ir. A. B. Schaap, drs. M. J. de Bruijn, Ecofys, Kanaalweg 16-G 3526 KL Utrecht,

The Netherlands. A. Schaap@Ecofys. nl

The standard solar domestic hot water system (in the Netherlands around 3 m2 collector area and around 100 litre of storage capacity) is developing into a solar combi system with around 6 to 8 m2 of collector area and around 200 to 300 litre of storage volume. This combi system can deliver more than half of the hot water demand of an average single family house and a small part of the heating demand in winter. This system has a big surplus of energy in summer. This surplus can be used for air conditioning in combination with a sorption heat pump. In summer the solar system drives the sorption system to deliver cooling. In winter the sorption system is driven by the auxiliary burner as a heat pump to produce space heating. In this way a very high CO2 reduction can be accomplished, by using the sorption system as well as the solar system all year round. The feasibility of such a system was studied.

The natural gas boiler for space heating and hot water has reached its thermodynamic limit. The efficiency is near to 100 % of the higher heating value. The efficiency on domestic hot water is somewhat lower but this efficiency is rising rapidly.

The industry is searching for ways to overcome the 100 % barrier. There are several solutions for this challenge:

• An electrical compression heat pump.

• A combination of a natural gas boiler with a small electric heat pump.

• A natural gas (micro) combined heat and power system (internal combustion, Stirling or fuel cell)

• A natural gas driven sorption heat pump.

With these solutions the primary energy efficiency can be raised to 120 to 160 % of the higher heating value, by using the exergy of the combustion. All four solutions have their pros and cons and it is in this stage not clear which solution will dominate which part of the market. The general advantage of the sorption heat pump is that the operational costs are related to the costs of the heating fuel (natural gas, oil etc.) and hardly to the costs of electricity as the other three options are.

We are especially interested in a combination of the sorption heat pump with a solar thermal system. This can be accomplished in the following way. In summer the solar system drives the sorption system to deliver cooling (see figure 1). At the same time the solar system produces hot water with the gas boiler as auxiliary heater. The sorption system rejects heat to the ambient. In winter the sorption system is driven by the gas boiler as a heat pump to produce space heating. The sorption system extracts heat from the ambient. Hot water is produced by the solar system, by the sorption system and by the gas boiler. The solar system produces also a small part of the space heating demand. The cooling delivery system in summer can be the same system as the heating delivery system in winter. The heat rejection subsystem in summer can be the same system as the heat extraction subsystem in winter.

The aim of the study was to determine the feasibility of such a system. The market that we are aiming at is the cooling, heating and hot water demand of buildings. The buildings can be subdivided into single family houses and commercial and institutional buildings. We concentrated on the single family houses, because it is the largest market with the largest numbers of one single type of product.

The single family houses can be subdivided into existing and newly build houses and into:

• Detached houses (build apart from each other)

• Terraced houses (build in rows)

• Apartment buildings (in stacks of houses)

In the Netherlands there are about 6 million existing houses and every year about 70,000 houses are build. So with a replacement every 15 years on average, the replacement market is with approximately 400,000 units bigger than the market for newly build houses. Figures 2 and 3 give an overview of a solar sorption system in the summer and in the winter situation.

^ Y Ambient

We can see that a valve is needed to switch from summer operation (condenser delivers waste heat and evaporator delivers cooling) to the winter operation (condenser delivers heating and the evaporator extracts heat from the ambient). The heat delivery system can be the same system as the cold delivery system (for example floor/wall heating or air heating). The waste heat in summer and the source heat in winter can be delivered/extracted to/from the ambient air, or can be integrated with the ventilation system.

To be able to simulate the solar sorption system we need demand patterns of typical houses over a typical year. In The Netherlands newly build houses have to comply with an energy standard called the EPN (Energie Prestatie Normering). Of course it is allowed to build more energy efficient than the standard. In this way we came to two different typical newly build houses; a reference house build according to the energy standard and a minimum energy house in which the heating demand was reduced to the technical limits.

For the existing buildings we have also chosen two typical cases. The average house according to the Dutch national energy inquiry (BAK) and a big house with a double as high floor area, but the same construction. These four houses form a reasonable cross section of the Dutch single family housing market as a whole. The demand of existing apartment buildings will fit between the reference house and the average house. Newly build apartment buildings fit between the reference house and the minimum house.

With an Ecofys house simulation program we generated hourly values of the space heat demand for these four different single family houses.

Reference house: In 2003 newly built houses have to reach an EP (Energy Performance) value of 1.0 to obtain a building permit. The lower the EP the lower the heating demand (all other aspects equal). The NOVEm single family terraced reference house was chosen (1999 tuinkamer tussenwoning). The house is calculated with the EP calculation program and subsequently with an Ecofys house simulation program using the Test Reference Year for De Bilt to generate hourly values of the space heat demand. The house has a floor area of 111 m2 divided over two stories and an attic. It has a calculated heat demand for space heating of 10.8 GJ/year.

Minimum Energy house: This house has the same dimensions as the reference house. In this case however the heat loss of the house is reduced to the technical limits (thicker insulation and triple glazing). The calculated heat demand is only 5.8 GJ/year for space heating. In this calculation the internal heat production was lowered from 750 W (for the other three houses) to 400 W continuously, because we expect the people in such dwellings

to use energy efficient appliances. If not so the heating demand can even be as low as

1.5 GJ/year (comparable to a passive house).

Average house: This house is based on the heat demand for an average existing Dutch house (BAK 2001). The calculated space heat demand is 35 GJ/year.

Big house: This house has the same construction as the average house only the floor area is increased with a factor of two. This house was added because it can be expected that sorption systems will be first cost effective in houses with a high heat demand. The space heat demand is 64 GJ/year.