Wrightsoft load short form

Discussion in 'General Discussions' started by Trever B, Dec 23, 2010.

  1. Trever B

    Trever B New Member

    I am reviewing the load calculations provided to me by my HVAC contractor for our new house. The Wrightsoft Load Short Form has each room listed with area, Htg load Clg load etc. At the bottom of the form the values are totaled and label "Entire House". Under the Clg load my value is 19,981. The next line is labled "Other equip loads" with a vaule of 1,553. Both of which I understand. The next is what confuses me "Equip @ 0.97 RSM" 20,887. What does RSM stand for? The last line is Latent cooling 3,079. The TOTAL is listed as 23,966, which is the RSM value added to the Latent load.

    I am a 17 yr veteran of commercial HVAC design at an Architectural/Engineering Firm and no one in the engineering office can figure this out, including myself. I use the Carrier HAP software for commercial installations and am unfamilar with this software. My HVAC contractor could not explain this. Can anyone here enlighten me? I am curious.

    Merry Christmas
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I Googled "Wrightsoft RSM"

    I first tried the Wrightsoft support site - no joy

    A Google search returned a 391 page pdf - the Wrightsoft users manual

    In the glossary was this:

    Rate-swing multiplier (RSM) – A correction factor used to modify sensible cooling loads to account for the effects of room temperature swing and equipment rating conditions.

    A further search of the pdf revealed no other occurrences of the phrase.

    I'd never heard of it before - Google knows everything, and it'll tell you if you ask well
  3. GCI

    GCI Member

    My understanding is that air source equipment is rated based on a 95 degree OAT (based on AHRI). The rating multiplier accounts for when the outdoor design conditions are different.

    To turn the adjustment on/off in Wrightsoft, go to Options-->Adjust for ARI Standard Rating (when unchecked, the adjustment is turned off).
  4. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Interesting...if you have specified an outdoor design temp different from the AHRI-standard 95, it does a capacity adjustment on the load calculation. I take that as an attempt to apply ACCA Manual S to load calculations. That's good, at least for air source equipment. It could add confusion in the case of geo systems.

    For air-source heat pumps, a ton of cooling in Tucson falls way short of a ton in Boston, but geo doesn't give a whit what the OAT happens to be.

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