Properly sizing and selecting HVAC equipment account for heat loss/gain throughout the year based on factors such as a building's geographic location, orientation of windows and doors, envelope tightness, outdoor air ventilation, duct leakage, and lights and appliances allows an HVAC contractor to provide a system that can properly meet design and efficiency goals.
Size and select all HVAC equipment in accordance with the Air Conditioning Contractors of America (ACCA) Manuals J and S. Load calculation must coordinate with accurate construction specifications and plans for the project as well as as-built conditions.
Complete load calculation with accredited ACCA Manual J 8th Edition Full Residential Load Calculation software. Reference ACCA for a list of approved software.
Load calculation must be stamped by a Professional Engineer along with a signed “Professional Engineer Load Calculation Affidavit”.
The following criteria should be met for all equipment sizing:
- Based on actual house orientation
- Load calculation must be based on actual home orientation as constructed
- Use most current ASHRAE Handbook of Fundamentals Climate Design Information for outdoor design temperatures
- Design heating and cooling systems using the annual outdoor design conditions as defined in the most current ASHRAE Handbook of Fundamentals
- The 99% design conditions must be used to size heating equipment
- The 1% design conditions must be used to size cooling equipment
The abridged edition of ACCA Manual J is not an acceptable methodology within the EarthCraft program.
Multispeed or multistage equipment may have OEM nominal size increments of one ton. Therefore, the use of multispeed or multistage equipment can provide extra flexibility to meet the equipment sizing requirements. The equipment oversizing limit shall be based on the largest capacity of the unit.
Floor area must be calculated using RESNET standards for conditioned floor area
Equipment sizing selection:
If the load calculation specifies a total sensible load of 36,000 Btuh, the 115% oversizing limit allows for using up to 41,400 Btuh: 36,000 x 1.15 = 41,400 Btuh
If Manufacturer X makes a nominal 3 ton AC unit and a nominal 4 ton AC unit, but no sizes in between, then Builder Y may install the 4 ton unit made by Manufacturer X as long the nominal 3 ton unit has insufficient capacity (i.e. total capacity of 36,000 x 0.95 = 34,200 Btuh). Alternately, if Builder Y wanted to use a heat pump from Manufacturer Z and Manufacturer Z offers nominal 3 ton (33,000 Btuh), 3.5 ton (39,400 Btuh) and 4 ton heat pump (45,800 Btuh), then Builder Y must install the nominal 3.5 ton unit by Manufacturer Z because the unit is between the Manual J specification and the climate zone 3, 115% oversizing limit set Manual S.
- Air Conditioning Contractors of America, see here.
- To download the Professional Engineer Load Calculation Affidavit, see here.
The EarthCraft Builder shall notify their HVAC contractor of the requirements for meeting Manual J and S requirements. The Technical Advisor will review the load calculations for accuracy and completeness at mid-construction review.
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