[Greenbuilding] One more question on AC

John Salmen terrain at shaw.ca
Tue Jul 9 15:45:02 MDT 2013

Used to have a concern with oversized pumps cycling inefficiently. Don't
know if that is still a concern with 'newer' tech


From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org]
On Behalf Of Alan Abrams
Sent: July-09-13 2:32 PM
To: Green Building
Subject: Re: [Greenbuilding] One more question on AC


on my current passive house project (pre-certified in May; permit issued
today!) I opted for separate distribution systems for ventilation and for
heating and ac.  there were too many unique conditions throughout the house
(different floor levels; different solar exposures and shading conditions;
different functions, such as cooking, bathing, laundering, etc) to rely on a
gently puff of ventilation air to heat, cool, and dehumidify--while still
exhausting stale air and bringing in fresh air in appropriate volumes
throughout a complex floor plan.  Conversely, if the ducts are sized for max
loads, then it would be optimistic to try to push properly metered
ventilation air through that system while the heat pump was not running.
Thus dual ducting.


the heating and air will be an inline Fujitsu, about 18KBtu capacity.  It's
oversized for the calculated loads, but only to push enough volume to handle
dehumidification and prevent hot spots.  One concern is overheating in
shoulder months, when the leaf cover is gone and the sun is lower than the
overhangs--which are tuned for summer shading and max winter gain--IOW's we
anticipate days where some cooling may be required in the afternoon, and
heating is required later at night.  


at a ton and a half, it raises the question of why not just go with a 2 ton
Carrier Infinity, with almost twice the fan capacity--but still able to wind
down to maybe 3KBtu.  But we decided to do a fine tuned duct system,
reducing the trunk at each tap, with sweeping takeoffs and boots, to reduce
friction where-ever possible.

this all is counter to the passive house legend--that when you hit some
sweet spot of insulation, you only need a small scale ventilation air
distribution system to distribute heat and cooling--thus justifying the
premium for the 9 inches of insulation under the slab--but I think that
dealing with our latent loads dispels that myth.


On Tue, Jul 9, 2013 at 4:55 PM, Gennaro Brooks-Church - Eco Brooklyn
<info at ecobrooklyn.com> wrote:

Combing ERV/HRV and cooling is a huge question. Does anyone have experience
with a new system where you can plan for the ductwork? In that can could you
install large ducts and run the ERV and some sort of cooler in the same
ducts? In that case I think it may be better to find some inline cooling
system instead of jerryrigging a minisplit to work inline?

Gennaro Brooks-Church
Director, Eco Brooklyn Inc.
Cell: 1 347 244 3016 USA
22 2nd St; Brooklyn, NY 11231


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