1.1. Solar combisystem modelling

The first step in the study consists in the creation of a reference model of a solar combisystem. The system is designed to provide energy for space heating and domestic hot water for a single-family house. It is installed in a low energy house and does not include any long-term Thermal Energy Storage System (TESS). This reference case has been programmed with the transient system simulation program TRNSYS [2]. This software is a complete and extensible simulation environment for the transient simulation of energy systems, including multi-zone buildings. Its modular structure allows the user to build his own systems, from simple domestic hot water systems to the design of

buildings and their equipments, including control strategies, occupant behaviour, alternative energy systems (wind, solar, photovoltaic, hydrogen systems), etc.

The model of the reference combisystem is divided in several sub-sections as depicted in Fig. 2 :

• the solar collector loop with an area of 20 m2 of evacuated tube collectors and counter flow heat exchanger

• the auxiliary heating loop, comprising an electric heater

• the domestic hot water (DHW) demand module, controlled by a load profile and set to provide 200 L of water at 45°C per day, which is the daily consumption of a five-person family

• the building representation section, which corresponds to a low energy single family house of 191 m2 with a bioclimatic architecture

• the space heating loop, modelled with a radiator

• the weather data processing module, which reads the weather data and calculates direct and diffuse radiation outputs for the surfaces of the building and solar collectors with various orientations and slopes.

Weather

Coldpipe (31)

Solar collector loop

Evacuated tubes (71)

Weather (109)

Pump II (803)

Low energy house (56a)

Counter flow HX (5 b)

Building

Water tank (340)

Diverter (lib)

A

Radiator (362)

How mixer (11 h)

Tempering valve (lib)

Auxiliary heating

Load profile (14b)

Aux pump (803) Aux coldpipe (31)

Evaluation

Space heating

DHW

Fig. 2. Reference solar combisystem layout

This figure is a simplified layout ; all the controllers and regulation devices are omitted.

All these sub-sections are connected with the central stratified hot water tank with a total volume of 2.45 m3. The supply temperature of hot water is set at 45°C, but the setpoint temperature is 60°C in the upper part of the tank. Four double inlet/outlet ports are included in the tank, corresponding to the collector loop, the auxiliary heating loop, the DHW loop and the space heating loop. Five temperature sensors give the values of monitoring temperatures for the control units of the system, such as the protection temperature of the solar collector (Fig. 3).

DP3 input (from the aux. heating)

DP4 input (from the space heating) DP5 input (from the DHW demand)

DPI input (from the collector)

0.15 0.05

DP5 output ^(to the DHW demand) ^ DP4 output (to the space heating) *DP3 output (to space heating)

DP1 output (to the collector)

T1 : collector control temperature T2 : not used T3 : water tank protection from high temperatures T4 et T5 : aux. heater control

Fig. 3. Hot water tank — Relative heights of double ports and temperature sensors 2.2. Heat demand of the house The simulations have been performed for two different locations in France, Paris and Marseille, in order to evaluate the influence of the climate on the heat demand and the achieved solar fraction. That is why the solar collector area is far over-sized in Marseille, which is located in the south of the country.

Fig. 4. Space heating demand of the modelled house

The building has a space heating demand of 37.2 kWh. m-2 in Paris and 15.4 kWh. m-2 in Marseille. If space heating and DHW preparation are both considered, the demand rise to 53.0 kWh. m-2 and 31.1 kWh. m-2 for Paris and Marseille respectively.