0378-7788/$ – see front matter © 2013 Elsevier B。V。 All rights reserved。 http://dx。doi。org/10。1016/j。enbuild。2013。09。001

B。 Prasartkaew, S。 Kumar / Energy and Buildings 68 (2014) 156–164 157

Chilled water for air conditioning

Fig。 1。   Conventional and proposed solar cooling system。

connected in series with the solar water heating system, (Case 2) an auxiliary heater is connected in parallel with solar collector, and (Case 3) an auxiliary heater is connected in parallel with the solar water heating system。

The common feature in all the three cases is that the insulated biomass gasifier boiler has two functions: it works as an auxiliary energy source when solar energy is not enough and works as the main heat source when the solar radiation is not available。 In Case 1 and 3, the gasifier boiler is controlled by a controller and sup- plies hot water to the generator of the absorption chiller。 The solar energy heats the water at the collector field which is then pumped to the hot water storage tank。 This pump will be activated by con- troller。 Usually, it remains off until the difference between collector outlet and inlet water temperature is above the upper dead band value。 The controller will switch the pump off when this difference reaches the lower dead band。

The cooling is provided by a single-effect LiBr–H2O absorption chiller。 Heat from solar collector or from biomass-boiler evaporates the water (strong solution of water and LiBr) in the generator of the absorption chiller。 This is led to the condenser, where it rejects heat to the ambient and condenses。 This is taken to the evaporator through the expansion valve, where it receives heat from the space to be cooled and evaporates。 The evaporated refrigerant (water) is absorbed by the weak solution in the absorber (from the genera- tor)。 The absorption process also releases heat to the ambient, and the solution, now rich in water (strong solution) is taken to the gen- erator (by a pump) to complete the cycle。 The heat required for its generator is drawn from hot water pumped from a hot water stor- age tank fed by the solar collectors and/or sometimes boosted/fed

by biomass boiler。 The condenser and absorber of absorption chiller are cooled by water pumped through a cooling tower。 The chilled water produced from evaporator is pumped for cooling proposes。

3。Mathematical model and input parameters used for the design

that the fossil auxiliary heat source is replaced by biomass based gasifier boiler。

Fig。 2 shows three possible system configurations for solar- biomass hybrid cooling system: (Case 1) an auxiliary heater is

The mathematical model of the SBAC system and its validation presented in [3] was used in the system configuration selection and system design。 The procedure used the governing equations for each sub system, and that the inputs and outputs between each sub-system were according to the configuration in Fig。 2。 The model equations were constructed using the following assumptions:

(1)The model considered the energy and mass balances at each component, and of the overall system。

(2)The system is considered to be at steady state。

(3)The specific heat and density of the working fluids are constant。

(4)The loss of the water vapor and moisture (at the hot water storage tank and solar collector vents) is not taken into account。

(5)There is no pressure loss and no heat loss/gain in the lines (pipes) connecting the system components。

(6)The fluid temperatures increasing due to the friction in plumb- ing and valves, blowers and pumps are negligible。

158 B。 Prasartkaew, S。 Kumar / Energy and Buildings 68 (2014) 156–164