[Greenbuilding] One more question on AC

Alan Abrams alan at abramsdesignbuild.com
Tue Jul 9 16:14:06 MDT 2013


Gennaro--let's hold the party til after the blower door test ;^)

On Tue, Jul 9, 2013 at 5:37 PM, Gennaro Brooks-Church - Eco Brooklyn <
info at ecobrooklyn.com> wrote:

> Congrats on the PH job Alan!
>
>
> Gennaro Brooks-Church
> Director, Eco Brooklyn Inc.
> Cell: 1 347 244 3016 USA
> www.EcoBrooklyn.com
> 22 2nd St; Brooklyn, NY 11231
>
>
> On Tue, Jul 9, 2013 at 5:31 PM, Alan Abrams <alan at abramsdesignbuild.com>wrote:
>
>> 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.
>>
>> -AA
>>
>>
>>
>> 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
>>> www.EcoBrooklyn.com
>>> 22 2nd St; Brooklyn, NY 11231
>>>
>>>
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>
>
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-- 
Alan Abrams*
**certified professional building designer, AIBD
certified passive house consultant, PHIUS*
*certified passive house builder, PHIUS**
*Abrams Design Build LLC
*sustainable design for intentional living*
cell     202-437-8583
alan at abramsdesignbuild.com
www.abramsdesignbuild.com
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