(eq 7)
[°C]
ref reference temperature depending on application and storage type, values defined in the national
annex. If no national values are specified, default values are given in annex B chapter B4
tsh
length of the monthly sunshine in hours. The values are given in the national annex.
ccap
storage capacity correction coefficient. The values are defined in the national annex. If no national values are
specified, default values are given in annex B chapter B6
Q
requirements. Q is equal to Qhw when calculating solar fraction of hot water requirements and Qsh when
calculating solar fraction of heating requirements.
[WH]
ISC
average solar irradiance on the flat surface of the collectors during the considered period. The values are
defined in the national annex. If no national values are specified, default values are given in annexe B
chapter B7
[W/m2]
5.1.3 Calculating solar fraction and output for heating and/or hot water
Only domestic hot water production
In this case the solar fraction is calculated only with the characteristics of the domestic hot water system.
Only space heating production
In this case the solar fraction is calculated only with the characteristics of the heating system.
Combined systems (domestic hot water and heating)
In a combined system, the solar fraction Fhw of the hot water requirements and the solar fraction Fsh of the heating
requirements are both calculated.
The general formula (eq4) applies, assuming that part of the collection surface area is used for heating and the
other part is used for hot water each month, in proportion to heating and hot-water requirements. In the preceding
formulae for parameters X, Y and COS, the collector area is multiplied by the coefficient Parsh in order to calculate
solar fraction of heating requirements and by the coefficient Parhw in order to calculate solar fraction of hot-water
requirements.
Parsh = Qsh / (Qsh + Qhw)
[-]
(eq 10)
Parhw = Qhw / (Qsh + Qhw)
[-]
(eq 11)
The solar output is then:
Qout,s = Fhw*Qhw + Fsh*Qsh
The overall solar fraction is
F = Qout,s/(Qhw+Qsh)
5.2 CALCULATING HEAT LOSSES FROM TRANSMISSION BETWEEN SOLAR TANK AND BACK-UP
The transmission heat losses between the solar tank and the backup are calculated as stated in the national annex
or as shown in annex B11.
5.X HEAT LOSSES FROM COLLERTOR LOOP
The transmission heat losses from collector loop are accounted for in the efficiency factor of the collector loop, ηloop.
5.X HEAT LOSSES FROM SOLAR TANK
The heat losses from the solar tank are accounted for in calculation of F? (note: NB)
5.3 BACKUP STORAGE LOSSES
The losses from the backup heat generator are not taken into account in this part of the standard, but are
determined in other parts depending on the type of the heat generator:
-
combustion systems: prEN14335-2.2.1
-
heat pumps: prEN14335-2.2.2
-
electrical heaters: ?
5.4 CONSUMPTION OF SOLAR INSTALLATION AUXILIARIES
In case of a thermo siphon solar hot water heater (self-circulating solar system), consumption by auxiliaries is zero.
In case of a forced circulation system, pumps and controllers are taken into account.
5.4.1 Pumps
The consumption by pumps in the solar installation is calculated as follows.
W p = Pp.tp
[Wh]
(eq 12)
Where:
Pp
total nominal input power of pumps
[W]
tp
pump operation time (2000 hours per year distributed to monthly values corresponding to the distribution of
the monthly total solar output)
,obtained from the following formula: (JEN: product standard: 2000 hours)
Dfonc = Dens . min [ 1; ( Qsh + Qhw ) / (Isc . A . 0,4 . tmois ) ]
[h]
(eq 13)
This formula assumes that, in winter, when recoverable sunshine does not meet requirements, the primary pump
operates while the sun is shining. In summer, the pump operates in proportion to the ratio between requirements
and recoverable sunshine (estimated on the basis of average output from the solar captor of 40%).
Where Pp is not known
Pp = 50 + 5 A
[W]
(eq 14)
where
A
aperture area of the collectors
[m²]
5.4.2 Controllers
The consumption by controllers in the solar installation is calculated as follows.
W c = Pc.tc
[Wh]
(eq 12)
Where:
Pc
total nominal input power of controllers
[W]
tp
controller operation time (controller is ON all the time unless otherwise stated by manufacturer) [h]
Where Pc is not known
Pp = 10 + 1 A
[W]
where
A
aperture area of the collectors
[m²]
5.5 RECOVERABLE HEAT LOSSES
a) Auxiliary consumption
For the recoverable auxiliary energy loss it is distinguished between:
- pumps, - all auxiliary energy to pumps is considered totally recovered (and accounted for already in the
calculation of F) in the fluid of the solar system; 50% is considered lost again from there as heat loss
(eq 14)
- controllers, - all auxiliary energy to controllers is considered converted into heat loss
All heat losses in the heating season are considered 100% recoverable. (note: pumps and controllers assumed
situated indoor)
For all months in the heating season: Ql,r,p = Wp * 0,5
For all months out of the heating season: Ql,r,p = 0
b) Heat losses between the solar tank and the backup
All heat losses in the heating season are considered 100% recoverable. (note: pumps and controllers assumed
situated indoor; maybe indoor part to be specified?)
For all months in the heating season: Ql,r,b-u = Ql,s-bu (from B11)
For all months out of the heating season: Ql,r,b-u = 0
c) Heat losses from solar tank
All heat losses in the heating season are considered 100% recoverable. (note: pumps and controllers assumed
situated indoor; maybe indoor part to be specified?)
For all months in the heating season: Ql,r,st = Ql,st (note: from ?)
For all months out of the heating season: Ql,r,st = 0
d) Heat losses from collector loop
Heat losses from the collector loop are not considered recoverable. p(note to be discussed?)
e) Total recoverable generation heat loss
(note: summarize the above)
Annex A (informative)
Example
Annex B (informative)
Default values for parametering the calculation method
B1) Storage type correction coefficient cW
In the case of a water storage solar heating system or a solar hot-water system:
cW = 1
[-]
In the case of a “solar floor”, the values for cW are given in the table below, depending on the diameter and spacing
of the tubes:
Spacing of tubes
Diameter of tubes in mm
in cm
up to 17
18 to 22
23 to 27
28 or over
up to 17
1
1.01
1.03
1.04
18 to 22
0.98
1
1.01
1.03
23 to 27
0.96
0.98
1
1.01
28 or over
0.94
0.95
0.97
1
Table B1: Storage irrigation correction coefficient cW
If the spacing and diameter of the tubes are not known, the penalty value cW = 0.94 applies.
Similarly, in a system with several floors with different properties, the penalty value cW = 0.94 applies.
B2) Storage-driven coefficients
Coefficient
Type of storage
Water storage
(domestic hot water
production)
Solar floor
a
1.029
0.863
b
-0.065
-0.147
c
-0.245
-0.263
d
0.0018
0.008
e
0.0215
0.029
f
0
0.025
Table B2: Storage-driven coefficients
B3) Penalty default values
If the thermal properties of the hot-water heater are not known, and only the surface area of the collectors A (m²)
and the nominal storage volume Vn (litres) are known, the following penalty default values are adopted:
Ac* = 0.4 A
A surface area of the collectors [m2]
UC* = 17 + 8/A [W/m².K]
B4) Standard temperature differential ΔT
rf is equal to:



17.2°C for heating with a solar storage floor
100°C for space heating with a storage tank
11.6 + 1.18uw + 3.86cw – 2.32e when calculating the solar fraction of hot-water requirements
with
uw
temperature of the hot water used for transfers taken as equal to 40°C
cw
temperature of the cold water entering the hot-water production system.
e
average outside temperature for the considered period
[°C]
B5) Length of the monthly sunshine in hours tmois
Jan
Feb
March
April
May
Jun
Jul
Aug
Sept
Oct
Nov
Dec
H1
48
87
149
126
145
188
276
256
175
107
42
50
H2
107
124
163
183
186
255
292
300
173
104
121
75
H3
116
78
204
235
305
282
340
283
228
196
210
153
Table B3: Monthly sunshine in hours
B6) Storage capacity correction coefficient ccap
In the case of water storage, the storage correction coefficient cOS is obtained from the following formula:
ccap
=(
Vref/VS)0.25
[-]
(eq B1)
Vref is a reference volume equal to 75 litres per m² of collector.
VS is the solar storage volume. In the case of hot-water heaters, the following formula applies:
VS = CS / ρw.cp
Where
CS
storage capacity EN 12976-2
ρw
density of the water
cp
specific capacity water
[litres] (eq B2)
(MJ/K)
(1 kg/l).
(0.00418 MJ/kg.K).
The VS solar storage volume VS can also be obtained from the following equation:
VS = Vn.(1 – faux)
[litres] (eq B3)
Where:
faux is the effective fraction accounted for by any integrated backup EN 12976-2. faux is zero when the tank does not
have an integrated backup.
Where the tank has an integrated backup, there are two options for determination of faux:
1) faux may be determined directly by tests according to European Norms
2) The volume heated by the backup (contained between the top of the tank and the bottom of the electric element
or exchanger: Vap is taken and the following formula applied:
faux = x. Vbu/Vn
[-] (eq B4)
where
x
management coefficient equal to
- 0.9 ?! if the backup is an electric element with a permanent power supply or an exchanger connected to a
boiler operating permanently,
- 0.6 otherwise (night backup or emergency backup).
The default value of faux is 0.5 for a vertical tank and 2/3 for a horizontal tank.
In the case of a solar floor, the storage correction coefficient ccap is obtained from the following formula:
ccap = (55 . A / Ap)0.03
[-] (eq B5)
where
A
surface area of the collectors
Ap
surface area of the solar floor
(note: should be based on the heat capacity of the floor?).
B7) Solar irradiance on the flat face of the collectors ISC
ISC is the average solar irradiance on the flat surface of the collectors during the considered period expressed in
W/m².
Three categories of orientation of collectors are possible:
1. Where collectors face between south-east and south-west and are angled at between 40° and 50° (note: to
be changed to “ranging from latitude-20° till latitude+5°”) from the horizontal and are not masked by any
obstacles, the values for ISC are as given in the table below for the three climatic zones.
These values incorporate a reduction of approximately 6% to take account of the angle of incidence (the
efficiency of a glazed collector falls when the angle of incidence is different from the normal incidence). As
this reduction only applies to glazed collectors, the values given in the table must be divided by 0.94 for
non-glazed collectors.
Jan
Feb
Mar
H1
55
97
129
H2
91
123
H3
92
90
Apr
May
Jun
Jul
Aug
Sept Oct
Nov
Dec
140
156
178
212
199
157
106
49
43
138
175
178
204
221
214
165
108
97
59
168
200
240
224
248
213
191
162
154
115
Table B4: (Corrected average monthly solar irradiance values for south-facing glazed collectors (angle of
45°) (W/m²) (note: to be changed corresponding to the 4 data sets used in the product standards)
2. In all other cases, a coefficient, fISC of reduction of 0.8 is multiplied to the values in the table, provided that
the orientation of collectors is within the range of +/-90° of south (between east and west) and the average
height of obstacles on the horizon is less than 20° (tilt angle is arbitrary).
3. For all other configurations, no account is taken of the solar installation (no influence on the building energy
performance).
B8) Coefficient of primary thermal losses from the collector a1
The coefficients of losses a1 is determined in accordance with standard EN 12975-2. (W/m².K)
If the thermal properties of the collector are not known, the following penalty default values are adopted:
a1 = 10 W/m²K (glazed collector)
a1 = 30 W/m²K (unglazed collector),
B9) Collector optical efficiency η0
The optical output ratio η0 is determined in accordance with standard EN 12975-2. If the thermal properties of the
collector are not known, the following penalty default values are adopted:
η 0 = 0.6
B10) Efficiency of the collector loop ηloop,
The efficiency of the collection loop loop is 0.8. (note: documentation for the value 0,8? rather rough, dependence
on heat exchanger to be considered – recommendations/guidelines for national annexes to be made )
B11) Calculating transmission losses between the solar tank and the backup
B11.1 Individual solar hot-water heater
In case of an integrated backup, losses are zero.
In case of separate backup the losses Ql,s-bu between the solar tank and the backup are calculated using the
following formula:
If the pipework is insulated:
Ql,s-bu = 0.02 Fhw . Qw
[Wh]
If the pipework is not insulated:
Ql,s-bu = 0.05 Fhw . Qw
Ql,s-bu = Fhw . ccap vsa . (θw,d-θamb).Nsubnor.np
Fhw
[Wh]
[Wh]
(eq B6)
rate of solar fraction for the hot water.
cw, θw,d, Nsubnor and np,
given in other chapters of the national standard .
vsa
volume of the pipework between the solar tank and the backup.
θamb
ambient temperature of the pipework. θamb is calculated by:
θamb = θi – b (θi – θe)
[°C]
(eq B7)
where
θi inside temperature during the normal period (°C),
θe outside temperature
b is the coefficient of reduction in temperature.
Where vsa is not known:
Ql,s-bu = 0.05 Fhw . Qhw
[Wh]
B11.2 Collective solar hot-water system with centralised backup
If the pipework is insulated:
Ql,s-bu = 0.02 Fhw . Qw
[Wh]
If the pipework is not insulated:
Ql,s-bu = 0.05 Fhw . Qw
[Wh]
B11.3 Collective solar hot-water system with individual backup ???
Where individual backups are linked to the solar tank by a looped network with the return in the solar tank, losses in
the looped network are not taken into account.
Otherwise:
If the pipework is insulated:
Qdwsa = 0.25 Fhw . Qw
[Wh]
If the pipework is not insulated:
Qdwsa = 0.4 Fhw . Qw
[Wh]
Annexe C (informative)
Product classification
Solar collectors
Properties are:
A
surface area A is the aperture area input surface area or overall surface area,
(m²),
η0
optical efficiency,
(-)
a1
coefficients of losses in accordance with standard EN 12975-2.
(W/m².K)
Solar hot-water heaters
This paragraph applies to factory made solar hot-water heaters classified as a unit (EN 12976).
Where no classification is given, a solar hot-water heater can be defined by its components:
- collector,
- tank,
- primary loop pipework.
A
surface area of the collectors
(m²)
Vn
nominal storage volume
(litres).
Note:
The following thermal properties are intermediate parameters used in EN 12976-2 but not indicated on the official
test results.
AC*
equivalent collection surface area
(m²)
CS
storage capacity
(MJ/K)
U C*
coefficient of collection losses
(W/m².K)
US
coefficient of storage losses (JZ: not used in the method?)
(W/K)
faux
effective fraction accounted for by the backup, EN 12976-2.
(-)
Storage tanks
Vn
nominal volume
(litres)
UA
(W/K).
coefficient of losses
If UA is not known but the cooling constant Cr (Wh/l.K.day) is, the following equation is used:
UA = Cr.Vn/24
[W/K]
Note:
The calculation method only applies if the cooling constant of the storage tank is less than or equal to the
default value of the hot-water tank, i.e.: Cr ≤ 4.2 Vn-0.45.
VS
solar storage volume, obtained from the following equation:
VS = Vn.(1 – faux)
Where:
faux is the effective fraction accounted for by any integrated backup EN 12976-2.
-
faux may be determined directly by tests carried out in accordance with Eropean Norms
-
faux is zero when the tank does not have an integrated backup.
[litres]