Programmable thermostat is used extensively in medium to high end HVAC systems. The common thermostat that is used in the air conditioning control system before the advancement of microchip and electronic is a simple mechanical bi-metallic thermostat that contact before a set temperature is achieved and disconnect after a set temperature is achieved.
A dead band of few degrees known also as hysteresis is set to prevent chattering of contact that can cause damage to the load that is being controlled. This simple thermostat has greater tolerance and is not accurate. The tolerance can be as high as +/-5°C.
The advancement and the reduction of microchip price have enabled the HVAC industry to use better electronic control that is more accurate, more user friendly and efficient. Products that incorporate Liquid crystal Display, 7 segment LED display, LED, keypad/touch screen and better industrial design have been developed.
The programmable thermostats that have been certified by the government have many features that allow you to save energy. When used properly, it can save your utility bills and provide better comfort to you. If you are looking for one, make sure that the thermostat has the ENERGY STAR mark on it.
Features Of Programmable Thermostat
● 7-Day Programmable Schedule feature will enable you to program the ON/OFF time, temperature setting, mode of operation and other important features. This will enable the proper use of the air conditioner capacity. For instance, when there is no one at home, the set temperature will be set higher during that duration to reduce the electricity consumed.
● Night Setback feature will increase the set temperature (if in cooling mode) after certain hours gradually as one will not need that much cooling capacity once you are sleeping. This feature is sometimes incorporated into the programmable schedule.
● Thermostat accuracy of +/- 2°C or better to ensure the comfort of the occupants in the house.
● 24 Hour Clock is a must with liquid crystal display, keypad/touch screen, backlighting that enables you to operate it in the dark.
● Holiday feature option need to be there. During holidays, the set temperature will be set higher(in cooling mode) or cycling mode to reduce the capacity and hence the consumption of electricity.
● Actual Outdoor or Indoortemperature display option is another good feature to have.
● Diagnostics feature that enables you to find out the reason the air conditioner is not working properly. It could be a missing sensor, high pressure tripping, low refrigerant, etc.
● Air Filter Change indicator after a certain time of operation. This reminder is a good feature to alert you that it is time to change or clean your filter.
Installation
When installing the thermostat, remember to install the sensor in a location where the air circulation is good. Usually the sensor is located at the panel itself. Do not install it under direct sunlight, doorways or windows as this will cause inaccurate reading of the room temperature.
Air Conditioner Refrigerant
How does air conditioner refrigerant affect our environment? All of us have probably heard about the ozone layer which is located 35 miles above the ground. This upper layer of our earth's atmosphere protects the earth from the sun's ultraviolet rays by reflecting them back to space. UV rays are harmful to the plant, marine life and human beings on the earth.
How does air conditioner relate to the ozone layer? It was discovered in the mid 1980s that the commonly used air conditioner refrigerant has a damaging impact on the ozone layer.
At that time, the refrigerants that used then were known as CFC(chlorofluorocarbons) and HCFCs(hydrochlorofluorocarbons). CFCs are a family of chemicals that contain chlorine, fluorine and carbon. The chlorine content in these compounds cause the depletion of the ozone layer.
R410A Refrigerant
This discovery prompted the signing of Montreal Protocol of 1987, an agreement signed by 180 nations that target to phase out the production of CFCs by 1995 and HCFCs by 2030. New refrigerants that are being used to replace these CFCs are HFCs(hydrofluorocarbons) and refrigerant blends(Azeotropic, Zeotropic). In summary, the 4 commonly used refrigerants that you can find today are:
● CFCs
● HCFCs
● HFCs
● Refrigerant blends
The future commonly used refrigerants will be in the last two categories. Among the currently widely used ones are R-134a, R407C and R410A.
More discovery on the causes of global warming had prompted many countries to sign the Kyoto Protocol in 1997. The main reason this was being done was to reduce the greenhouse effect caused by man-made greenhouse gas emissions.
Greenhouse gases include:
● Carbon dioxide
● Nitrogen dioxide
● Carbon monoxide
● CFCs, HCFCs, HFCs
● Ozone
● Methane
● Water Vapor
In the field of HVACR, newer refrigerant such as R32 has been widely publicized as a replacement for R-410A and R-407C as this gas has a lower Global Warming Potential. Lower GWP will reduce the greenhouse effect hence reducing the global warming effect. Many manufacturers are beginning to design and develop HVAC equipment using this refrigerant.
Do your part to preserve mother nature...
CFC Refrigerants
These refrigerants were developed more than 70 years ago and are harmful to our respiratory systems and the ozone layer. Their production was stopped since 1995 but are still being used widely in existing residential air conditioning units as many equipments have a lifetime of up to 30 years. Today's refrigerants used are from reclaimed units that are no longer in operation. The common ones still used are:
● R-11 CCl3F
● R-12 CCl2F2
● R-113 CCl2FCClF2
● R-114 CClF2CClF2
● R-115 CClF2CF3
HCFC Refrigerants
These air conditioner refrigerant is considered partially halogenated as they consists of methane or ethane in combination with chlorine and fluorine. They are shorter lifespan and are less destructive to the ozone layer compared to CFCs.
They are an interim solution to a totally "free from chlorine" refrigerant that are being developed. Their production are scheduled to be phased out totally in 2030. The common ones used are:
● R-22 CHClF2
● R-123 CHCl2CF3
R-22 is used extensively in residential, commercial and industrial applications. The schedule of phaseout :
● 2015 - Production freeze and use limitations
● 2020 - Prohibited for new air conditioning and refrigeration use
● 2030 - Total phaseout
HFC Refrigerants
These air conditioner refrigerant contain no chlorine atom and is not destructive to the ozone layer though they have a slight effect on global warming. R-134a is used in new systems that are specially designed for its use. The common HFCs are:
● R-134a CH2FCF3
● R-125 CHF2CF3
The 1997 Kyoto Protocol puts R-134a as one of the 6 greenhouse gases that must be reduced. There is no phaseout date for this refrigerant and it is expected to be highly used in the HVAC industry.
Refrigerant Blends
These air conditioner refrigerant are also known as "azeotropic" and"zeotropic". Their use is increasing as they are environmental friendly. The setback is that the total air conditioning systems production cost is higher.
However, as more manufacturers switch to this type of refrigerants, the cost/unit will drop eventually. The common refrigerant blends used in the air conditioning industry are:
● R-410A CH2F2/CHF2-CF3
● R-407c
R-410A are used as a replacement refrigerant for residential air conditioning applications.
R-407C are used as R-22 replacement.
Recovery, Recycling and Reclaiming of Refrigerants
Laws have been passed to prevent the release of CFC refrigerants into the atmosphere. The steps taken are:
Recovery
The act of removing the refrigerant from a system and store it in an external container. No testing or processing is needed in any way
Recycling
Refrigerant is cleaned for reuse by oil separation and passes though devices such as core filter-driers. This procedure reduce the moisture, matter and acidity of the refrigerant for reuse. It is usually done for jobs on the field or service shops.
Reclaiming
Reprocess the refrigerant to new product specifications which may include distillation process. This can only be done by manufacturing plants where chemical analysis is required. Highly equipped local service shops may have this facility as well.
Consumer Role
How can consumer like you play your part in the effect to keep our earth green? You can do that by purchasing air conditioning systems that uses new refrigerant such as R-134a, R-407C or R-410A.
Most equipment are labelled with stickers that indicate the type of refrigerant used. Examples are "ozone friendly" sticker or "R-410A" sticker.
If the HVACR equipment is available, choose lower Global Warming Potential refrigerant such as R32 to help reduce the greenhouse effect compared to if you were to use a higher GWP refrigerant.
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