First a test prototype of the chiller with a cooling capacity of about 10 kW was built and tested under laboratory conditions. For the second prototype some improvements were done and the cooling capacity was raised to 15 kW.

Figure 3: Cooling capacity for different cold water temperatures

The cooling capacity and the coefficient of performance (COP) of the second prototype for different cold water temperatures are shown in Figure 3 and Figure 4.

The figures show a distinct dependency on the cold water temperature. The higher the cold water temperature the higher is the cooling capacity and the coefficient of perform­ance of the chiller. In this capacity range the chiller will mostly be used for cooling only but not for air-dehumidification. By considering the cold water temperature when designing the room cooling system a high COP and cooling capacity can be achieved.

Figure 4: Coefficient of performance for different cold water temperatures

Field test

After prototype testing under laboratory conditions a field test was carried out in the sum­mer of 2003. At three test sites the new absorption chiller was installed. The locations of the test sites and the different peripheral equipment that was used is specified in Table 2.

The field test showed good results. The absorption chiller worked with a high reliability and operational safety. It is able to work over a wide range of external conditions. The test in Italy showed that the chiller even works with flat plate collectors (lower heating tempera­tures achievable than with vacuum tube collectors) and a dry cooler for re-cooling (rela­tively high cooling water temperatures during daytime).

At the test site in Kothen the room cooling system (gravity cooling units without ventilation) was already installed. It is designed for lower cold water temperatures and could not be changed for this field test. Therefore the absorption chiller had to work with cold water temperatures of 10…12 °C. Also the hot and cold water flow rates were below design con­ditions. Because of these conditions the absorption chiller reached a lower COP as shown before.

Results of the chiller operation in Kothen for one summer day are shown in Figure 5 and Figure 6. On this day some variations of the solution flow rate and the desorber heating temperature were carried out.

The tests also showed that a precise adjustment of the two solution flow rates is very im­portant for achieving a high COP. If one solution pump is pumping more solution than the other one solution reservoir will frequently be empty. This results in a short stop (some seconds) of the operation of the pump. During this stop the solution heat exchanger is without effect which affects the whole cycle of the absorption chiller. The chiller needs minutes to recover and to reach the former values of operation (COP and cooling perform­ance).

Location latitude	Heat source	Recooling	Cold water use
Neumarkt, Italy	46,4° (N)	flat plate solar thermal collectors, 55 m2	dry cooler (fan coil)	room cooling with fan coils
Westenfeld, Germany	50,4° (N)	waste heat of an engine driven cogeneration unit	dry cooler (fan coil)	room cooling with fan coils
Kothen, Germany	51,7° (N)	CPC-vacuum tube collec­tors^ m2	wet open cool­ing tower	cooling of office space; gravity cool­ing system

Table 2: Test sites — location and equipment

The experiences of the field test lead to some further improvements of the chiller design to increase the COP and the flexibility. The electrical power consumption of the peripheral equipment (pumps) could be reduced.

The chiller that is shown in Figure 7 was presented at the IKK fair in Hannover in October 2003. Additional field testing and the composition of "standard” solar thermal cooling con­figurations using the small capacity absorption chiller are planned for the next cooling sea­son.

-□— temp. hot water in — — A — temp. cold water out Time — О — temp. hot water out — O— temp. cooling water in — V temp. cold water in temp. cooling water out

——- condensation pressure • • • • evaporation pressure

Figure 5: Results of the field test in Kothen — temperatures and pressures (8.8.2003)

7500 7000 6500 6000 5500 4| 5000 4500 4000 3500 3000 2500 2000 1500 1000 500

ra CL <D

CL

Another focal point will be the coupling of the absorption chiller with other heat sources for example waste heat of thermal biomass usage or cogeneration units.

SHAPE * MERGEFORMAT

—о— Heating capacity [kW] jjme cop — О — Cooling capacity [kW]

COP

Figure 7: Small capacity H2O/LiBr absorption chiller Wegracal SE 15

Figure 6: Results of the field test in Kothen — capacities and coefficient of performance (8.8.2003)