6.2 Experimental Analysis
6.2.2 Air Conditioning Units
In the tropical area and especially the summer time, high relative humidity, elevated air temperatures, and bright sunshine can sometimes combine to produce an uncomfortable indoor environment. An air-conditioning system can provide comfort for occupants by lowering the air temperature and the humidity level in the home. Two HVAC units are used in this study.
Conventional ON/OFF cycle HVAC unit is installed in house #3305 and VFD HVAC unit is installed in house #3307. The two units have some common terms we will come across then comparing and determining the best choice for air conditioners:
1. The refrigerant is a substance that circulates through the air conditioner, alternately absorbing, transporting and releasing heat.
2. A coil is a system of tubing loops through which refrigerant flows and where heat transfer takes place. The tubing may have fins to increase the surface area available for heat exchange.
3. The evaporator is a coil that allows the refrigerant to absorb heat from its surroundings, causing the refrigerant to boil and become a low-temperature vapor.
4. The compressor squeezes the molecules of the refrigerant gas together, increasing the pressure and temperature of the refrigerant.
5. The condenser is a coil that allows the refrigerant gas to give off heat to its surroundings and become a liquid.
6. The expansion device releases the pressure created by the compressor. This causes the temperature to drop and the refrigerant to become a low-temperature vapor/liquid mixture.
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7. The plenum is an air compartment that forms part of the system for distributing warmed or cooled air through the house. It is generally a large compartment immediately above the heat exchanger.
6.2.2.1 The ON/OFF Cycle HVAC System
The schematic diagram for conventional HVAC system is described in Figure 6.4. The compressor (CM) and the blower (BM) are fed in HVAC unit by three phase system with VLL=230 V, connected to supply by compressor contactor (CC). The Fan motor (FM) is connected between two phases 230V and integrated with compressor motor. Electronic control board (ECB) is built for detecting and controlling the ON/OFF cycle unit. Thermostat device is connected to ECB to detect the setting and room temperatures. The CC and BMC is controlled by ECB continuously. Transformer 240V/12V is used to apply ECB and relays.
The unit was built and wired according to the Al-Zamil air conditioning standers and specifications. The main components of the ON/OFF unit, is the BLDC motor for the compressor, the ON/OFF frequency should be less than 250 cycles per day, which meant that the ON/OFF cycle shall not exceed on average of 10 times/hour. The set point of experimental study for the ON/OFF unit is fixed as 24 oC, and the condenser fan was set auto.
Table 6.2 Specifications of ON/OFF unit
Item Description
ON/OFF Run and stop operation.
Operation Mode Switches between Cool /Auto/Fan/Heat.
Temperature Setting The set point temperature for cooling in the following range: 15°C to 30°C.
Fan Speed Setting Fixed high or low or it can be auto.
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L1 L2 L3
CC BMC
CM FM
Fuse 230 Vac
230 Vac 230 Vac
Thermostat
BM
240 V
12-0-12 v
(ECB) Electronic Control Board IC
System(Yel)Lock(Red) Power(Gr)
HPS
LPS
UVM SD
CC PDS1
BMC
HC1
HC1 ASFTo OUT Fan
DIP Switch
Jumper To L2
Figure 6.4 Schematic diagram for ON/OFF HVAC unit
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We are given some reported data for the motors and the compressor of the ON/OFF unit which have investigated experimentally in our study. Table 6.3 is presented the energy consumptions for different outdoor temperature with several heat capacities in the house. The power consumptions and the input current have also listed in the Table 6.3.
Table 6.3 Experimentally test data for the ON/OFF unit
Outdoor °C Capacity Btu/hr Unit Capacity kW Power (W) Input current (A)
24 76000 22.274 5282 15.55
29.4 72100 21.132 5796 16.17
35 66500 19.489 6415 18.3
37.8 62300 18.258 7100 20
46 57900 16.968 7842 21.8
51.5 52965 15.522 8657 23.86
ON/OFF Unit Compressor Specifications
Table 6.4 shows the main specifications of the ON/OFF unit such as the unit model, voltage range and refrigerator type. Furthermore, the standard temperatures of the condenser, evaporator and return gas have also presented in the Table 6.4.
Table 6.4 Compressor data of ON/OFF unit
Compressor Information
Compressor Model ZP61KCE-TF5 Phase 3
Refrigerant R-410A,Mid Pt Frequency 60
Volts 200-230 Application Air Conditioning
RLA(MCC/1.4) (Amp) 21.2 MCC (Amp) 29.7
RLA(MCC/1.56) (Amp) 19.0 LRA (Amp) 123.0
Inputs
Condensing Temperature (°C) 54.4 Evaporator Superheat (°C) -6.6 Evaporator Temperature (°C) 7.22 Compressor Superheat (°C) -6.6 Return Gas Temperature (°C) 18.33 Total Sub-cooling (°C) -9.44
Results
Compressor Capacity (But/hr) 61,500 Refrigerant Flow Rate (lb/hr)
Net Refrigeration Effect (But/hr) 61,500 Current (Amp) 16.8
Power (W) 5,700 Isentropic Efficiency (%) 72.0
Compressor EER (Btu/Wh) 10.79 Liquid Temp (°C) 46
Condenser Heat Rejected (Btu/hr) 80,954
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The Table 6.5 provides information for the compressor which it’s varies as per condition of the outdoor temperature change by step of 5.5°C from 24°C to 51.5°C.
Table 6.5 Compressor power varying per outdoor temperature
Outdoor °C Power (W) Current (A)
24 3960 12.7
29.4 4400 13.7
35 4900 14.9
37.8 5500 16.3
46 6100 17.8
51.5 6800 18.6
According to Al-Zamil air conditioning Company, Table 6.6 shows the data of blower motor for ON/OFF unit.
Table 6.6 Blower motor data
Item Unit Stander Unit motor Value
Break Down Torque Nm 4.42 3.42
Locked Rotor Torque Nm 1.16 0.82
Rated Torque (Full Load) Nm 3.76 3.38
Rated Input Power (Full Load) Watts 798 742
Rated Current (Full Load) Amps 3.17 3.53
Locked Rotor Current Amps 6.57 5.04
According to Al-Zamil air conditioning Company, Table 6.7 shows the data of condenser motor for ON/OFF unit.
Table 6.7 Condenser motor data
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Item Unit Stander
Break Down Torque Oz.ft 50.75
Locked Rotor Torque Oz.ft 20.7
Rated Torque (Full Load) Oz.ft 50.4
Rated Input Power (Full Load) Watts 749
Rated Current (Full Load) Amps 3.59
Locked Rotor Current Amps 7.9
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