Selecting Air Conditioners

24 July 2018

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1) Update: 15 December 2021: Straight payback for Added Cost

Air conditioners are common household items nowadays in Singapore.  There are many different types and brands in the market and selecting the right type can be a headache for some,  particularly those new apartment owners. This article will help these users understand the various type and main differences between them so that they could select the correct type.

Types of Air Conditioners

Generally,  air conditioners for the resident units can be divided into window air conditioning units and split air conditioning units.   

Among the window units,  there are the window-mounted,  wall-mounted window unit, or casement window units. 

Among the split air conditioning unit,  there are single split or multi-split air conditioning units.  Then,  there is also a ceiling-mounted type which will not be covered here.

  Differences Between Window Unit or Split Unit Air Conditioning 

Detail Descriptions	Window Units	Split Units	Multi Split Units
1.  Type	The cooling and compressor or condenser units are integrated	The cooling and compressor or condenser units are separated and linked by copper pipes	It is the same as Split Units except up to 5 Indoor units can be connected to one outdoor unit
2.  Installation	Usually installed under or next to the windows,  at arm’s or lower than arm’s level.	Usually installed above the window or at the ceiling with outdoor units on a ledge or stainless steel support just outside the windows	The indoor units are connected to the outdoor unit via copper pipes through a control valve integrated with the outdoor unit
3.  Pipings	Not required	Insulated pipings are usually hidden inside PVC trunking running along the walls	Same as Split Units
4.  Power point	Required	Required with additional wiring for outdoor units running together with pipings in trunkings	Same as Split Units
5.  Noise control	Can be quite noisy	Only the outdoor unit runs a bit noisy.   Indoor units are rather quiet.	Same as Split Units
6.  Cost	About 30% cheaper than split units	Total cost would be cheaper than multi-split	Total cost would be more expensive
7.  Energy Consumption	For the same type of compressor i.e. inverter vs inverter,  cheaper to operate	Higher consumption because of piping thermal and pump head losses.  Losses in pipe around 10 watts per metre run.	Energy consumption can be high if long pipings are required;  also,  the control valve may not control refrigeration flow properly if the valves are faulty.
8.  Verdict	Cheap and efficient for the same type except the operation is noisy	Good only when one has adequate space for separate outdoor units	Can save space of the outdoor unit

 

 What to look for When Selecting  Efficiency Air Conditioner?

One of the most important factors in selecting an air conditioner is based on energy consumption or how much electricity the air conditioners will consume.  In Singapore,  it is mandatory in some countries that each air conditioner unit must have the following energy label so that the consumers can choose the right air conditioners.  Naturally,  the more the “Ticks”,  the more efficient will be the unit but for the higher the cost.  The consumers can also compare the annual energy cost which is specified in the label before they buy the right type of air conditioner. 

 Inverter vs Non-inverter

Air conditioners with "Inverter" are generally able to save more energy than the "Non-inverter air conditioners.  This is because the inverter air conditioner has load capacity controls that can control the speed of the motor to respond to the air conditioning load.  If the load is high,  the motor will run at full speed;  otherwise,  it will reduce the speed to save energy.   The non-inverter control can only start and stop the motor between high and low and low air conditioning load.  

The word "inverter"  is a jargon often used in electronic engineering to describe an electronic device that can convert AC supply to DC supply in order to control the speed of DC motors that are used in air conditioners.  There are also other kinds of energy-saving air conditioners using other kinds of technologies that might not have found footings in the market.

Basic Consideration

 1.  Whether to install split air conditioners or window unit air conditioners for energy-saving depend much on the design.   Basically,  if both air conditioning units of the same power and type (inverter vs inverter)  should consume the same amount of energy with split units consuming slightly higher power because of the heat losses through the longer refrigeration piping.  On the other hand,  if the window unit is badly designed without proper segregation between cooling and air intakes, it can consume higher energy.  Window units generally are noisier.

2.  Whether to install a multi-system or several single split systems will depend much on the air conditioning usage and the heat load of the cooling space.  Multi-system usually have control valves distributing refrigerants to various rooms; it will consume more energy in empty rooms as these control valves do not always work efficiently to cut off refrigeration flow completely especially after some years of operation.  For example,  if one installed a  system-3 to always cool only 1 bedroom most of the time,  it will not only cost more but also consume more electricity than 3 individual split units.  

Cooling Power Selection Guide 

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 Update 16 December 2021

Straight payback for Additional Cost

Newer air conditioners will be more energy efficient for reasons that there might be some innovative improvements made to the design of the air conditioners.   There might also be better material being used to improve efficiency.  If one has been using the air conditioners for quite some years,  it may be time to consider replacing the air conditioner.  Also,  if one decides which brand to use,   one should examine if it is worth the while to spend the additional sum to get a better and more energy-efficient air conditioner.

For those who are interested to find out more,   here is an example to use.   The attached table works out the cost-effectiveness between 2 popular brands using inverter technology and one other brand using conventional technology.   The table uses the power consumption and the coefficient of Performance given by the manufacturers.   One could use the table as an example to work out a similar table for other types and sizes of air conditioners.

Notes:

1.  The Coefficient of Performance (COP) is a SI unit measurement of energy efficiency used widely in many countries.  It is equivalent to the Energy Efficiency Ratio (EER) in use in the US.  COP is defined in terms of cooling power in watts per watt of electricity input and EER is in Btu/hr per watt of electricity input.  A COP of 1.0 equals EER of 3.4.    This is because  1 W is equal to 3.412 BTU/h or 1 KW is equal to 3,412 BTU/h.

For the convenience of the readers,   the attached Google sheet will help to calculate the payback of the additional cost of selecting a more efficient air conditioner which will be more expensive.  Please place selected air conditioner in column D

Reference:

1)  Mitsubishi Technical Data for MSY-GN10VA

2)  Panasonic Technical Data for CU-PS9UKZ