Unmet Heating Hours - ES

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All,

I am modeling a two-story elementary school with a VRV / DOAS system in
one area (classrooms, admin.), and a VAV system in another (gym,
cafeteria, food prep.). The unmet heating hours are currently around
750, and I am at my wit's end to reduce them further. I have
incorporated suggestions such as increasing the throttling range
(currently at 6, helped a little bit) and sizing ratio (currently at
1.15, although increasing to 2.00 did not help much). As I have also
tried my best to model the VRV / DOAS system, I'm still not sure if it
is correct... I've just picked up what I could from the users archives.

Does anyone have suggestions for reducing the unmet heating hours that I
may not be aware of? I have attached the .inp file. Can anyone see
glaring mistakes in the model?

Thanks,

Chris Swanson

Chris Swanson's picture
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Joined: 2011-09-30
Reputation: 0

Make sure that your thermostat type is appropriate. Use Reverse Action if you want to allow the supply flow in heating mode to rise above the minimum flow ratio, otherwise use Proportional. Also try reducing the cool control range from 4 deg to 1 deg.

Kelsey Van Tassel

Kelsey VanTassel's picture
Joined: 2011-09-30
Reputation: 0

It sounds like the heated air is not being allowed to go where there is a
call for conditioning, have you checked your system reports too? it might
have to do with your system & temp scheduling. Can you send your .pd2 &
.inp file both so that we can open your file in eQuest?

thanks,
pkg

Pasha Korber-Gonzalez's picture
Joined: 2011-09-30
Reputation: 400

Attached are both the .pd2 & .inp files. I will look into the
suggestions below in the meantime.

Chris Swanson

Chris Swanson's picture
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Chris,

Your building has 14 underheated zones.

Go to "Tools", "Quality Control Reporting...", then click the "QC
Details" tab, and then select "Show Errors Only".

Check section 6: Zone Control and Equipment Sizing.

What I usually do is that I increase the supply flow rate for each of
these 14 zones. This is the best option to solve the issue of unmet
loads in my opinion.

Best,

Omar

Omar Katanani's picture
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I agree with Omar, especially if you let eQUEST autosize your cfm/sf. It
sets it a .5 cfm/sf which in my experience is almost always too low.

Carol

cmg750's picture
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Joined: 2010-10-05
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Omar,

Your suggestion seems to have done the trick! I did not know about the
Quality Control Reporting Tool, and now I realize how much of an asset
it will be in the future.

Thanks a lot

Chris Swanson

Chris Swanson's picture
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Joined: 2011-09-30
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No problem, it's the first time I actually have a valuable answer!

However, note that I couldn't justify some of my zones with excessive
underheating or undercooling. I do not know why these specific zones
have caused problems. Keep in mind that you need to coordinate with the
Mechanical Engineers regarding any changes in the supply flow rates. I
had to increase the supply flow rate of a gym from 11,000CFM to
16,000CFM in eQUEST, and this made absolutely no sense to the design
team!

Best,

Omar

Omar Katanani's picture
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Joined: 2011-09-30
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Yay, Omar!! You are really learning this stuff fast. It makes sense to me
that a gym would need more airflow. It probably should be thought of in the
terms of air changes per hour (ACH) instead of cfm/sf, due to the volume of
a gym being greater than a normal space. I'm surprised this made no sense to
the design team. Pretty soon you'll be teaching them all kinds of valuable
lessons!

Cheers,

Carol

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