How do I, as a Home Energy Rater, enforce the requirement that a Manual J Sizing Calculation be performed for an ENERGY STAR rated house?
The requirement reads:
All cooling equipment, regardless of whether it is used to satisfy the ENERGY STAR products requirement, must be sized according to the latest editions of ACCA Manuals J and S, ASHRAE 2001 Handbook of Fundamentals, or an equivalent computation procedure. Maximum oversizing limit for air conditioners and heat pumps is 15% (with the exception of heat pumps in Climate Zones 5 – 8, where the maximum oversizing limit is 25%). This can be accomplished either by the rater performing the calculations or reviewing documentation provided by the professional contractor or engineer who calculated the sizing (e.g., HVAC contractor). The following operating conditions shall be used in the sizing calculations and verified where reviewed by the rater:
Outdoor temperatures shall be the 99.0% design temperatures as published in the ASHRAE Handbook of Fundamentals for the home’s location or most representative city for which design temperature data are available. Note that a higher outdoor air design temperature may be used if it represents prevailing local practice by the HVAC industry and reflects extreme climate conditions that can be documented with recorded weather data; Indoor temperatures shall be 750 F for cooling; Infiltration rate shall be selected as “tight”, or the equivalent term.
In specifying equipment, the next available size may be used. In addition, indoor and outdoor coils shall be matched in accordance with ARI standards.
Note that the requirement is on cooling equipment only and that both Manual J and S must be used. Manual J is used to perform load calculations and Manual S is used to properly size the equipment.
The best thing to do is to inform your builder and his/her HVAC contractor as early in the process as possible of this requirement and to give them the actual wording. Do this in writing and keep a copy in your project file. You should receive a copy of the calculations and documentation prior to your pre-drywall, thermal bypass inspection. The furnace is usually set by this time, which means the coil is already installed. If you don’t have the documentation at this point, ask for it and stress that this is an important requirement that will cause the project to fail if not met.
The reports provided should be compared against the requirements above (make sure the operating conditions are followed, rather than the defaults being used) and the results should be compared against the actual equipment ordered for the job. If you are not familiar with the reports provided by the HVAC contractor, schedule a meeting to sit down and go through the report and input documentation. The HVAC contractor should be able to point out to you where he/she followed the required inputs and how the ordered equipment matches the load and sizing calculated by the process. Don’t forget to pull up the condenser, coil and furnace in the ARI directory to make sure a matched set is being installed as that is also part of the requirement.
If any of this is not correct, the project will not qualify for the ENERGY STAR program. You want to give your builder a heads-up about any problems as early as possible so they can be rectified quickly and with as little expense as possible. It is much easier and cheaper to fix any issues along these lines early in the project than waiting until the end.
