Category EuroSun2008-10

Experimental Procedure

To compare the dynamic operation of the ISAHP system with the steady-state computer model [4], a 6 hour test with varying glycol temperature was performed. Due to stratification, the temperature at the bottom of the tank remained constant throughout the test providing a constant input temperature for the condenser on the water side. A description of the experiments performed is given below.

1.2. Test Sequence

For the simulated solar day test, the heat out of the auxiliary heater was varied in a sinusoidal profile similar to that occurring on a clear sunny day. The following procedure was followed for the test:

• Prior to testing the storage tank was filled with water at mains temperature to ensure that the entire tank was at constant temperature.

• During this time the collector loop flu...

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Efficiency curve of solar collector

For investigating the effect of the thermal behaviour of the solar collector on the entire system the optimisation process was executed with five different collector efficiency curves representing typical collectors available on the market [4], see Table 2.

collector

П0

[-]

a1

[W/(m2K)]

a2

[W/(m2K2)]

I

0.825

3

0.013

II

0.815

3.25

0.014

base case (bc)

0.8

3.5

0.015

III

0.78

3.75

0.0175

IV

0.75

4

0.02

Table 2. Simulated flat-plate solar collectors

Подпись: AT [K] Fig. 4. Efficiency curves of the solar collectors.

Figure 3 (b) illustrates that the respective optimal system configurations move towards higher primary energy savings while the additional costs become smaller when improving the solar collector...

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Case 2 feasibility

The feasibility and sensitivity analysis for Case 2 with pellets and oil as fuel are shown in fig 4. It can be concluded that 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 be shorter than the estimated plant lifetime. With oil as fuel feasible payback periods shorter than the estimated plant lifetime can be found already with both countries’ current prices.

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Heat lost to environment

The total thermal resistance of the vertical wall of the tank is:

image216

(1)

 

image217

Подпись: is obtained from the Nusselt number:The convection coefficient in air hair

Nuair = 0 if Ra < 104

Nuair = 0.59 ■ Rar0f if 104 < Ra < 109

Nuair = 0.13 ■ Ra033 elsewhere

The convection coefficient in water hwater is obtained from the next relationship:

image219 image220

г -|2

Supplementary losses appear for the first and the last element, at the top and the bottom of the tank. Different relationships are employed for these two horizontal surfaces in contact with ambient air depending on the temperature gradient. If heat is recuperated from the environment next correlations are computed:

Nuair = 0 if Ra < 104

Nuair = 0.54 • Ra0 25 if 104 < Ra < 109 (4)

Nuair = 0.54 • Ra0 33 elsewhere

And, if heat is lost to the environment, the correlations...

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Solar Combi + work plan

3.1. Market analysis

The market analysis provides an in depth analysis of markets for small scale SolarCombi+ and serves as a basis for the definition of the cases to be studied in WP3. It is performed on three pillars: (i) small scale chillers, (ii) solar thermal applications and (iii) consumers. The ecologically and economically rated case studies of WP3 are on the other hand the basis for a SWOT analysis, the examination of market shares and definition of goals.

3.2. Virtual case studies

Based on the results of the market analysis and on the experience with installed systems up to now, promising configurations will be identified, simulated for different typical conditions (i. e. utiliza­tion, climate, building type) and finally economically and ecologically rated.

WP1: Management ...

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Monitoring Scheme

The data collection system receives and stores all the information generated by the temperature differential controller (RESOL, DeltaSOL ES in multiple collector orientation with multiple heat delivery points operation mode) that in turn receives this information from the temperature probes and the flow meter on the totalizing line.

This information is available and can be downloaded locally, through ports and standard communications protocols, but also remotely, via a remote communication system (GSM modem), after connection to a Data logger (RESOL DL1), which can transmit via GSM through a SIEMENS TC35i modem connected to a YAGI ASPJ 810 antenna. The data download is done by using the data logger’s specific software: RESOL Service Centre.

The data downloaded from the data logger which ...

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Performance Parameters

The COP of the heat pump was determined by:

COP = Q^ (1)

W

comp

where Wcomp is the true power input to the compressor measured directly by the wattmeter, and Qc was determined by:

Qc = mr (h2- h) (2)

Where mr is the mass flow rate of the refrigerant, and h2 and h3 are the enthalpies at the inlet and outlet of the condenser, on the refrigerant side. Enthalpy is a function of both pressure and temperature, which are measured at each point throughout the cycle.

The natural convection flow rate, mNC can be determined by performing an energy balance across the condenser. Assuming the heat lost to the environment is negligible, as the condenser was well insulated, the energy balance is expressed as:

Qc = mr (h2 – h3) = mNCCp (T8 – T7 ) (3)

image183 Подпись: (4)

where Cp is the specific heat of the water...

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Insulation of the storage tank

The typical thickness of a PUR storage insulation is in the range of 10 to 12 cm [5]. Within this study the thickness has been varied between 7.5 cm and 17.5 cm (base case 15 cm). The results of the optimisation process for these variations are shown in Figure 3 (d) and Table 1.

The optimisation with 7.5 cm of insulation leads to a system with a storage device capacity of 0.77 m3 and a solar collector area of 12 m2. Thicker storage insulation leads to an improvement of the thermal behaviour of the system. Therefore with the same dimensioning and investment cost but thicker insulation a dot in Figure 3 would shift towards higher primary energy savings and simultaneously towards smaller additional costs (due to a reduction of running costs)...

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