Category EuroSun2008-10

Solar Combi + systems


Solar Combi+ systems use heat from solar thermal collectors to provide heating in winter, cooling and summer and domestic hot water all the year round. Fig. 1 sketches the main components, which make up a typical system: (i) the solar thermal collector to provide the heat might be backed up by another heat source, (ii) a storage tank can either be installed on the warm side, as drawn in the figure, on the cold side or on both, (iii) the domestic hot water tank might be included in the hot storage or be a separate tank, (iv) the sorption chiller is fed with hot water (70-100°C), (v) rejects heat at intermediate temperature (30-40°C) to a cooling tower (dry, wet) or another heat sink (as e. g...

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Monitoring Results of a Solar Thermal System for. Hot Water Production in an Apartment Building

Jose Cavaco*, Pedro Horta, Joao Farinha Mendes,

INETI, Department of Renewable Energies, Campus do Lumiar do INETI, 1649-038 Lisbon, Portugal

* Corresponding Author, iose. cavaco@ineti. pt


Prior to recent building regulations enforcement, the use of Solar Thermal Systems (STS) in residential buildings was dependent on the proactive role of building promoters, as is the case of EPUL (Public Company of Urbanism of Lisbon), which has studied along the last decade, after a joint work with INETI, the possibility of using solar energy in new apartment buildings.

Such a STS was installed in a new multi-storey building just before the new building
regulations, making the use of solar energy in residential buildings mandatory, was enforced.

At the present, INETI is monitoring the STS over a...

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Experimental Apparatus

A schematic diagram is shown in Figure 2, depicting the main components of the ISAHP test rig. Table 1 lists the instrumentation and monitoring equipment used in the experiment, whose part numbers correspond to the schematic diagram.

Table 1

List of instrumentation used





Pressure/Temperature transducer (0-100 psi, Senstronics LTD)



Pressure/Temperature transducer (0-500 psi, Senstronics LTD)

F – 1

Ultrasonic flow meter (Emerson)

F – 2

Positive displacement flow meter (Oval Engineering)


Watt meter (ISW8001, Powertek)


Thermocouple (24 Gauge T-type, Omega)

Подпись: Fig. 2. Schematic diagram of the ISAHP Experimental rig
The main components of the apparatus include: a nominal 1/3 HP single speed compressor, a thermostatic expansion valve, tw...

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. Cost of solar collector area

To investigate the influence of the collector costs on the cost/benefit ratio and the dimensioning of the system, the specific collector price was gradually reduced to 70% of the base case. Such a reduction could be realistic with improved materials and/or production processes. All other parameters match the base case. Figure 3 (a) shows that the less expensive collectors lead to higher primary energy saving, due primarily to an enlargement of the absolute collector area in the optimal system configuration. In opposition to the enlargement of collector area the storage device capacity almost stays constant within the examined range of collector costs, which means that the specific storage volume decreases...

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Case 1 feasibility

The feasibility and sensitivity analysis for Case 1 with pellets and oil as fuel are shown in fig 3. With today’s pellet prices a feasible payback period cannot be found during the plants estimated lifetime. With annual pellet price increases of between 5-10% the feasible payback periods start to come within


the range of the estimated lifetime. With today’s oil prices a feasible payback period can be found in Sweden but not in Finland, where an annual oil price increases of between 2-5% would be needed.

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System description. Solar collectors

Two solar glazed panels heat up the heat carrier fluid of the solar loop. The absorbing total surface of the two collectors is 4 m[10] [11]. They are facing south (azimuth angle 0°) and have 45° with the ground. Neither roof integration nor shadows are considered. Collector parameters are: optical coefficient B = 0.81, firs order thermal coefficient k1 = 3.61W/m2K and second order thermal coefficient k2 = 0.0045 W/m2K2 . Stagnation temperature is 215°C’.

2.2 Storage tank

A 300 liters tank is used to storage the solar energy (figure 1). At the bottom of the storage tank an integrated heat exchanger supplies solar energy recovered by the panels. This exchanger is installed inside a stratifier high as 90% of the tank...

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Addressed barriers and offered solutions

The most important barriers for a broad application of small scale combined solar heating and cooling systems – further on called Solar Combi+ – and the solutions proposed by the project to overcome them are as follows:

1. Combined solar heating and cooling needs specialised design in order to make the single components play together optimally. So far every single system is designed from scratch. This (i) leads to a financial effort, which is not feasible for small applications, as design costs become prohibitively high in relation to hardware costs and (ii) often might overstrain the solar thermal installer, who would in most cases be the provider of the system to the end-user...

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Description of the system

The STS consists of 32 solar collectors with unit aperture area of 1.86 m2. The solar field is divided into 8 groups of 4 collectors oriented both at 27° (4 groups) and -63° (4 groups) azimuths, given architectural and space constrains. The tilt angle is 35°, optimized for the building latitude.

The effect of the decoupled orientation from south was studied on a daily basis and found never to exceed a 12% penalty (regarding an optimal south facing orientation) in monthly average (value for December, the less favourable month, being for example 8% in March, 1.35% in April, 0.87% in May and 0.16% in June).

The feeding of the collector batteries facing east and west is independent, thus using two separate lines starting in the pumping group (located in the basement, -1 floor).

After passin...

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