Where relevant, the source document for the definition is indicated in brackets.

auxiliary energy consumption, combined see combined auxiliary energy consumption

auxiliary heat source source of heat, other than solar, used to supplement the output provided by the solar heating system (ISO 9488:1999); in French, energie d’appoint; in German, Zusatzenergie auxiliary, long-running-time see long-running-time auxiliary

boiler a complete unit with burner, combustion chamber and exhaust-gas/water heat exchanger; in French, chandiere; in German, Heizkessel

burner the burner, with or without a combustion chamber, but not including the exhaust-gas/water heat exchanger

cell, photovoltaic see photovoltaic cell collector, solar (thermal) see solar (thermal) collector combined auxiliary energy consumption the sum of the final energy consumption of the auxiliary boiler and the primary energy consumption of the electrical heating element in a solar heating system

combined total energy consumption the sum of the combined auxiliary energy consumption and the primary parasitic energy consumption of a heating system

combisystem, solar see solar combisystem contribution, solar see solar contribution

drainback system a solar thermal system in which, as part of the normal working cycle, the heat transfer fluid is drained from the solar collector into a storage vessel when the pump is turned off, and refills the collector when the pump is turned on again (ISO 9488:1999)

energy consumption, combined auxiliary see combined auxiliary energy consumption

energy consumption, combined total see combined total energy consumption

energy, final see final energy

energy, parasitic see parasitic energy

energy, primary see primary energy

energy savings, fractional see fractional energy savings

energy, secondary see secondary energy

energy, useful see useful energy

final energy the energy supplied available to the consumer to be converted into useful energy (Energy Dictionary, 1992)

flow temperature (of a heat transfer fluid) temperature of the fluid before energy is removed (Energy Dictionary, 1992); in French, temperature de depart; in German, Vorlauftemperatur

forced-circulation system a solar heating system that utilizes a pump or a fan to circulate the heat transfer fluid through the collector(s) (ISO 9488:1999) fraction, solar see solar fraction

fractional energy savings reduction of purchased energy achieved by the use of a solar-plus-supplementary heating system, calculated as 1 – (auxiliary energy used by solar heating system/energy used by conventional heating system), in which both systems are assumed to use the same kind of conventional energy to supply the user with the same heat quantity giving the same thermal comfort over a specified time period (ISO 9488:1999). Note: the assumptions made in this handbook to calculate the fractional energy savings are given in Section 6.2

global (solar) radiation hemispherical solar radiation received by a horizontal plane. Note 1: approximately 99% of the global solar radiation incident at the Earth’s surface is contained within the wavelength range from 0.3—3 m.

Note 2: solar engineers commonly use the term ‘global radiation’ in place of ‘hemispherical radiation’. This use is a source of confusion if the referenced surface is not horizontal (ISO 9488:1999)

heat source, auxiliary see auxiliary heat source (heat) storage the action of storing heat in a heat store

(heat) store a device designed to maintain a balance between heat production and heat consumption by temporarily storing excess heat for later delivery

heating system system for the production of heat for any purpose; in French, installation de production de chaleur; in German, Heizanlage

heating system, solar see solar heating system heating system, space see space heating system

hemispherical (solar) radiation the solar radiation on a plane surface received from a solid angle of 2n sr (i. e. from the hemisphere above). Note 1: the tilt and the azimuth angles of the surface should be specified, e. g. horizontal.

Note 2: hemispherical solar radiation is composed of direct solar radiation and diffuse solar radiation (solar radiation scattered in the atmosphere as well as solar radiation reflected by the ground). Note 3: solar engineers commonly use the term ‘global radiation’ in place of‘hemispherical radiation’. This use is a source of confusion if the referenced surface is not horizontal (ISO 9488:1999) irradiance power density of radiation incident on a surface, i. e. the quotient of the radiant flux incident on the surface and the area of that surface, or the rate at which radiant energy is incident on a surface, per unit area of that surface. Irradiance is normally expressed in watts per square metre (W/m2) (ISO 9488:1999)

irradiation the incident energy per unit area of a surface, found by integration of irradiance over a specified time interval, often an hour or a day. Irradiation is normally expressed in megajoules per square metre (MJ/m2) (ISO 9488:1999)

long-running-time auxiliary in a solar combisystem, an auxiliary boiler designed to run for a long time at more or less fixed power, for example to burn wood efficiently in the form of logs

‘low-flow’ technology a way of designing and operating a solar heating system in which the mass flow rate in the collector loop is significantly lower than 30 1/h m2 .. . See Section

collector area

module, solar see solar module panel, solar see solar panel

parasitic energy electricity consumed by pumps, fans and controls in a solar heating system (ISO 9488:1999); in French, energie auxiliaire; in German, Hilfsenergie

photovoltaic cell semiconductor device that converts radiant energy (usually solar radiation) into electrical energy by means of the photovoltaic effect

primary energy energy that has not undergone any sort of conversion (Energy Dictionary, 1992)

radiation, hemispherical (solar) see hemispherical (solar) radiation

reference system the conventional heating system used for the calculation of the fractional energy savings; see fractional energy savings

return temperature (of a heat transfer fluid) temperature of the fluid after energy has been removed (Energy Dictionary, 1992); in French, temperature de retour; in German, Riicklauftemperatur

savings, fractional energy see fractional energy savings

secondary energy energy produced by the conversion of primary energy or of another secondary energy (Energy Dictionary, 1992); synonym of‘derived energy’

solar combisystem a solar-plus-supplementary heating system designed to supply heat to both a space heating system and to a domestic hot water system

solar contribution energy supplied by the solar part of a solar heating system. Note: the solar part of a solar heating system and any associated losses need to be specified, otherwise the solar contribution is not uniquely defined (ISO 9488:1999)

solar fraction energy supplied by the solar part of a solar heating system divided by the total system load. Note: the solar part of a solar heating system and any associated losses need to be specified, otherwise the solar fraction is not uniquely defined (ISO 9488:1999)

solar heating system system composed of solar collectors and other

components for the delivery of thermal energy (ISO 9488:1999); synonym of ‘solar thermal system’. In German, Solaranlage, not solares Heizsystem. Note: ‘solar heating system’ is used as a generic term that includes solar-only systems, solar pre-heat systems and solar-plus-supplementary systems

solar module smallest complete, environmentally protected assembly of interconnected solar cells

solar panel a group of solar modules fastened together

solar-plus-supplementary system a solar heating system that utilizes both solar and an auxiliary energy source in an integrated way and is able to provide a specified heating service independently of solar energy availability (ISO 9488:1999). Note: the auxiliary energy device is a part of the solar-plus­supplementary system, just as solar collectors are

solar radiation, global see global (solar) radiation

solar radiation, hemispherical see hemispherical (solar) radiation

solar (thermal) collector a device designed to absorb solar radiation and to transfer the thermal energy so produced to a fluid passing through it. Note: the use of the term ‘panel’ is deprecated to avoid potential confusion with photovoltaic panels (ISO 9488:1999)

space heating system a heating system providing heat to maintain thermal comfort in a building; in French, installation de chauffage des locaux or chauffage; in German, Heizungsanlage, Heizung or Raumheizungsanlage stagnation status of a collector or system when no heat is removed by a heat transfer fluid (ISO 9488:1999)

storage, heat see heat storage store, heat see heat store

stratifier a device for enhancing stratification in the heat store. See Section for details. Synonym of‘stratifying unit’ stratifying unit see stratifier system, drainback see drainback system system, forced-circulation see forced-circulation system system, heating see heating system system, reference see reference system system, solar heating see solar heating system

system, solar-plus-supplementary see solar-plus-supplementary system

system, space heating see space heating system

system, thermosiphon see thermosiphon system

technology, ‘low-flow’ see low-flow technology

temperature, flow see flow temperature

temperature, return see return temperature

thermal collector, solar see solar (thermal) collector

thermosiphon system a solar heating system that utilizes only density changes of the heat transfer fluid to achieve circulation between collector and storage device or collector and heat exchanger (ISO 9488:1999)

total energy consumption, combined see combined total energy consumption

useful energy the energy drawn by consumers from their own appliances after its final conversion (i. e. in its final utilization) (Energy Dictionary, 1992). Note: light, mechanical energy and comfort heat are examples of useful energy


[1] Room temperature: The controls on the heating system were set in such a way that the room temperature is kept around fR = 20 ± 0.5°C and never drops below 19.5°C during heating season. For buildings with a floor heating system that use the thermal mass of the floor as a heat storage, the room temperature was allowed to range between 19.5 and 24°C. Temperatures above 24°C were excluded from the analysis because solar combisystems for heating purposes and not the buildings (with their specific overheating characteristic) were to be compared.

• Ventilation: The air change rate of ventilation is assumed to be 0.4 Ir1 based on the gross volume of the building. This rate is assumed in most European standards. No air heat recovery system was used.

• Shading: There was no internal or external shading device used, because only the heating period was analysed and shading is mainly used at times when overheating occurs and no space heating is needed.

[2] Due to the discretization of flow rates of 0.11/min, only multiple values of 0.6 1 are possible for the yearly volume.

f The maximum energy of one draw-ofF is 23.9 litres/minute x 1 kg/litre x 6 minutes x 1.16Wh/(kgK) x 35 К = 5822 Wh (the suggested maximum heat demand according to DIN 4708 (1994) is Q = 5820 Wh, => Vm„= 23.9 litres/minute).

* In periods when the solar collectors are able to cover by themselves the whole space heating demand, the water for space heating, after being heated up by solar energy flows through the turned-off auxiliary boiler. However, in some systems it is possible to bypass the auxiliary heating device by means of manually operated valves

The classification code of a solar combisystem includes one letter for Feature 1 and a second letter for Feature 2. In addition, there are three optional features indicated by lower­case symbols after the main code, if relevant for the generic system under consideration:

• d indicates that the solar combisystem is a drainback system, i. e. a solar thermal system in which, as part of the normal working cycle, the heat transfer fluid is drained from the solar collectors into a storage device when the pump is turned off, and refills the collector when the pump is turned on again.

[4] і indicates that there is a gas or oil burner integrated into and sold with the storage device. The і indicator always implies the mixed mode as the auxiliary heat management category (M as second main code letter).

• l indicates that the combisystem may be used with an auxiliary energy source like wood in the form of /ogs, which require a long running time for the auxiliary boiler at more or less fixed power. A long-running-time auxiliary

[5] it acts as a flat-plate collector

• it improves the building’s thermal insulation

• it provides weather protection

• it acts as a structural design element for the facade.

[6] All use the same reference collector, defined in section 6.1.2. This was necessary for system concepts, including hydraulic design and control strategies, to be compared. The results cannot be used directly for intercomparison of commercial systems, because the solar collectors in commercial systems have different characteristics from those of the Task 26 collector.

• The boiler is part of the system and thus varies from system to system, as do the store losses (see Table 6.13)

[7] Values are given for the space heating storage tank. Auxiliary energy for domestic hot water is brought in a separate small tank (80 litres), with a heat loss rate of 1 W/K and a set-point temperature of 47.5°C

[8] For all systems except System #3a,/av ext is lower than f^y therm by approximately 2% for small FSC values and 7-10% for larger FSC values. This means that System #3a uses less parasitic electricity than others, especially when the collector area increases.

• Systems #3a and #15 are close together, with System #15 better at low FSC values and System #3a better for large FSC values.

[9] Even if representative points are rather scattered, a general decrease of both the total and the additional specific costs can be observed when the collector area increases.

[10] As far as possible the system should be pre-assembled in the factory by the manufacturer’s skilled staff. More and more manufacturers of combisystems are following this trend, which started more than a decade ago in the solar water heater market. Factory assembly is at the same time a cost reduction factor.

• The design should strive for a high level of system integration, e. g. boiler, heat exchangers and stratifiers integrated in the tank. Generic Systems #8 and #15 are good examples of this approach.

• A number of‘hardware’ measures should be taken to prevent possible wrong installation: flow and return lines can be of different diameters or colours; three-way valves should be clearly marked; groups of hydraulic components (e. g. pump, valves, check valve, fill-in and drain valves in the collector loop, as

[11] the boiler efficiency

• the temperature of the auxiliary heated part of the store (thermostat setting for store charge)

• the volume heated by the auxiliary heater.

[12] There should always be enough hot water in the store to fulfill the heat demands. The peak heat demand in single – or double-family houses occurs when a bath tub is filled (about 25 kW). Therefore, the recommended volume for the DHW can be calculated from this demand and the power of the auxiliary heater. Additionally it must be possible to deliver heat from the auxiliary heater to the space heating system as well. Therefore, the outlet position must be below the DHW and the space heating outlet.

• The auxiliary heater often needs a minimum running time (especially solid wood burners).The volume between auxiliary heater inlet and outlet must be sufficient to prevent overheating during this minimum running time.

[13] a system

• a climate

• a collector area

• a reference consumption.

[14] The passive gains on the south face are optimized thanks to a large window area, with low-emissivity glass.

• Protection against the wind on the north side of the building is provided by small windows and service rooms (shed, boiler room).

• The wall construction consisting of a wooden frame with an insulation thickness of 15 cm reduces the thermal losses.

[15] 100 mm wall insulation

• 200 mm roof insulation

• prefabricated concrete block walls.