1.2. Introduction

Sizing of component is done for one floor. Extrapolation can be done to the whole building. For the different locations, the device power is equal to the maximum heating and cooling load computed before. Nevertheless the same performances are chosen whatever the nominal power. The three cases differ only by the heating and cooling production plant. Emission and distribution of heat/cold is kept as described above. In this way decoupling can be done about two parts of the simulation: building consumption; heating/cooling system consumption. For cases where solar energy is used, the collectors field is assumed to be located on the roof. This implies a limitation of collectors area. To go through this limitation, two versions are presented for case 2 and 3: one roof for 12 floors (case B.), one roof for 3 floors (case A).

1.3. Case 1: Gas boiler and vapour compression chiller

Heating and cooling production for this case has also been defined in the frame of the IEA Annex 48 report. Gas boiler performance is the same for each case: yield at 100 % load is 89.2 %; yield at 30% load is 88.2 %; losses at 0% load are 1.3 kW. Interpolation is done between these points. Heating curve has set point between 45°C and 90°C depending on external temperature.

The cold production is provided by an air-chiller with COP = 3.5. The set point of cold water is always 7°C whatever the case and external conditions. Due to lack of data, part load performance decrease is not taken into account.

1.4. Case 2: Gas boiler, vapour compression chiller, PV field

Gas boiler and chiller have similar behaviour as for case 1. The only difference is that Photovoltaic panels are placed on the roof to feed electrical grid (Panel chosen: SHARP NDL3E62). Given the roof surface, optimisation is done to produce maximum electricity on a yearly basis. A special TRNSYS shading model dedicated to PV is implemented (Type 551). A location has an optimal inclination angle

[5] , the optimal number of rows is found (10 rows). Inverter efficiency is set to 0.78. It is assumed that PV panels work at their optimal point (current-voltage) each time. For case 2A building has 3 floors for case 2B, 12 floors. Roof panel field contains 700 elements and has a total net area of 610 m2.

1.5. Case 3: Gas boiler, solar thermal field, absorption chiller

For this case, gas boiler power is designed to feed the absorption chiller when the load is maximum. It implies a higher power value than for previous cases. The heating/cooling system of case 3 requires additional equipment:

• Solar thermal panels : evacuated tube collector SCHOTT ETC 16

• Absorption chiller : YAZAKI WFC-SH 30 (Nominal point : 105 kWcold; thermal COP = 0.695)

• Storage tank

• Cooling tower : AEC Cooling Tower Systems FG 2004

• Heat exchanger

The central element of the simulation scheme is the storage tank (TRNSYS type 534); four circuits are linked to it: gas boiler, building heating network, absorption chiller hot water circuit and solar panel circuit. 20 cm width rockwool insulation has been modelled in order to decrease storage losses.

Storage tank volume is optimized: this value ranges from 3 to 11 m3 depending on the simulation case and location.

Absorption chiller behaviour has been implemented in a new TRNSYS type 255 (nearly the same as existing type 107) based on manufacturer curves [6] . The model takes into account the energy balance, but not the chiller inertia nor other dynamic effects. Cooling tower fan speed is controlled by rejection circuit temperature. Solar energy passes trough a heat exchanger (95% efficiency) and heats the bottom of the storage tank. Its upper part is heated at 89°C by gas boiler in order to feed the absorption chiller at nominal point. No temperature control neither flow variation is provided on the hot water. Nominal power for absorption chiller is 105 kW for Paris and Stockholm, 150 kW for Lisbon.

The whole solar field has a net collector area of 427 m2 and the slope is optimized for each location. There are four rows (less than case 2 due to size of panels). Mass flow of the fluid has been chosen to 30 litres/(m2_coll_net_area hour) [7] . New auxiliaries’ consumptions have to be taken into account in this case. Common values are given by H.-M. Henning [8] : 0.02 kWhelec/kWhth for solar system, 0.03 kWhelec/kWhth for heat rejection, 0.01 kWhelec/kWhth for absorption chiller.

2. Results

2.1. Introduction

Hereafter are presented simulations results for each case and each location. They emphasize the energy consumption of building. Variable selection for presentation is based on reference book [9]; for example, primary energy savings are related to collector area. When converting net energy consumption in primary energy consumption, the selected coefficient is 2.5 for electricity and 1 for fossil fuels. These are legal values for Belgium. All values are given in kWh by building squared meter per year (building area is 15000 m2 for twelve floor, internal zones area is used), or other units if necessary.