To develop an understanding of the necessity of proper refrigerant line sizing and matching coil with condensing unit evaporator to obtain designed efficiency. It will also show the necessity of cleaning and maintaining heating and cooling equipment.

The students will realize the importance of looking at the total system and not just installing an outdoor unit to obtain high efficiency.

With today's higher efficiency equipment, it is imperative to properly match the indoor coil and the outdoor coil. A 12.0 SEER category condenser may only yield 10.0 SEER with a new coil that is not properly matched.

Cooling Heating

High Temperature HSPF Low Temperature

TWA060C TDC120B9V5
57.0 9.70 57.0 - 7.50 - - 8.4
TWA060C TWH048B14 57.5 10.80 56.0 - 7.75 - - 8.4
TWA060C TUC100B9V5
57.5 10.25 57.0 - 7.70 - - 8.4
TWA060C TUC100B9V5
57.5 9.85 57.0 - 7.60 - - 8.4
TWA060C TWV060P15-C 58.5 10.20 58.5 - 7.90 - - 8.4
TWA060C THD100A9V3
59.0 10.80 56.5 - 7.85 - - 8.4
TWA060C TWH060P15-C 59.0 10.50 57.5 - 7.80 - - 8.4
TWA060C THD100A9V3
59.0 10.30 56.5 - 7.75 - - 8.4
2-TWA030C TWE060B 59.0 9.60 59.0 - 6.75 - - 8.4
TWA060C TWV064E15-C 60.5 11.15 57.0 - 8.10 - - 8.4
TWA060C TWV064P15-C 60.5 10.75 57.5 - 8.00 - - 8.4
TWA060C TWH064P15-C 61.0 11.00 57.0 - 8.10 - - 8.4
TWA060C TWH064E15-C 61.5 11.40 56.5 - 8.25 - - 8.4
TWA072C TWE060C15-C 63.5 9.00 61.0 - 6.55 - - 8.4
TWA072C TWE060A 63.5 8.85 60.5 - 6.55 - - 8.4
2-TWA030C TWH062E15-C 64.5 10.85 62.0 - 7.35 - - 8.4
2-TWA030C TWV062E15-C 64.5 10.60 62.0 - 7.20 - - 8.4
No Footnotes Applicable to This Table
This (HTML Table) chart, a portion of page HP331 of the ARI Unitary Directory, August 1, 1992 - January 31, 1993, is reprinted by courtesy of the Air-Conditioning and Refrigeration Institute, ARI.

Proper refrigerant tube sizing is also imperative. Just as in moving water through a pipe, the same flow cannot be obtained through a 1/4" pipe as a 1/2" pipe. Today's units have compressors sized with no excess capacity and units are rated by ARI with only 25' of tubing. A job piped 50' with wrong tubing could drop SEER by 2%. Different tubing sizes are given for heat pumps and "cooling only" systems as well as evaporators above or below condenser. A refrigerant piping chart should always be consulted before any new equipment is installed. Heat pumps also have a max line set length as given by the manufacturer in the installation guide. Equipment manufacturers are also giving charging charts to weigh in refrigerant charge based on line size and length. This gives the technician the capacity to fully charge the system without starting it or having to spend time calculating super heat or subcooling.

Condensing unit efficiency is based on a specific evaporator coil match and must have correct connecting tubing to control refrigerant flow and velocity. Most manufacturers use 3/8" riffled tubing in condenser and evaporator coils to obtain maximum surface contact and allow good velocity for proper oil return. If oil return is not proper, compressor failure will be frequent and oil will act as an insulator to slow heat absorption. Older 1/2" standard tube coils are designed for compressors with totally different characteristics from today's units. It is not uncommon to see an older 4 ton condensing unit with a 52,000 Btu compressor where today's 4 ton unit may only have a 36,000 Btu compressor. Both units may have the same capacity, but the old system runs a 200 pound higher head pressure and 1/2 the coil surface. A smaller compressor can do the same cooling job because less of the energy goes to moving the refrigerant and more to moving heat. Because of higher head pressure, old capillary tubes were smaller and sized for between 220 and 280 pressure drop across tubes. Newer units are based on a pressure drop of 100 psi or less. Looking at these factors, it is natural to see where an old capillary would starve the evaporator coils if it was matched with a new condensing unit, unless the system was overcharged to compensate. Running the unit and charging it, a technician may not be aware he has reduced efficiency by 30%, and the customer may never get the return on the investment made.

A system without a crankcase heater or liquid line selonoid valve may also contribute to reduced efficiency. This can occur if the refrigerant system is piped such that liquid refrigerant will migrate into compressor crankcase. Liquid refrigerant will always move to a low, cool area that preferably contains oil. A crankcase heater will boil this liquid to prevent flooded starts. A liquid line selonoid valve will close off the refrigerant line when the compressor stops to prevent migration. A secondary benefit to the selonoid valve is that it can boost SEER by 0.50. This is due to the fact that it keeps a column of liquid at the metering device in "off" cycle and when the system is started, it refrigerates immediately. Flooded starts increase energy consumption during starting and eventually during running from bearing wear. The increase during starting is due to the fact that a compressor cannot compress liquid and is under great strain. The long term increase in energy consumption is because liquid refrigerant is an excellent solvent and it thins the oil which lubricates the bearing surfaces. Other effects can be broken or bent valves, stretched heat bolts and worn rings, all of which cause lower compression ratios and reduced capacity.

Dirt has long been an enemy of HVAC equipment, but it can make an even larger impact on the efficiency of modern systems. The efficiency values, or SEER ratings are given for new and clean equipment. There is nothing figured in for dust and dirt that will accumulate on condenser and evaporator coils from the second the unit is started. It is imperative for service technicians to keep the systems clean and to educate customers on the importance of monthly filter changes. In most households, electronic or good mechanical air filters such as "Space Guard" will pay for themselves by keeping evaporator coils clean.

Please indicate whether the statements below are True or False.
_____1. The high pressure efficiency units of today run higher head pressure than their older counterparts.

_____2. When changing out a condenser, it is "OK" to leave the old coils in the attic.

_____3. Improper oil return can lower efficiency and reduce compressor life.

_____4. Electronic air cleaners do nothing for system efficiency and are only a sales gimmick.

_____5. When replacing an outdoor section of an HVAC system, old refrigerant tubing should be checked for proper sizing and kinks.

_____6. ARI rates systems and calculates SEER based on 50' of tubing between indoor and outdoor units.

Answers to Activity (True / False):
1. F
2. F
3. T
4. F
5. T
6. F

Directory of Certified Unitary Air-Conditioners (Section AC), Unitary Air-Source Heat Pumps (Section HP) and Sound-Rated Outdoor Unitary Equipment. Air-Conditioning & Refrigeration Institute, Arlington, VA. 1992.

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