a)An auxiliary heater is connected in series with the solar water heating system (Case 1)

b)An auxiliary heater is connected in parallel with the solar collector (Case 2)

Motorized 3-way valve

c)An auxiliary heater is connected in parallel with the solar water heating system (Case 3)

Fig。 2。   Three possible system configurations for supplying hot water to the absorption system。

(7)The energy considered are solar and biomass energy, while the power consumed by other equipment (e。g。 pumps, blower, fans and controllers) is excluded。

。 1  if Tst > Tset,

ˇ =

0  otherwise。

(7)

3。1。Solar water heating system

。 1  if Tc,o

μ =

> Tst,

(8)

The expression (Eq。 (1)) for collector efficiency given by the

Hottel–Whillier Bliss equation was used:

Q˙ u  = m˙ cp(Tc,o  − Tc,i) = yc Ac GT (1)

where,

FRUL (Tc,i − Ta)

0  otherwise。

Whenever the temperature of hot water supplied to the chiller machine is lower than set point temperature, the auxiliary heat (Q˙ aux) is needed and this required heat will be supplied by the biomass gasifier-boiler。 This required heat can be determined as

yc = FR (ı˛) −

T

(2)

follows:

Tc,i  = ˇTst  + (1 − ˇ)Ta (3)

Q˙ aux  = (1 − ˇ)m˙ geCp(Tset  − Tge,o) (9)

。      Q˙ u        。

Tc,o = ˇ

Tc,i  + 。m˙

c Cp。

(4)

3。2。Biomass  gasifier-boiler

The temperature distribution in the hot water storage tank is

obtained from the energy balance expressed as:

。 dTst 。

The gas-fired boiler is modeled as a heat exchanger, where heat is transferred between combustion products and water。 The tran-

(MCp)st dt

= μQ˙ u  − Q˙ tl  − (UA)st (Tst  − Ta) (5)

sient temperature of water inside the boiler can be determined by:

where,  the  extracted  heat  Q˙ tl   and  control  function  used  for  the

collector and load energy terms, are defined as:

Q˙ tl  = ˇm˙ geCp(Tst  − Tge,o) (6)

(MCp)b

。 dTb 。 dt

= Q˙ gw  − Q˙ bl  − (UA)weCp,a(Tb  − Ta) (10)

B。 Prasartkaew, S。 Kumar / Energy and Buildings 68 (2014) 156–164 159

where, the added heat into the water heater boiler Q˙ gw and its effec-

h = ˙A + Tsol˙B + ˙CT 2

(27)

tiveness relations for the heat exchangers between    combustion

gases to water can be calculated from:

Q˙ gw  = ϕεgw (Q˙ PG  − m˙ fluCp,fluTflu) (11) where,

where, all of above cofactors (A–E) can be calculated as shown in [3]。

At point 7, the refrigerant is in superheated state and its enthalpy, h7 can be determined from

。 1    if Q˙ aux  > 0,

ϕ =

(12)

hsh =

。 HSH2 − HSH1 。 T

100

+ HSH1

(28)