[Bldg-sim] sizing for baseline case acc to App. G

James V Dirkes II, PE jvd2pe at tds.net
Wed Jun 23 16:15:58 PDT 2010

Dear Vinay,


I'm not sure of the rationale for the ASHRAE 90.1 oversizing requirements,
however here are my thoughts:

.         I think the principal engineering rationale for oversizing is to
allow a building to reach its setpoint temperature quickly after a period of
inactivity.  As an example, if a building is inactive during a holiday and
the temperature is allowed to float several degrees lower (in winter), the
additional 25% heating capacity will enable faster return to the normal
setpoint temperature.  Steam heating systems can need even more capacity for
proper warmup capacity.

.         Oversizing is also a common practice as a "safety factor".  Most
load calculation software even has a separate input for adding this "safety




The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653


From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Vinay
Sent: Wednesday, June 23, 2010 10:00 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] sizing for baseline case acc to App. G


Hello All,

Just to clarify a point - 

What does the oversizing of capacities by 15% for cooling and 25% for
heating exactly mean? Do we only size the cooling and heating capacity or
also increase the airflow rate corresponding to the oversizing?

Thank you.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20100623/4a0f905c/attachment-0001.htm>

More information about the Bldg-sim mailing list