Category EuroSun2008-7

Description of installed system

1.1. System and operation concept

The system concept is shown in Fig. 1. The core components are the reversible adsorption machine which can be operated as a thermally driven chiller or heat pump and the borehole system that is used as heat rejection system for the chiller mode as well as the low temperature heat source for the heat pump mode.

In the summer operation mode (left schematic in Fig. 1) the adsorption machines works as a thermally driven chiller. It is driven by the heat from the solar collectors. A connection to the heating network of the building works as a heat backup in case of not sufficient solar driving heat. The system provides cooling to a cooling coil in the air handling unit, which is installed in the inlet air duct to the institutes’ canteen kitchen (3000m3/h)...

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The basic absorption model

Fig. 2 represents the thermodynamic states of the ideal simple effect absorption cycle, assuming mechanical, thermal and chemical equilibrium and assuming energy degradation exclusively concentrated on expansion valves. Steady state mass and energy balance in components yield the following equations:

Evaporator (no superheating):

Qm= m ref, K – h1); h1 = К

(2)

m ref, i X strong X weak

Considering =

(3)

weak strong

strong x weak

 

(4)

 

strong

 

2v

 

GENERATOR

 

CONDENSER

 

image641image642

image371

(a) (b)

Fig. 2. (a) LiBr/water absorption cycle. (b) Diagram P(T)-T LiBr/water

Generator (no superheating):

Mass balance:

Energy balance:

Qoi = ™strong • h2s – mweak * К + ™^ ,г * h2v ; T2s = T2v

Подпись: (5)

image643 Подпись: (6) (7) (8)

™...

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Monitoring equipment and evaluation of raw data

The data acquisition system consists of internally integrating heat meters with matched Pt100 type temperature sensors. The integrator has a sampling rate of 1s and calculates cumulated energy amounts and mean temperatures and powers. This internal sampling rate assures a correct collection of energy data for the highly dynamic temperature patterns characteristic of adsorption systems. The integrator and further temperature sensors are read out by a computer with a sampling rate of 15s. The monitoring software further reduces these values to cumulated energies and mean temperatures which are stored with an interval of 5 minutes in the raw data measurement file. The storage interval can be set by the system operator and thus allows a flexible data management...

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Experimental performance parameters

Experimental cooling capacity and COP is obtained from the external fluid temperatures in evaporators as follows:

 

QE, exp mchw Cw (tchw, in Phw, o )

From external fluid temperatures in generator:

QG, exp moil Coil (toil, in ^ oil, o )

Corresponding values per unit mass flow rate are:

Qe, exp

 

(16)

 

(17)

  image651

(18)

  image652

(19)

  image653

(20)

 

5. Results

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Overview of operation period

The results presented here correspond to the operation period from June 4th, 2007 to December 1st, 2007. From these 180 days the system was in operation during 108 day. The days without operation were either weekends or days without monitoring data due to a lightning stroke into the data acquisition system. Within these 108 days 1034 hours of operation were registered. In some hours the machine was in operation only a few minutes, but in most of the registered hours a

continuous operation was observed. In Table 1 the number of hours with an operation time within given limits is shown.

Operation

mode

Number of hours with an operation time t (in minutes) within the given limits

<15 min

15<t<30 min

30<t<45min

45<t<60 min

60min

cooling

65

23

36

37

282

heatin...

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Basic absorption model vs. experimental results. Factors affecting the facility performance

Подпись: to [°C] Fig. 3. Comparison of basic model and experimental results. (a) Ideal and experimental cooling capacity vs. tG (b) Ideal and. experimental COP vs. tG image655

Fig. 3 illustrates the comparison of experimental performance parameters with those obtained through the basic model, Eqs. (14) and (15), for 220 test points. The differences observed help identifying the influence of components performance, serving as a diagnosis. In the following, the causes of deviation from the ideal conditions are explained, evaluated and included in the model.

5.1. Influence of components performance. Modified basic model.

The evaporators in this facility layout show low performance [8]. Because of this, part of m ref

supplied to them is not evaporated, but overflows...

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Operation of the adsorption chiller

Performance of the chiller

In order to evaluate the performance of the chiller a comparison of experimentally measured cooling capacities and COPs with expected values from calculations is shown in Fig. 2. The experimental values were selected according to the following criteria:

1. a continuous operation during the whole hour as well as in the hour before and after,

2. stable temperatures with a small standard deviation has been measures in all three circuits,

3. only cooling operation was considered.

TCooling operation

For the evaluation of the cooling operation only hours with constant and steady operation were considered. Operation periods less than 60 minutes within one hour were not considered in this evaluation in order to avoid effects of transient states...

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FIRST RESULTS OF A SOLAR-THERMAL LIQUID-. DESICCANT AIR CONDITIONING CONCEPT

B. M. Jones* and S. J. Harrison

Department of Mechanical and Materials Engineering, Queen’s University, K7L 3N6, Kingston, Canada

* Corresponding Author, jones@me. queensu. ca

Abstract

A thermal low-flow liquid-desiccant air handling machine was procured, installed, and field tested. The goal of the present investigation is to evaluate the field performance of the machine and characterize its operation for the temperature range of a solar thermal array. The system studied includes a natural gas boiler supplying the heat, and a cooling tower for heat rejection. System performance was evaluated for the 50 to 90°C temperature range, the operating range of solar thermal collectors. Cooling power varied between 4.3 kW and 22...

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