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To properly design a complete HVAC system, there are three fundamental procedures that should always be followed:
*(ACCA) Air Conditioning Contractors of America
ACCA's Manual J is the first step in the design process of a new heating and air conditioning system. By following the Manual J methodology, HVAC designers are able to accurately determine the total amount of heat that is lost through the exterior of a home during the cooler months, and the total amount of heat that is gained through the exterior of a home during the warmer months. Through a complex series of calculations and inputs, the HVAC designer is able to analyze all aspects of the thermal characteristics of every wall, floor, ceiling, door and window. In addition, an HVAC load calculation also takes into consideration other factors such as the home's geographic location, orientation to the sun, envelope tightness, duct leakage, lights and appliances. ACCA's Manual J even calculates the amount of heat and humidity that each occupant of the house will add to the interior of the home.
There are two types of Manual J load calculations:
*According to the International Code Council (ICC), “Heating and cooling equipment shall be sized based on building loads calculated in accordance with ACCA Manual J”.
Once a Manual J load calculation has been completed, the HVAC designer will have the information required to accurately select the proper HVAC equipment. The equipment selection is based on performance criteria such as the equipment's total capacity to remove heat and moisture from the air as well as how much total air, and at what pressure, the system can produce. This is important to note because one manufacturer's 3 ton HVAC system can perform significantly different than another manufacturer's 3 ton system. In addition, a 3 ton system that is installed in Maryland is going to perform differently than the identical 3 ton system would perform if it was installed in Houston.
Manual D is the ACCA method used to determine the overall duct lay-out including the individual duct sizes. To design a duct system, the HVAC system designer must have completed a Room-by-Room Manual J load calculation as well as a Manual S equipment selection. All to often, duct systems are created using rule-of-thumb methods in lieu of using Manual J, Manual S and Manual D. This practice is the predominant reason for complaints of temperature differentials throughout a home as well as complaints of excessive noise caused by air velocity that exceeds the maximum allowed by Manual D.
Most states require that energy code compliance of a residential construction project must be reported in order to qualify for the appropriate construction permits. In addition, most state energy codes require that an ACCA Manual J heat load calculation be performed on the construction project, and that the heating and cooling equipment must be sized per ACCA Manual S.
While energy codes vary from state to state, in general there are 2 different paths that can be followed to determine if a construction project meets your state’s energy codes.
ConsultAir can provide you with the energy code compliance certificates and reports, also known as energy sheets, that may be required to qualify for your next building permit.
A properly designed gas piping system will insure that the system will provide sufficient gas to meet the maximum demand of the gas equipment and that it will supply enough fuel for all appliances to operate at the same time.
When designing a gas piping system, one must consider:
Gas piping systems are designed based on the gas pressure at the point of delivery (gas meter).
The three most common pressures that are used in residential gas piping systems are:
Propane (LP Gas) is also used in residential gas piping systems. Propane is typically supplied to residential buildings at 11–13 inches of water column. For 2 PSI propane elevated pressure piping systems, use a line gas pressure regulator that is set for 11 inches water column outlet pressure.
PRESSURE CONVERSION CHART
1/4 PSI = 7" w.c. = 4 oz.
1/2 PSI = 14" w.c. = 8 oz.
1 PSI = 28" w.c. = 16 oz.
2 PSI = 56" w.c. = 32 oz.
Hybrid Gas Piping Systems
Flexible gas pipe and rigid black pipe (galvanized pipe if near the coast) combinations.
It is often advantageous to use both corrugated stainless steel tubing (flexible gas pipe) and rigid pipe in the same system when elevated gas pressure is available. Using this type of system can often give you a distinct advantage over your competition. For more information, contact ConsultAir.
The information provided above is not related to any specific gas appliance. Always follow the manufacturer's installation instructions when installing gas piping and or gas appliances.
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Director of Operations
NWP Mechanical Services & Northwest Plumbing
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