» Home
» Air Conditioner
» Translation
» Downloads
» Book Publishing
» Printing
» Health
» Cell Phone
» Weight Loss

Air Conditioner Installation Guidelines

INSTALLATION GUIDELINES

Heat pumps and air conditioners should be installed by knowledgeable technicians according to the manufacturer’s installation instructions and all national and local code requirements. General installation guidelines are applicable to most units and should be followed insofar as they do not conflict with these other requirements.

Proper air conditioner and heat pump installation can be achieved by addressing four critical areas:

• indoor air handler, especially the air flow over the fan-coil unit and through the forced-air duct system
• refrigerant system, especially the refrigerant charge
• outdoor unit, especially its air supply
• control system, especially the thermostat that turns the equipment on and off.

INDOOR AIR HANDLER

INDOOR AIR FLOW
For most heat pump and air conditioning equipment, air flow over the indoor coil should be 400 cubic feet per minute (cfm) per ton of air conditioning capacity (plus or minus 50 cfm/ton) when the air conditioner has been operating long enough to wet the indoor coil (usually about 15 minutes). If wet coil conditions cannot be obtained (e.g., installation during the winter), then air flow should be 425 to 450 cfm/ton (plus or minus 50 cfm/ton). In humid climates where removing humidity from the interior air is an important function, the best system efficiency may occur where the air flow is between 350 and 400 cfm/ton. In dry climates where little dehumidification is needed, the best system efficiency may occur when the air flow is between 400 and 450 cfm/ton.

Before indoor coil air flow measurements are performed, the duct system should be inspected and tested to ensure that leaks are minimized. Although no technique for air flow measurement currently has universal acceptance, the best flow measurement method available should be performed to verify and document that the air flow is within acceptable ranges.

There are several air flow measurement approaches:
• The most common technique involves measuring the static pressure across the air handler unit and using the manufacturer’s static pressure vs. flow rate curves for the air handler to estimate air flow. The manufacturer’s curves will

STATIC PRESSURES

To measure air flow

usually be based on the pressure between the return plenum and the area either before or after the indoor coil. Measuring the pressure before the coil is difficult, so it may be easier to calculate it by measuring the pressure after the coil and compensating for the pressure drop across the indoor coil.

This method can give good results if accurate pressure measurements can be made and flow curves are available. However, pressure measurements are often not accurate because pressures fluctuate significantly around the air handler unit fan and coil as a result of flow turbulence induced by the fan, abrupt changes in flow direction near the air handler, etc. Flow curves are often not available to technicians in the field, and curves developed for new fans and coils are often not applicable to fans and coils that have become dirty while operating in the field.

A variation of this method is to measure the static pressure across the indoor coil and use a flow curve supplied by the coil manufacturer to infer flow rate. Again, measuring the pressure before the coil is difficult and leads to errors.

• A second method is applicable just to heat pump systems equipped with supplementary strip heaters. The unit is operated with just the strip heaters on. The air flow rate can be calculated by measuring the temperature rise of air across the strip heaters and the energy consumption of the strip heaters and indoor fan [air flow rate (cfm) = 3.16 x energy use (watts)/.T (°F)]. The accuracy of this method depends on the accuracy of the temperature and energy consumption measurements. In making the temperature measurements, it is important that the air be well mixed where the temperature is being measured and that the temperature sensor be out of the line of sight of the strip-heat elements to avoid an inaccurately
high temperature reading due to radiative effects. The air flow measured using this technique must be corrected to wet coil conditions. Also, in some equipment, the fan speed during operation in the strip-heat mode is different from that during operation in the air-conditioning mode unless the thermotat and/or fan is properly configured by the technician for the test.

• Another method involves the use of flow hoods to measure air flow rates. In this approach, air flow rates are measured at the return registers or supply registers and added to obtain the total flow rate for the system. Researchers have found that many flow hoods used in residential applications in this manner are relatively inaccurate because of low air flow rates, non-uniform air flow through the flow hood, and other reasons. In addition, flow hoods underestimate the actual flow across the indoor coil when duct leaks are present.
• A new method that shows much promise for simplifying the measurement process while providing sufficiently accurate results is a specially designed orifice plate. The air filter in the system is removed and the orifice plate is inserted in its place. The pressure drop across the orifice plate is measured and used to estimate the system air flow rate using a flow curve for the orifice plate and a small correction factor for the different pressure drop induced by the orifice plate compared with the air filter. Non-uniform air flow entering the orifice plate (due to
bends in the return duct before the orifice plate) reduces the accuracy of this method. As with flow hoods, duct leaks make this method underestimate the actual air flow across the indoor coil if the air filter is not located at the air handler.
• A final, more costly and complicated method involves use of a duct blower to measure air flow. A duct blower is a device used to measure duct leakage in an air distribution system. It comes equipped with its own fan and a flow metering system. First, the pressures in the supply and return ducts are measured under normal air-conditioning operation. The duct blower is then connected to the return register or the air handler directly (blocking off the existing return) so that all return air flows through the duct blower. The equipment is again operated in its normal air-conditioning mode, with the duct blower fan operated so that the same pressures are achieved in the supply and return ducts. The flow measured through the duct blower is the same as the flow rate through the equipment during normal operation.

Source : U.S. DEPARTMENT OF ENERGY

Air Conditioner, Installation, Guidelines