Unit Operation; Air-To-Air Cooling Products (Air Conditioners); Air-To-Air Cooling And Heating Products (Heat Pumps); Cooling Mode - Bard Q-TEC Q A4D Series Installation Instructions Manual

Unit Operation

Air-to-Air Cooling Products (Air Conditioners)

The cooling mode operates similar to a refrigerator, removing heat from inside the conditioned space and rejecting it
outside of the space being controlled. There are three main parts of the system:
1. The evaporator (indoor) coil where cold refrigerant absorbs heat from the air, which circulates from the
conditioned space through the machine and is returned to the space at a lower temperature and with some
of the humidity (moisture) removed. The moisture exits through a condensate drain system. A motor/blower
assembly moves the indoor air through the system.
2. The compressor, which is a sealed pump that moves the refrigerant through the system.
3. The condenser (outdoor) coil where the heat that was absorbed from the indoor space is discharged to the
outdoor environment. A motor/fan system moves the outdoor air across the condenser coil. A properly sized
air conditioner cannot cool a structure off rapidly and instead will pull down the temperature slowly. It also
will remove a certain amount of moisture (humidity) from the circulating airstream in the process. It may take
several hours to pull down a hot, moist building or structure on initial startup or anytime the system has been
turned off for a long period of time. It is generally best to set the thermostat at a comfortable temperature and
let it control the system as needed, rather than turning it on and off.
Moisture (humidity) removal with a conventional air conditioner (cooling) unit, or heat pump when operating in the
cooling mode, is not directly controlled and is a by-product of the unit operating to control temperature in response
to the temperature (thermostat) control device. Oversized equipment can easily control temperature but will have
short run-times, thus reducing its ability to remove moisture from the circulating air stream.
There are also many additional influences that can affect humidity levels within the conditioned space such as
laundry appliances, cooking, showers, exhaust fans and any other items that can generate moisture or affect its
removal from the space. Therefore, while operation of the air conditioning or heat pump system in the cooling
mode will remove some amount of moisture as it reduces the air temperature, precise humidity regulation in the
conditioned space cannot be assured and additional equipment such as a dedicated dehumidifier may be required.

Air-to-Air Cooling and Heating Products (Heat Pumps)

A heat pump is a refrigerant-based system that has additional components and controls that both heats and cools
using a compressor for both modes of operation. Most heat pumps will also be equipped with some amount of
electric heat to supplement the heating capacity of the compressor system on an as-needed basis. This operation is
entirely automatic and is controlled by the indoor thermostat and possibly also an outdoor thermostat.

Cooling Mode

The cooling mode of a heat pump is exactly the same as that described for an air conditioner in the above section.

Heating Mode

The system operates in reverse cycle, meaning that it absorbs and moves heat from the outdoors and transfers it
indoors to be rejected into the circulating air stream. Even though it seems cold to humans, there is usable heat
that can be extracted efficiently from the outdoor air down to 0ºF, although the colder the air is there is less heat to
extract and the operating efficiency is diminished.
Defrost Cycle
When operating in the heating mode, the outdoor coil will be colder than the outdoor air that is forced over it by the
fan system. When the outdoor air temperature is above approximately 40°F, moisture can accumulate on the coil
and it will drain down and out the base of the unit. As the air temperature gets below approximately 40°F, the coil
temperature will start to drop below 32°F, and frost or ice will begin to form on the coil.
An automatic defrost system keeps track of system run time when the outdoor coil temperature is in the freezing
zone and will initiate a defrost cycle at the appropriate time. The unit continues to operate during the defrost cycle,
but the outdoor fan motor will stop and the reversing valve will shift positions to flow hot refrigerant gas through the
outdoor coil to melt the accumulated frost. Water will start to drain freely from the unit, and steam may be emitted
from the unit.
The length of the defrost cycle will vary depending upon actual outdoor temperature, humidity levels and amount
of accumulated frost. It could range from 1-2 minutes up to but not exceeding 8 minutes. When the defrost cycle
Manual 2100-034G
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Unit Modes of Operation