HVAC sizing - triple vs. dual

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eQuest is showing for identical bldgs HVAC sizing for triple pane to be
more than that for dual pane for cold climates like Edmonton. Is that
normal?

Namrata

Namrata Vora's picture
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I am assumung this is cooling load and not heating?

It really depends on your building type. An internally driven building with lots of solar heat gain and lights and equipment might actually show that - especially in a cooler climate where you could get some conductive heat loss through the skin.

Its unusual, but possible.

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Sami, Vikram's picture
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For design flow (cfm), cooling (tons) & heating ((BTuh/sf).

The bldg type is a 20story commercial bldg.

Namrata

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What DOE2 report are you basing the sizing on?

Haynes, Glenn's picture
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Hi Namrata,

As I see it, there are 2 ways that glass affects energy: solar gains coming in (which is tied to the SHGC) and heat transfer through the unit (tied to the U-factor). If you substantially reduce the SHGC going from double to triple pane, then you may be losing some passive heating, thus increasing your boiler sizing (although I would expect it would have to be a substantial change in SHGC to outweigh the benefits of improved U-factor). As for U-factor: in a building with high-internal loads you may benefit in summer from excess heat being released through the glazing (as Vikram pointed out) - so this would increase your peak chiller capacity. That would not entirely surprise me, but I think an increase in boiler size is less typical.

My 2?.

Cheers,
Alex Krickx

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During the summer peak wouldn't you expect the heat flow to be into the spaces from the outside? You have been talking about times when the outside temperature is below the space set points for the free cooling effect.

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Glenn - you're right. Low U-factors can add to annual heating loads when the temperature outside is cooler than inside. But that shouldn't affect peak loads, because the outside temp > inside temp. Which makes it even more confusing why chiller peaks increase, unless SHGC drastically increased (but then that would mean boiler peak decreases because of passive heating). Sorry for the mix-up.

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The effect of SHGC on heating energy use is very significant in cold,
sunnier climates like Edmonton. Whether triple pane results in
better overall energy consumption compared with double pane depends
on the U-value improvement and the change in SHGC. I have witnessed
the skepticism in many Architects reactions when you tell them that
their super glazing system - designed for cooling climates, ends up
using more energy than a less expensive glazing.

Chris Jones

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