Excessive summer heating

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I received comments back from the LEED reviewers; they comment that I have excessive summer heating. Prior to submitting to USGBC, I had already fooled with the throttling range and system cooling control to warmest. Tweaking those helped with the unmet heating hours I had previously. Could messing with those 2 items before have caused the excessive summer heating? Any suggestions to lower the excessive summer heating? I've attached the inp and pd2 file. I'm running version 3.64.
Any help is appreciated. Thanks!

Amy Harmon
Mechanical Engineer
Scheeser Buckley Mayfield LLC
1540 Corporate Woods Parkway
Uniontown, OH 44685
Phone: (330) 896-4664 ext. 107
Direct: (330) 526-2707
Fax: (330) 896-9180
aharmon at sbmce.com
www.sbmce.com

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Thank you

Harmon, Amy's picture
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Joined: 2011-09-30
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Hi Amy,

The current model (you sent) has 172 unmet load hours coming from zone: "EL5 SSW Perim Zn (G.SSW2)"

I gave a real quick look at model and as per LEED it looks fine to me. DO you mean to decrease these unmet load hours or you already made changes and sent the model here at eQuest group?

I would say check SS-R report and see what zones have unmet load hours & you can increase supply CFM in those particular zones.

Best,
Harshul Singhal, LEED AP BD+C
Project Consultant
Thornton Tomasetti
386 Fore Street, Suite 401
Portland, ME 04101
T +1.207.245.6060 F +1.207.245.6061
D +1.207.245.6074
HSinghal at ThorntonTomasetti.com
www.ThorntonTomasetti.com

harshul263's picture
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Hi Harshul!
Thanks for the response, it's not the unmet heating hours I'm too concerned about it unless something I did previously has caused the summer excessive heating.
The LEED reviewers commented that report PS-A & PS-B showed an excessive amount of heating during the summer months...in the month of July the heating load of 269 MBTUs of heating roughly 20.9% of the total heating and cooling load (269 MBTU + 1018.7 MBTU).

Amy Harmon
Mechanical Engineer
Scheeser Buckley Mayfield LLC
1540 Corporate Woods Parkway
Uniontown, OH 44685
Phone: (330) 896-4664 ext. 107
Direct: (330) 526-2707
Fax: (330) 896-9180

Harmon, Amy's picture
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What type of building is it? Reheat would be expected for buildings with higher minimum airflow such as hospitals or laboratories.

The LEED Reviewer's comment might not be justified if the building is designed to use a large amount of reheat energy.

It's also possible that the comment is indirectly saying that the minimum airflow settings in the models are too high, or that the overall supply air volume is too large.

If you can provide backup that that airflow volumes are correct that would help explain heating use in the summer.

David

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Associate

Direct: (847) 316-9224 | Mobile: (773) 490-5038

Grumman/Butkus Associates | 820 Davis Street, Suite 300 | Evanston, IL 60201
Energy Efficiency Consultants and Sustainable Design Engineers

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David Eldridge's picture
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Amy,

The min-flow-ratios for your VAV zones are 1.00, meaning airflow is never reduced to those spaces. Check the "Air Flow" drop-down in the air-side zone spreadsheet, and check the Min Flow Ratio column. This explains the high amount of summer reheat.

Also, your VAV reheat coils are set to 50?F reheat delta T, which is very high.

Thanks,

Coles Jennings, PE, BEMP, LEED AP BD+C
Senior Associate
Sr. Energy Engineer, Building Sciences Studio Manager

H&A | Hankins & Anderson | www.ha-inc.com
d: (804) 521-7045 p: (804) 285-4171 f: (804) 217-8520

Coles Jennings's picture
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The building is an existing 10 story dormitory built in the 60's. It's 100% OA. The HVAC design consisted of replacing an air handler and replacing 2 pipe FCUs with 4 pipe FCUs. Architecturally, they replaced all the single pane windows with double pane windows.

Amy Harmon
Mechanical Engineer
Scheeser Buckley Mayfield LLC
1540 Corporate Woods Parkway
Uniontown, OH 44685
Phone: (330) 896-4664 ext. 107
Direct: (330) 526-2707
Fax: (330) 896-9180

Harmon, Amy's picture
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Joined: 2011-09-30
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Hi Coles!
I have a 100% OA unit. I had to increase the reheat to decrease unmet heating hours.

Amy Harmon
Mechanical Engineer
Scheeser Buckley Mayfield LLC
1540 Corporate Woods Parkway
Uniontown, OH 44685
Phone: (330) 896-4664 ext. 107
Direct: (330) 526-2707
Fax: (330) 896-9180

Harmon, Amy's picture
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Joined: 2011-09-30
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Amy,

Even though it is 100% OA, is it constant volume? The min-flow-ratio applies to total supply air for each zone, not just outside air. If min-flow-ratio is set to 1.0, then the VAV unit will never reduce its supply flow and you will certainly have a lot of summer reheat.

Thanks,

Coles Jennings, PE, BEMP, LEED AP BD+C
Senior Associate
Sr. Energy Engineer, Building Sciences Studio Manager

H&A | Hankins & Anderson | www.ha-inc.com
d: (804) 521-7045 p: (804) 285-4171 f: (804) 217-8520

Coles Jennings's picture
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Hi Amy,

If the system is a constant volume system providing 100% OA at a relatively low temperature the model may be behaving as expected, i.e. the system may be designed such that it causes significant reheat with air that is too cold for comfort (with the supply temperature limited by the needs of the warmest zone, say to 55-60?F) being delivered to the rooms. If this is the case, then I would suggest you reply to the comment with a description of the system being modelled and explain why there is excess reheat. Given that the reheat is penalizing the proposed model (i.e. costing LEED points), it probably won?t be a sticking point for the review.

That said, I?m wondering what the rationale is for modelling a 4-pipe fan coil system with 100% OA as a VAV system with a constant supply air flow rate. Is the VAV system meant to be a make-up air system supplying fresh air to the corridors? I?m thinking that in a 4-pipe fan coil system the make-up air system would typically be designed to deliver tempered air at 65-75?F with the fan coils in each zone providing additional cooling or heating as needed, in which case there should be no need for reheat. Can you try changing the cooling setpoint for the VAV systems to a maximum reset temperature of 65-70?F? Would this be in accordance with the design?

All the best,
Dan

?
Daniel Knapp, PhD, PPhys, LEED? AP O+M
danielk at arborus.ca

Arborus Consulting
Energy Strategies for the Built Environment
www.arborus.ca
76 Chamberlain Avenue
Ottawa, ON, K1S 1V9
Phone: (613) 234-7178 ext. 113
Fax: (613) 234-0740

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