24 | Air-conditioning and Refrigeration

This is electrical apparatus which is can be found everywhere in residential, office buildings and factory in every cities. The air-conditioner is widely used in Asian countries as we are all located at the hot zone. The air-conditioner needed to cool down every homes, offices and buildings factories. This electrical apparatus is an essential for people to working in comfort and cool space.

System components

The air-conditioner principles is actually mechanical systems. The basic component of air-conditioner unit is listed below.

compressor unit (heart of air-conditioner unit) - change the freon gas from (LP) vapor to vapor (HP). The compressor is the heart to pump and compress the gas. Capacitor wired to the motor for start run the motor compressor.
condenser unit - this section is to convert the vapor into liquid state at HP conditions.
expansion valves - this device known as metering device, the narrow angle inside the device acts to change from HP liquid to LP liquid.
evaporator unit - this section blow the LP liquid and used the room ambient temperature to blow the evaporator coil to produce cool air out. This action then change the state from LP liquid into LP vapor and returns to the compressor unit and repeat the same cycle.
Freon gas (or aircon gas) - R22, R410A, R32, R134A
Close circuit pipes - commonly copper tube are used. For higher pressure gas, aluminium pipes are been used due to capability to withstand high pressure (HP).

Figure above showing basic air-conditioner components.

Low pressure (LP) - cold, High pressure (HP) - hot

Types of air-conditioner unit

Type available in today's market.

window unit
split unit
ceiling or wall cartridge system
chiller water system

All types of refrigeration system and air-conditioner unit have the same characteristic. Two parts of air-conditioning principle works with a close circuit piping (aluminum or copper)

Out door unit

The outdoor unit consist of following part:

Fan blade and motor,
condenser coil,
expansion valves,
compressor motor.

This outdoor unit are commonly installed outside building structure and mounted according to the indoor unit. The component must width stand high temperature under sunlight during the day. The outdoor can bring dust if the premise is nearby roads, or somewhere area is heavy pollution industrial area.

Indoor unit

This indoor unit consist of following part:

DC motor,
controller/receiver board,
evaporator coil,
air filter,
drain pipes,

This indoor unit is also known as fan coil unit (FCU) and the supply operates using DC voltage on the remote circuit board and fan motor. DC supply operates quieter compares to AC fans. The speed of the fan is automatically adjusted by temperature sensor inside the control card.

Gas or Refrigerant Agent used in Air-conditioning System

The most common refrigerant in the past was a CFC, most commonly called as Freon.

Type of gases or freon used in air-conditioning system:

R32
R410 or R410A
R22 (obsolete, no more in production)
R134A (for vehicle)
R717 ammonia

R32

R32 refrigerant gas is a pure HFC, with zero impact on the ozone layer and low global warming potential, used in its pure form in new small air-conditioning and refrigeration equipment as well as having being commonly used as a component in various HFC mixtures.

R32 is developed by Danfoss and has lowest GWP and zero ODP . Daikin has exploring its use in Japan . The only issue with R32 is its flammability classification of A2 Mildly flammable. R32 refrigerant has GWP (Global warming potential) of 675 which has three times lower GWP than R410A (2088). However this R32 can produce more energy and cooler efficient compare to R410A.

R32 is a better choice for the environment and will give an extended service life due to the price and availability of the refrigerant. R32 is not explosive, is extremely difficult to ignite and is the least toxic of all the Class A (non toxic) refrigerants listed in ISO 817. Because R-32 efficiently conveys heat, it can reduce electricity consumption up to approximately 10% compared to that of air conditioners using refrigerant R-22. Furthermore, compared to the refrigerants widely used today such as R-22 and R-410A, R-32 has a global warming potential (GWP) that is one-third lower and is remarkable for its low environmental impact.

R410

R-410A is often referred to as Puron, the main brand name associated with this type of refrigerant. It is a hydro-fluorocarbon (HFC) which does not hurt the ozone layer.

Forane® 410A refrigerant (R-410A) is a non-ozone depleting, near azeotropic refrigerant blend of hydrofluorocarbons (HFC) R-32 and R-125 developed for use in air conditioning applications. Genetron R410A, Puron, and Suva 410A is a zeotropic, but near-azeotropic mixture of difluoromethane (CH2F2, called R-32) and pentafluoroethane (CHF2CF3, called R-125).

R410 is much safer and being extensively used in VRV ( Variable Refrigerant Flow) machines. R410 is competent and release heat efficiently. It is environment-friendly.

R134a

R134a is also known as Tetrafluoroethane (CF3CH2F) from the family of HFC refrigerant. Currently it is also being widely used in the air conditioning system in newer automotive vehicles.

It is now being used as a replacement for R-12 CFC refrigerant in the area of centrifugal, rotary screw, scroll and reciprocating compresssors. It is safe for normal handling as it is non-toxic, non-flammable and non-corrosive.

R22

R22 is going to be phased out due to phased out due to its ODP( Ozone Depletion Potential) and GWP ( Global Warming Potential ) values. Chlorodifluoromethane or difluoromonochloromethane is a hydrochlorofluorocarbon (HCFC). This colorless gas is better known as HCFC-22, or R-22. It is commonly used as a propellant and refrigerant.

Properties of R22 gas

The R22 has a boiling point of -40.7°C, developed primarily for low-temperature systems.
This gas was used extensively in domestic, commercial as well as industrial low-temperature systems to evaporator temperatures as low as -87°C.
Both atmospheric pressure and discharge temperature are higher compared to R12, but power requirement is comparatively the same.
Evaporator temperatures are between -28 to -40°C.
The ability of r22 to absorb moisture is comparatively greater than r12, therefore, less trouble due to ice formation.
Fluorocarbon based refrigerants are safe.

R717

Ammonia is still, without a doubt, the most important industrial refrigerant in the present day because of its good thermodynamic properties and it’s cheap. Ammonia is one of the refrigerants most commonly used in the absorption-type air-conditioning systems. Ammonia vapors are absorbed quickly by large amounts of cool water. In fact, it can absorb vapor as quickly as a compressor. Due to its high toxicity and flammability, an industrial application using ammonia requires strict regulations.

Ammonia is not compatible with copper and its alloys, so refrigerant piping and components have to be made of steel or aluminum.Ammonia has a lesser density compared to air, so in case of any leakage, ammonia mixes into the atmosphere.If the industrial plant is built outside or on the roof of a building, the escaping ammonia can easily drift away without harming the occupants.

Ammonia can be detected by its odor at very low concentrations, and this acts as an early warning signal.The safety aspects of ammonia plants are well known, and there is a reason to expect a continued increase in the use of ammonia as a long as refrigerant exists.

Ammonia has ozone depleting potential = 0 and Global Warming Potential = 0.

The Benefits of R32 vs R410A

Zero ODP
One third of R-410A GWP.
Required less charge as it has a 20% higher volumetric capacity.
Similar saturated pressure hence development is easier.
Higher critical temperature hence higher COP.
Lower density hence the amount of charge required is smaller.
Single component of gas, therefore it is easier to be produced and managed.

The Disadvantages of R32

Toxicity level slightly higher and more precaution is needed to use it.
Higher discharge temperature will cause oil degradation in the compressor which may damage some of the components in it. Design consideration is required to ensure the discharge temperature is limited to an acceptable level.

Cooling Capacity Units

British thermal unit (Btu or BTU) is a traditional unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

Room sizing and cooling calculations

To estimate the amount of air conditioning you will need for your daytime living area, you will first need to find out its area. You will need to find the length and width of each room and multiply them. Then, you have to add the area of each room together for the total. This figure needs to be in square metres.

Factors affecting room calculations:

sun shine into the room and directions on wall or window.
number of person using the room. size of person big or small.
heat source from various appliance or equipment in the room.

Chart for calculations of room sizing.

Chart for room sizing and cooling .

Example calculations:

Refer to figure on right, calculate the room sized 25 feet (L) and 18 feet (W)? This room have a door entrance and a small window and the sunlight shines the room through the window in the morning only. Total occupants in this room is only one person. Calculate the total BTU and sizing of cooling capacity.

Solution:

BTU = L x W = 18 ft x 25 ft = 450 sq.ft

Refer to chart the BTU shall be 14,000 BTU.

+ small window +500

+ human body +500

Total room cooling capacity is;

14000 + 500 + 500 = 15,000 BTU

Cooling capacity to Power unit (Watts)

Formula: 1 watt = 3.41 BTU/hr

Example calculations: Given a room installed with a 13,000 BTU air-conditioner unit, calculate the power rating and current drawn by it.

Solution:

Electrical power, P = BTU ÷ 3.41 = 13000 ÷ 3.41 = 4,105 watts

Current drawn is ; I = P ÷ V = 4105 w ÷ 240 v = 17.1 ampere

The height of ceiling affects where higher ceiling means more power to cool the room, therefor slower cooling the room.

If the ceiling is lower, then the cooling up the room will be faster.

Protection rating for air-conditioner circuits

According to Wiring regulations, each air-conditioner unit shall be protected by miniature circuit breaker (mcb) or fuse.

Standard rating :

minimal 16A MCB or 15A fuse cb for AC unit ranging from 2000w ~ 3500w or c.c 9000~ 13,000 BTU
20A MCB AC unt ranging from 3500w ~ 4800w or c.c 13,000 BTU ~ 16,400 BTU
32A MCB AC unit ranging from 4500w ~ 7600w or c.c 16,000 BTU ~ 25900 BTU

Warning: Do not install air-conditioner unit without knowing the specifications.

It is not recommended to use ring circuit socket outlet (SSO) 13A to get electric supply to the air-conditioner unit.
Sometime air-conditioner may operate overload and the 32A MCB under ring circuit may not able to detect the fault.

Global Warming Potential (GWP) Chart

Common air-conditioning problem encounter

The followings are the common problem:

motor at compressor fail to run - due to capacitor faulty or compressor motor coil problem.
icing at expansion valves - due to blockage at expansion valve.
no cold air coming out from evaporator unit (FCU) - low on Freon gas, filter dirty.
FCU kept shuting down - possible due to PCB board or other sensor at fault.
Vibrating on outdoor unit - unit not install properly or slanted or mechanical fastener faulty or loose.
No cold - possible low on gas or leakage on the piping circuits.
smelly air - when air-conditioner is running, possible due to pipe leaks at condenser side or evaporator coil.
remote control won't responds - remote faulty or battery weak

System package Air-conditioner Installation

Installation of the air-conditioner are more expensive if the pipes is further from the compressor unit. This because of the cost on the copper pipes and it insulation material required to cover along the piping route to FCU.

System 1:1

1 compressor and 1 indoor unit
This method installation is sometime known as back to back if outdoor unit is nearby.

System 1:2

1 compressor and 1 indoor unit
This known as 2 indoor and 1 outdoor unit. When there are two rooms sharing with one compressor unit.

Building Centralized Air-conditioning System

Figure above showing building air-conditioning system known as centralized air-con system.

The chiller produce cold water and supply to all the air handling unit (AHU) through a cold water supply pipes (CWP) and then all the water will send to AHU unit (every section or every floor).
The cold water goes into the unit and the water drip inside the AHU box. The cool air will blow out by using centrifugal fan and send the air through all air ducts and finally to where air outlet into each room.
The water drip down to the AHU base and flow back to chiller unit by pumping the discharged water (not cold) back to the chiller unit and repeat the cycle again.

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