[Bldg-sim] Ignore thermal mass and transients for Supply rate calculations?

[Chris Yates]

Hi James,
In my experience most CAV systems only supply outdoor air, but these 
calcs are to be applied to all conditioning air flowrates. So whether 
it's VAV (which is fairly uncommon in the UK) or Four Pipe Fan Coil 
systems they all need to use this method.
Thanks for your comments
Chris

On 12/02/2011 15:19, James V Dirkes II, PE wrote:
>
> Dear Chris,
>
> Ignoring thermal mass sounds at best ignorant and at worst 
> irresponsible.  Standard load calculations practice from ASHRAE 
> includes thermal mass always.  I suspect the CIBSE equivalent does also.
>
> Undiversified airflows, on the other hand, are the norm and 
> appropriate for constant volume systems.  Not so for VAV!
>
> *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 *Chris Yates
> *Sent:* Saturday, February 12, 2011 6:44 AM
> *To:* bldg-sim at lists.onebuilding.org
> *Subject:* [Bldg-sim] Ignore thermal mass and transients for Supply 
> rate calculations?
>
> Dear All
>
> Within the past year I've experienced at least two consultants who 
> have mandated /calculations /of Supply/ Space conditioning air rates 
> in a way that effectively ignores thermal mass and treats all loads 
> (including peak solar gain) as undiversified (i.e. permenantly on).
>
> One of the consultants has presented this as a basis for 8760 hour 
> energy models for a extensive range of building types. Fans are 
> required to operate at the /calculated /rate for all periods of HVAC 
> operation. I feel this could grossly over estimate fan power in all 
> but a few circumstances.
>
> Does anybody here model like this?
>
> Best regards
>
> -- 
>
> Chris Yates C Eng MCIBSE
>
> /Building Physics Consultant/
>
> Tel:   +447960731576
>
> Email: chris.malcolm.yates at gmail.com 
> <mailto:chris.malcolm.yates at gmail.com>
>
> Skype: christopher.m.yates
>

-- 

Chris Yates C Eng MCIBSE

/Building Physics Consultant/

Tel:+447960731576

Email: chris.malcolm.yates at gmail.com

Skype: christopher.m.yates

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