[Equest-users] [Bldg-sim] eQuest - Energy consumption increasing on reducing Glass U-Value

[David Eldridge]

Jim’s suggestion is a classic case for why energy would increase due to higher performance change in the envelope – my other best suggestion is to review the model outputs that restate the space loads and window performance and verify that the inputs are as intended. Side note that 2.0 to 2.5 W/sf for equipment might be a little on the higher side, depending on what the commercial spaces are and density of computers or other electronics.

I suggest also to look at electricity and/or natural gas monthly to see the pattern of the changes (or to use a report variable to see heating, cooling, and fan motor energy separate if all-electric) which may help determine if the result makes sense or if a modeling input needs to be changed.

Another thing to look at is what energy flows increased and which deceased – it could be possible if you have high airflow minimums or constant volume that there is a lot of reheat in the spaces. When the window was upgraded the amount of “freeheat” from the outside would be reduced. I don’t think this is likely from your equipment loads, but I use it as an example of examining the monthly data to determine possible causes for the net increase in energy use – if you can identify specifically what equipment used more energy it will help to debug the model.
David

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
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From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of akshay gupta via Bldg-sim
Sent: Friday, November 03, 2017 8:19 AM
To: Jim Dirkes <jim at buildingperformanceteam.com>; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] eQuest - Energy consumption increasing on reducing Glass U-Value

Hi Jim

Thanks for the reply. Actually, the project we are modelling are designed to be energy efficient commercial spaces. So for example, interior LPD is not more than 0.5 W/sqft (LED lights), EPD is around 2.0 - 2.5 W/sqft, Occupant Density is around 50 Sqft /person. So I dont see any area where internal heat gain is unusually higher where the building needs to cool itself off by conducting heat outside (inside hotter than outside).

I think there something else.

Regards

Akshay

On 3 November 2017 at 18:42, Jim Dirkes <jim at buildingperformanceteam.com<mailto:jim at buildingperformanceteam.com>> wrote:
Akshay,
While there are many things that could contribute to this situation, consider:
A smaller U value means that there is less conduction through the construction. With less conduction, a smaller cooling load will normally decrease cooling energy.

An exception to this is when internal loads are higher than normal. In that case, the building needs to get rid of internal heat (provide cooling) most of the year. When the envelope has more insulation (lower U-value), it inhibits heat removal and can increase cooling energy.

Thanks to my friend Javed Iqbal for reminding me of this recently. He is preparing a paper which discusses this phenomenon for buildings in the central European climate.


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