**Table 3.**

*Building characteristics.*

the thermal insulation are density = 16 kg/m3 , thickness = 0.05 m, and thermal conductivity = 0.05 W/m K.

The air conditioning systems used are available in the TRNSYS standard library. This catalog-based component with its own external file predicts the performance of the chiller based on the available range of input data [7]. The file provides values of normalized capacity and COP values as a function of inlet hot water, inlet cooling water, and inlet chilled water temperature.

The absorption (Type107) uses a catalog data lookup approach to predict the performance of a single-effect, hot water-fired absorption chiller. In this design, the heat required to desorb the refrigerant is provided by a stream of hot water. The cooling water stream absorbs the energy dissipated by the absorber and condenser components, and the machine is designed to chill a third fluid stream to a user designated set point temperature. The rated capacity specified was 37,800 kJ/h and a COP rated of 0.70. A thermal fluid was used with a 2.13 kJ/kg °C.

The adsorption chillers (Type 909) cool a liquid stream by evaporating water onto the surface of a solid desiccant matrix. The rated capacity specified was 37,800 kJ/h and a COP rated of 0.53. A thermal fluid was used with a 2.13 kJ/kg °C.

Similar equations are used for both cooling systems. The chilled water, the hot water, and the rejected energy are calculated with Eqs. (2)–(4):

$$\mathbf{m}\_{\text{CHW}} \,\mathbf{C} \mathbf{p}\_{\text{CHW}} \left(\mathbf{T}\_{\text{CW,IN}} - \mathbf{T}\_{\text{CHW,SET}}\right) = \text{MIN} \{\mathbf{Q}\_{\text{CHW}}, \mathbf{Q}\_{\text{CAPACITY}}\} \tag{2}$$

The energy of hot water.

$$\mathbf{Q\_{HW}} = \mathbf{m\_{HW}} \, \mathbf{C\_{PHW}} \left( \mathbf{T\_{HW,IN}} - \mathbf{T\_{HW,OUT}} \right) \tag{3}$$

The energy rejected (QCW) to the cooling water stream.

$$\mathbf{Q}\_{\rm CW} = \mathbf{Q}\_{\rm CHF} + \mathbf{Q}\_{\rm HW} + \mathbf{Q}\_{\rm AUX} \tag{4}$$

where QHW and QAUX are the energy of the hot water and the auxiliary equipment (pumps). TCW,IN and TCHW,SET are the temperature of the input cooling water and the set point of the chiller.

The heater system (Type 6) is used to increase the temperature until the minimum generator temperature of the CC. It was considered to have an efficiency of 100%:

$$\mathbf{Q\_{HEATER}} = \mathbf{m} \, \mathbf{Cp} \, \left( \mathbf{T\_{OUT}} - \mathbf{T\_{IN}} \right) \tag{5}$$

**93**

sponding to **Figure 5**.

*Thermal Analysis of an Absorption and Adsorption Cooling Chillers Using a Modulating…*

*hAIR*(*TAIR*,*OUT*,*DESIGN*) = *hAIR*(*TAIR*,*IN*,*DESIGN*) + \_\_\_\_\_\_\_\_\_\_\_

to provide the effectiveness of the heat exchanger and inlet conditions:

where QMAX is the maximum heat transfer rate across the exchanger. The pumps compute a mass flow rate using a variable control function (0 ≤ γ ≤ 1) and a fixed (user-specified) maximum flow capacity (mMAX).

Type 510 models a closed circuit cooling tower; a device used to cool a liquid stream by evaporating water from the outside of coils containing the working fluid.

QDESIGN = mWATER CpWATER (TIN,DESIGN –TOUT,DESIGN) (6)

The heat exchanger (Type 91) relies on an effectiveness (ε) minimum capacitance approach to model a heat exchanger. Under this assumption, the user is asked

QHX = ε Qmax (8)

mIN Cp (TOUT − TIN) = P<sup>∗</sup> fpar (9)

mOUT = γ mMAX (10)

where fpar is the fraction pump power, p is the power (kW), mOUT is the output mass flow rate (kg/s), and Cp is the heat capacity of the fluid (kJ/kg°C). **Table 4**

The differential controller (Type 2b) is an on/off differential controller that can have a value of 1 or 0. The value of the control signal is chosen as a function of the difference between the upper (THIGH) and lower (TLOW) temperatures, and both are compared with two dead-band temperature differences ΔTHIGH and ΔTLOW. The new value of the control function depends on the value of the input control func-

The mass and energy balances of the MTV (type 62) are calculated using equa-

m1 = m5 (11)

m3 = m4 (12)

m1 h1 = m2 h2 + m3 h3 (13)

m5 h5 = m2 h2 + m4 h4 (14)

where h is the specific enthalpy and m is the flow rate and subscripts corre-

The cooling thermostat (Type 1503) is an N-stage cooling aquastat/simple thermostat modeled to output on/off control functions that can be used to control a fluid cooling system having up to an N-stage heating source. The desired fluid temperature may depend on the time of day or the day of the week. These variations of the cooling set point temperatures are modeled using an optional setup control

*QWATER*,*DESIGN*

*mAIR* (7)

*DOI: http://dx.doi.org/10.5772/intechopen.84737*

shows the input data supplied to the pumps.

function and a setup temperature difference [4].

tion at the previous time step.

tions from 11 to 14, respectively:

*Thermal Analysis of an Absorption and Adsorption Cooling Chillers Using a Modulating… DOI: http://dx.doi.org/10.5772/intechopen.84737*

Type 510 models a closed circuit cooling tower; a device used to cool a liquid stream by evaporating water from the outside of coils containing the working fluid.

$$\mathbf{Q\_{DESIGN}} = \mathbf{m\_{WATER}} \mathbf{C\_{WATER}} \left( \mathbf{T\_{IN,DESIGN}} - \mathbf{T\_{OUT,DESIGN}} \right) \tag{6}$$

$$h\_{\rm AIR} \left( T\_{\rm AIR,OUT,DESION} \right) = h\_{\rm AIR} \left( T\_{\rm AIR,IN,DESION} \right) + \frac{Q\_{\rm WATER,DESION}}{\overline{m\_{\rm AIR}}} \tag{7}$$

The heat exchanger (Type 91) relies on an effectiveness (ε) minimum capacitance approach to model a heat exchanger. Under this assumption, the user is asked to provide the effectiveness of the heat exchanger and inlet conditions:

$$\mathbf{QHX = e \ Qmax} \tag{8}$$

where QMAX is the maximum heat transfer rate across the exchanger. The pumps compute a mass flow rate using a variable control function (0 ≤ γ ≤ 1) and a fixed (user-specified) maximum flow capacity (mMAX).

$$\mathbf{m}\_{\rm IN} \, \mathbf{C} \mathbf{p} \left( \mathbf{T}\_{\rm OUT} - \mathbf{T}\_{\rm IN} \right) = \mathbf{P}^\* \mathbf{f} \mathbf{p} \mathbf{r} \tag{9}$$

$$\mathbf{m}\_{\text{OUT}} = \mathbf{\color{red}{\mathbf{y}}} \mathbf{m}\_{\text{MAX}} \tag{10}$$

where fpar is the fraction pump power, p is the power (kW), mOUT is the output mass flow rate (kg/s), and Cp is the heat capacity of the fluid (kJ/kg°C). **Table 4** shows the input data supplied to the pumps.

The cooling thermostat (Type 1503) is an N-stage cooling aquastat/simple thermostat modeled to output on/off control functions that can be used to control a fluid cooling system having up to an N-stage heating source. The desired fluid temperature may depend on the time of day or the day of the week. These variations of the cooling set point temperatures are modeled using an optional setup control function and a setup temperature difference [4].

The differential controller (Type 2b) is an on/off differential controller that can have a value of 1 or 0. The value of the control signal is chosen as a function of the difference between the upper (THIGH) and lower (TLOW) temperatures, and both are compared with two dead-band temperature differences ΔTHIGH and ΔTLOW. The new value of the control function depends on the value of the input control function at the previous time step.

The mass and energy balances of the MTV (type 62) are calculated using equations from 11 to 14, respectively:

$$\mathbf{m}\_1 = \mathbf{m}\_5 \tag{11}$$

$$\mathbf{m}\_{\mathfrak{J}} = \mathbf{m}\_{\mathfrak{A}} \tag{12}$$

$$\mathbf{m}\_1 \,\mathrm{h}\_1 = \mathbf{m}\_2 \,\mathrm{h}\_2 + \mathbf{m}\_3 \,\mathrm{h}\_3 \tag{13}$$

$$\mathbf{m}\_5 \,\mathbf{h}\_5 = \mathbf{m}\_2 \,\mathbf{h}\_2 + \mathbf{m}\_4 \,\mathbf{h}\_4 \tag{14}$$

where h is the specific enthalpy and m is the flow rate and subscripts corresponding to **Figure 5**.

*Zero and Net Zero Energy*

the thermal insulation are density = 16 kg/m3

water, and inlet chilled water temperature.

conductivity = 0.05 W/m K.

**Table 3.**

*Building characteristics.*

The energy of hot water.

and the set point of the chiller.

, thickness = 0.05 m, and thermal

The air conditioning systems used are available in the TRNSYS standard library. This catalog-based component with its own external file predicts the performance of the chiller based on the available range of input data [7]. The file provides values of normalized capacity and COP values as a function of inlet hot water, inlet cooling

**Concept Quantity** North and south wall, m2 35 Ceiling and floor, m2 75 West and east wall, m2 12.5 Thickness of walls (brick), m 0.12 Thickness of insulating (polyurethane), m 0.05 Windows, m2 2 Air change of ventilation, h<sup>−</sup><sup>1</sup> 6

The absorption (Type107) uses a catalog data lookup approach to predict the performance of a single-effect, hot water-fired absorption chiller. In this design, the heat required to desorb the refrigerant is provided by a stream of hot water. The cooling water stream absorbs the energy dissipated by the absorber and condenser components, and the machine is designed to chill a third fluid stream to a user designated set point temperature. The rated capacity specified was 37,800 kJ/h and

The adsorption chillers (Type 909) cool a liquid stream by evaporating water onto the surface of a solid desiccant matrix. The rated capacity specified was 37,800

Similar equations are used for both cooling systems. The chilled water, the hot

mCHW CpCHW (TCW,IN –TCHW,SET) = MIN(QCHW,QCAPACITY) (2)

QHW = mHW CpHW (THW,IN –THW,OUT) (3)

QCW = QCHW + QHW + QAUX (4)

where QHW and QAUX are the energy of the hot water and the auxiliary equipment (pumps). TCW,IN and TCHW,SET are the temperature of the input cooling water

The heater system (Type 6) is used to increase the temperature until the minimum generator temperature of the CC. It was considered to have an efficiency of

QHEATER = m Cp (TOUT –TIN) (5)

kJ/h and a COP rated of 0.53. A thermal fluid was used with a 2.13 kJ/kg °C.

a COP rated of 0.70. A thermal fluid was used with a 2.13 kJ/kg °C.

water, and the rejected energy are calculated with Eqs. (2)–(4):

The energy rejected (QCW) to the cooling water stream.

**92**

100%:


**Table 4.**

*Parameter supplied to the pumps of the cooling system.*

#### **3.3 Parameters**

The energetic performance of the cooling systems can be evaluated using two indicators: solar fraction (SF) and heating fraction (HF). Solar and heating fractions are defined as the amount of energy supplied by solar resources (QCOL) and heater system (QHEATER), respectively, divided by the total energy supplied (QCOL + QHEATER).
