Methodology

First, a residence is selected for modeling, and the overall heat transfer coefficient is calculated according to chosen residence's general construction elements given in Table 7.2. Then, using degree-hours values, cooling load of the residence is determined. Degree-hours values were also calculated by using data taken from Turkish meteorological data station for 23 years. Degree-hours values are calculated for three conditions: the warmest year, the coldest year, and the average values for 23 years, using hourly average temperatures. Degree-hours values are calculated for three conditions to realize how to change its range for best and worst conditions.

Table 7.2 Calculation of cooling load for an hour.

Outdoor temperature and relative humidity Indoor temperature and relative humidity Floor dimensions / volume of floor Infiltration Person

Lighting and electrical equipment_

10mx10mx3m/ 300 m3 4.5 times for 24 hours 4 persons (staying 16 hours) Works 16 hours

Area

U

AT

Heat gain

(m2)

(W/m2 °C)

(°C)

(W)

North

24

0.52

10

124.8

Outside wall

South (+2%)

24

0.52

10

127.3

East (+3%)

24

0.52

10

128.5

West (+3%)

24

0.52

10

128.5

Windows

24

2.7

10

648

Roof

100

0.38

10

380

Heat gain from walls, windows, and roof'1'

Infiltration heat gain'2'

Heat gains from persons'3'

Heat gains from lighting

Heat gains from electrical equipment'4'

Cooling load_

1537 1930 536 300 300 4600

[2] Infiltration heat gain = Volume of floor x Infiltration x Air density (1.143 kg/m3) x Ah( air).

[3] Heat gain from person = Number of person x Sensible/latent load per person (134 W).

[4] Heat gain from lighting = Number of lamps x Power of the lamps

• For the first condition, hourly average temperatures for 23 years were figured out and referred to as average temperature condition (ATC).

• For second condition, degree-hours values were computed for the warmest year and referred to as maximum temperature condition (MxTC).

• For third condition, degree-hours values were computed for the coldest year and referred to as minimum temperature condition (MnTC).

The cooling loads are determined using degree-hours method for three conditions (as listed above in the forms of ATC, MxTC, MnTC) according to every hour in each day. The calculation results are given in Table 7.2.

Moreover detailed calculation of the cooling load for 10 hours is demonstrated in Table 7.3 for 23-25°C by considering the total heat gain via temperature difference, infiltration, electrical equipment, etc. As the indoor temperature is taken between 20-25°C, the change in degree-hours value for different conditions is found and given in Table 7.4.

Annual cooling load is calculated considering the total heat gain via temperature difference, infiltration, and electrical equipment. The COP value of the absorption system selected for cooling at 75°C generator temperature is 0.4 (Fig. 7.4). Table 7.5 gives required cooling load and needed geothermal energy for three conditions in the temperature range of 20-25°C.

Table 7.3 Heat gains calculated for various indoor temperatures ranging from 23 to 25°C.

Hours

Temperature (oC)

Infiltration

Walls, windows, and roof Persons, lighting, and electrical equipment Total (kW)

Infiltration

Walls, windows, and roof Persons, lighting, and electrical equipment Total (kW)

Infiltration

Walls, windows, and roof Persons, lighting, and electrical equipment Total (kW)

Heat gains for 25oC

Heat gains for 23oC

16:00 17:00 18:00

28.66 27.97 26.86

0.706 0.573 0.359

0.560 0.454 0.285

1.136 1.136 1.136

0.899 0.766 0.552

0.713 0.607 0.438

1.136 1.136 1.136

2.748 2.509 2.126

0.745 0.591

Table 7.4 Degree-hours for various indoor temperatures ranging from 20 to 25°C.

Indoor temp ( oC)

20 oC

21 oC

22 oC

23 oC

24 oC

25 oC

April

208

143

92

51

28

16

May

529

390

280

195

132

85

June

2799

2364

1976

1622

1308

1036

July

2546

2016

1608

1251

940

671

Degree-hours

August

2715

2166

1731

1357

1033

751

for the ATC

September

1895

1495

1145

845

594

392

(oC -hours)

October

347

246

165

109

69

43

Total

11039

8820

6997

5430

4104

2994

Indoor Temp ( oC)

20 oC

21 oC

22 oC

23 oC

24 oC

25 oC

April

166

102

60

33

15

5

May

543

364

224

120

50

17

June

1814

1312

1003

736

510

335

Degree-hours

July

2963

2519

2071

1672

1318

1014

for the MnTC

August

1566

1232

944

708

508

346

(oC -hours)

September

1444

1115

876

671

499

361

October

342

340

234

153

101

64

Total

8838

6 984

5412

4093

3001

2142

Indoor Temp ( oC)

20 oC

21 oC

22 oC

23 oC

24 oC

25 oC

April

546

411

302

220

160

113

May

1829

1536

1273

1038

833

652

June

2399

1995

1638

1325

1051

815

Degree-hours

July

3553

3266

2653

2142

1710

1330

for the MxTC

August

4228

3862

3259

2719

2240

1818

(oC -hours)

September

3712

3112

2588

2131

1730

1375

October

880

669

513

401

316

243

Total

17147

14851

12226

9976

8040

Heat Medium Inlet Temperature (°C) Fig. 7.4 Cooling capacity factor profiles (modified from Yazaki Energy Systems, 2008).

Coolin

g Wate

r Inlet T

emp.

^6.6'C 29.4°c

1

îpc

/

The COP value of the HVAC system for cooling changes generally in the range of 2.5 and 3.5. In this study, COP value is taken as 3 for conventional cooling system. Electricity requirement for this cooling system is found to depend on the cooling loads and COP value, using the following equation:

where Qc represents cooling load of the residence in kWh and W represents electrical work in kWh. Annual cooling load and electrical energy requirement for the residence are given in Fig. 7.5.

Table 7.5 Cooling load and geothermal energy requirement for three different conditions.

Inside temperature (oC)

20

21

22

23

24

25

Cooling load (kWh)

ATC

5465

4829

4272

3782

3353

2984

MnTC

4793

4285

3847

3470

3145

2881

MxTC

7163

6358

5643

5022

4487

4006

Required

ATC

13662

12073

10680

9455

8383

7460

geothermal

MnTC

11982

10713

9618

8674

7864

7202

energy (kWh)

MxTC

17907

15895

14107

12554

11216

10015

Temperature (°C)

n Cooling load for ATC 3 Cooling load for MnTC ¡1 Cooling load for MxTC H Electricity for ATC EJ Electricity for MxTC Electricity for MxTC

Temperature (°C)

n Cooling load for ATC 3 Cooling load for MnTC ¡1 Cooling load for MxTC H Electricity for ATC EJ Electricity for MxTC Electricity for MxTC

Fig. 7.5 Cooling load and electricity requirement.

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