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GBlist: Re: ideal mass/SF Glazing/solar gain ratio for Earthships


In general, I would agree that more mass is better thermally--ignoring cost
factors.  I reduced interior temperture swings and allows for cloudy day
storage and high solar fractions.

As I mentioned in my last post, the only downsides that I see to very high
mass are (with a bit more detail than last time):

1) Mass is acoustically reflective, thus very high mass buildings usually
are also acoustically live with long reverberation times because of the
inability to use significant amounts of absorptive materials.  For some
uses, such as most residential activities, this is no problem, for others,
such as say, a classroom where speech recognition is important, too little
acoustic absorption is a big problem.

2)  Very high mass means small temperature fluctuations in the space
(usually good) beacause of high thermal capacity.  This also means that
when heating or cooling is needed, the building's response time to user
discomfort can be excessively long, since the large thermal mass also has a
very long thermal lag time.  All the mass has to be raised in temperature
for the air temperature to also rise.  Its the same control problem
encountered with a radiant floor, only a lot worse. It can be controlled,
but because the thermal information feedback is delayed in the mass
temperature--sensing--furnace control--heat supply--air temperature cycle,
some intelligent programmed control system must be used to avoid constant



>We insulate as well as use mass.  On the front-face, we use insulated
>shades to reduce heat loss in the evening.
>How can too much mass be a negative thing?
>Dr. Colin at Cranfield University in England is working in the department
>of Applied Energy and has been involved in a study regarding thermal
>analysis of Earthships.
>Jonah Reynolds
>Earthship Global Operations
>"Get an Earthship and Survive"

Mark DeKay
Assistant Professor of Architecture
School of Architecture
Washington University
One Brookings Drive
campus box 1079
St. Louis, MO 63130  USA

Office: 201 Givens Hall
314.935.6282,  314.935.8520 (fax)

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