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<font face="Helvetica, Arial, sans-serif">There is a burgeoning area
of research that is trying hard to solve the dehumidification
problems in high performance buildings. We have done literally
dozens of forensic investigations in energy efficient buildings
because of a lack of humidity control.<br>
Almost all air conditioning systems have a sensible heat ratio of
about 0.70 to 0.75. This means that 3/4 of the energy goes into
cooling the air and 1/4 goes into removing moisture.<br>
In Philly or New York, if you control solar gain (shade) and have
decent insulation and airtightness, the ratio required is more
along the lines of 0.30 to 0.60. So, normal systems cause
problems with high humidity. ASHRAE has spent a ton of money in
the last while on research to try and identify and solve this
problem.<br>
<br>
In weather that is dry enough (eg lets say that air would have
less moisture in it than it would at 75F and say 40%RH) it is so
cool outside that night ventilation works (eg this occurs on
nights when the temp drops below 50F). This is Gennaro's New
Mexico example. Works great.<br>
Does not work in NYC, Philly, even Chicago. In Washington DC it
is hopeless.<br>
<br>
<br>
</font>
<div class="moz-signature">Dr John Straube, P.Eng. <br>
<a class="moz-txt-link-abbreviated" href="http://www.BuildingScience.com">www.BuildingScience.com</a></div>
<br>
On 12-06-08 2:21 PM, Gennaro Brooks-Church - Eco Brooklyn wrote:
<blockquote
cite="mid:CAPV9BxMsJMUZ2soX8E7hL=eu39yHofYHGkT1tK8iAHVScfeTOA@mail.gmail.com"
type="cite">In NY at least, when it is hot, it's humid.
Night ventilation, like fans, work in lower hot temperatures here
but when it gets really hot it stops working comfort wise. You're
just stirring the soup at that point.
<div>
Some days the AC is almost needed more for
its humidification than for its cooling.</div>
<div><br clear="all">
Gennaro Brooks-Church<br>
Director, Eco Brooklyn Inc.<br>
Cell: 1 347 244 3016 USA<br>
<a moz-do-not-send="true" href="http://www.EcoBrooklyn.com"
target="_blank">www.EcoBrooklyn.com</a><br>
22 2nd St; Brooklyn, NY 11231<br>
<br>
<br>
<br>
<div class="gmail_quote">On Fri, Jun 8, 2012 at 1:25 PM, nick
pine <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:nick@early.com" target="_blank">nick@early.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
John Straube writes:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
... consider the humidity. At night, since it cools down,
the RH rises. Flooding a house with 68F/80-90%RH air loads
the house up with vapor in all the drywall, wood,
furnishings. The next morning even if the temperature
stays low (say 76 or 78) the RH in the house will be
uncomfortably high. If you have more mass (lots of exposed
concrete ceilings for example) the concrete stays cool
enough that you can get condensation on the ceiling. I
have seen this happen in old masonry warehouses .<br>
</blockquote>
<br>
To me, smart ventilation considers absolute humidity, with
ventilation only on cool dry nights when the result would be
comfortable. Flooding a house with dry air can store dryness
in the same way that thermal mass can store coolth. Concrete
absorbs 1% of its weight by moisture as the RH rises from 40
to 60%.
<div class="HOEnZb">
<div class="h5"><br>
<br>
Nick <br>
<br>
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