Airflow (CFM) Determination of an air-water heat pump (ASHP)

If you are a HVAC / R technicians, you should always check the heat pumps (ASHP) for adequate ventilation through the coils in troubleshooting or preventative maintenance.

Proper air flow is crucial for the operation of ASHP. Part of the heat transfer is determined by the flow of air over the coils inside and outside. If the airflow is incorrect, then the heat transfer is wrong and can drastically affect the equipmentPerformance.

1500 Watt Amp

Accurate flow measurement is important for the resolution of a heat pump system. In fact, no test is valid if the cooling flow is not correct!

ASHP manufacturers to follow the tenants of air conditioning, heating and cooling Institute (AHRI), a "value test" requires a percentage of the volume of air, if you have divided on the extent of indoor air-side capacity, may not exceed The 37.5 SCFM per 1000 BTU / h [This is a maximum of 450 cubic metersFeet per minute (CFM) of air power] on an internal battery for 12,000 BTU / h capacity. Most manufacturers use an acceptable range 350-450 CFM to 12,000 BTU / h capacity, and more than 750 CFM to 12,000 BTU / h capacity external battery (most external fans to move about 1,000 CFM to 1500 CFM to 12,000 BTU / h capacity). In the HVAC / R industry 12,000 BTU / h as a "tone" of cold is called. In general, most producers of about 400 CFM to fire "tone"in the evaluation of their equipment.

Before a determination of the airflow always check that all the stops and open mesh filters and coils are clean and the vents and fans are running properly ensures a flow of air through the coil internal and external battery.

There are several methods to determine the amount of air flow through a coil inside to help. The internal battery is controlled in the rule, because the flow of air must pass through this coil, so that the refrigerant can be absorbed (ASHPCooling) or reject (ASHP heating) the heat corresponding to the "sinking". In summer, the "pit" in the open air in winter is the "pit" in it.

One of the most commonly used in the revised ASHP air flow is the method of "heating" of the auxiliary or emergency (backup) heater (s) were. This method can be performed regardless of outside temperature.

In carrying out this test, you should keep in mind that with a rule, the more air-source heat pumps operatethe same amount of air regardless of the mode. In heating or cooling or heat emergencies or defrost, the heat pump provides only the flow of "same" air per tonne over the internal coil. The only change is possible, during the cooling operation, as the formation of condensation on the internal battery, the resistance increases slightly, lowering the air flow is something. Of course you can also speed and volume settings for both CFM cooling or heating on some ASHPs.

The airflow (CFM), a check ASHPmust perform various measurements and using some 'math. The common formula for calculating the CFM is:

Emergency heat (BTU / h)

CFM = -----------------------------

Temperature rise x 1.08

You have a ton CFM-capita travel through the inner coil during cooling or heating mode. To achieve this, consider the system in emergency heat and place the thermometer in place of the supply air and exhaust air paths as close to the air handler as possible withoutinfluenced by the effect of radiant heating.

In the above formula is heat emergency CFM BTU / h. Since the warming is occurring, the calculation of electrical data. When searching Btu / h of heating power, simply measure the voltage and current in the separation of the heater (s) and record values. This requires the use of a voltmeter and an ammeter.

Power supply voltage multiplied by amperage. Power multiplied by 3.413(BTU per watt) is Btu / h and you have the formula for the counter value of CFM.

CFM in the growth formula, the denominator is derived from the temperature difference between the exhaust air for heating and air conditioning (s) is / are stabilized, and the difference occurred. This difference (sometimes referred to as TR or TA) is then found to be a constant of 1.08 for the set temperature difference multiplied. Always pay close attention to changes in temperature, if the searchTemperature difference.

The temperature difference is the denominator formula for CFM.

If the formula is complete with the necessary inputs, the answer is the total air delivered (CFM) travels through the heater emergency heat mode. Then you simply divide this value by the tonnage of the external battery installed at the find CFM per ton. The flow of cooling air (CFM) are close to this value or slightly lower due to the increased water pressure dropCondensation on the interior during the cooling coil. ASHP heating system air compressor (CFM) per ton, a value similar to those found in heat emergency. CFM per ton to be acceptable should reside in the AHRI range.

If the incorrect air flow (CFM volume) is on the inner coil (evaporator in cooling mode, the condenser in heating mode), this situation must be corrected before further analysis of the refrigeration circuit.

ASHP determine the air flow inside the coil (CFM) in case of emergencyExample of heat:

Two (2) Units of sound

Separated at 240 volts

20 amps to separate

Back Air = 70 ° C

Air = 88 ° C
CFM = (240 x 20 x 3.413) ÷ (1.08 x 18 ° F) = 843
CFM 843 tons to 2 tons = 421.5 CFM

(This amount is acceptable for AHRI)

You should also check the minimum distance for the outdoor coil unit manufacturers around the trees and shrubs for the bridges to allow adequate heat dissipation in the summer andPower consumption in winter. You can also determine the flow of air over the external battery through the use of specific manufacturer's product, as shown below. Most ASHP external battery is usually around to provide that amount when the coil is installed properly and freely.

Phillip A. Rains

Airflow (CFM) Determination of an air-water heat pump (ASHP)