Tuesday, May 22, 2012

Applied Bio-physics

I spent all last week in southern Ontario, Canada. I reported earlier that I had visited Ottawa and Montreal. This trip was to several cities in S Ontario, including Toronto. I visited 11 engineering offices and met with about 80 mechanical engineers. At each location, I asked the overhead heat question: What is ASHRAE’s recommended discharge to room differential when heating from the ceiling?” Only 7 engineers knew the answer. (15 deg F). I was not surprised. The building code in Ottawa references ASHRAE 62.1 2004. So that means that 90% of the engineers would likely violate the building code when designing a system. Looking at building schedules across the US and Canada, I’d say this was about average.

When ordering VAV boxes with heat, our reps typically have to use the box schedule to select either the number of rows, or the KW. I’d estimate that 90% of the schedules have leaving air greater than 90 deg F. I would also guess that the engineer hasn’t upped the ventilation requirement by 25% as required by ASHRAE 62.1, which is often code.

Further, a discharge greater than 15 deg F above the room means the space will no longer comply with the vertical temperature stratification limits specified in ASHRAE Standard 55 (comfort). While typically not code, one cannot get the LEED comfort point with this design.

BOMA, for the past several years, reports that the #1 reason for not renewing the lease in a high rise building is occupant dissatisfaction with the thermal environment. Looking at the typical VAV box schedule, I am not surprised.

I wrote an article for the ASHRAE Journal a few years ago which is on our web site: (http://www.krueger-hvac.com/lit/pdf/white_AJ_reheat.pdf). All the information in that 2006 article was known in 1979. The actual business we are all involved with is “applied bio-physics”. We are providing life support systems for occupied buildings, and from my experiences, we need to be doing a better job.

Authored by: Dan Int-Hout, Chief Engineer Krueger