Increased Energy for Cooling with Increasing Insulation and Decreasing Infiltration

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Hello all,

I am a relatively new eQuest user and am encountering some non-intuitive
results.

If I make an eQuest model for a default building using just the default
values for everything, and then use the Energy Efficiency Measurement
Wizard to increase the insulation (roof or wall) or decrease the
infiltration, I see the annual energy used for heating decrease in both
cases (which I would expect), and the cooling energy increase in both cases
(which I wouldn't expect). I've tried this for two of the default building
types (Two story office building and Mutifamily low rise) and two different
climates (LA and NYC), and get the same results. I've also seen the same
behavior in other building models that I've created that differ in many
respects to these default cases.

Can someone please explain how this is possible?

Dan

dawright999's picture
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Joined: 2011-07-22
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I have seen similar in Energy Plus and was surprised at first, but came to
realize insulation does a good job at heating, as does reduction of
infiltration, but for cooling insulating above code and a tight building
can trap heat.
Question, does your model have large internal gain> if so this would
explain it..

*Jeremiah D. Crossett*

CleanTech Analytics's picture
Joined: 2012-02-09
Reputation: -1

Hi Dan,

This is a common result. You may want to search the archives, as this has
been discussed in depth before.

Many buildings, particularly non-residential buildings, are 'internal loads
dominant' rather than 'envelope dominant'. This means that the majority of
the cooling energy is spent removing heat from lighting, plug loads, people
and perhaps solar gains. None of these things are dependent on outside
temperature. So in an internal loads dominant building, there can be many
hours out of the year in which the building is in cooling mode while the
outside temperature is lower than the inside temperature. During these
hours, heat transfer through the walls (from inside to outside) and
infiltration are beneficial from a cooling standpoint. They act as a sort
of uncontrolled economizer, reducing the amount of cooling required by the
mechanical system. Increasing insulation reduces this beneficial effect.

I hope this helps,

Christian

Christian Kaltreider's picture
Joined: 2011-09-30
Reputation: 1

I agree with both, Jeremiah and Christian. In my IES experience, I
hhave had the same results by increasing insulation in exterior walls and
roof, without any changes on internal gains. And my conclusion was, while
increasing insulation, heat from internal gains cant "escape through the
walls", so cooling equipment have to do his job whatever is happening
outiside with dry bulb temperature.

Hope this helps.
*

Cristian Jara Toro*

Cristian Salvador Jara Toro's picture
Joined: 2012-05-03
Reputation: 0