Dual Duct with package Cooling

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A friend of mine asked me about such a system. I looked it up, and lo and behold, eQuest doesn't this as a system.
Is there any equivalent system that can dynamically mimic this?
Thanks,
John R. Aulbach, PE

John Aulbach's picture
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Joined: 2011-09-30
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Hi John

If by packaged Cooing you mean Air Cooled DX then, how about trying:

* Dual Duct system w. CHW
* ?Chiller? = Air cooled with appropriate compressor type (recip or scroll) and count
* Pump power = 0
* CHW supply temperature = ~ DX evaporator T

Good luck

Melissa Crowe, BEMP, LEED AP
Sr Mechanical/Energy Engineer
[cid:image001.png at 01D8800A.7D8FBD30]
161 Worcester Road, Suite 305
Framingham, MA 01701
O: 508.647.9200
C: 978-204-2559
cmta.com
[cid:image002.png at 01D8800A.7D8FBD30][cid:image003.png at 01D8800A.7D8FBD30][cid:image004.png at 01D8800A.7D8FBD30]

Melissa
Melissa Page Crowe's picture
Joined: 2011-09-30
Reputation: 1

Does it let you pick DX for the multizone AHU type?

David

David S. Eldridge, Jr., P.E., BEMP, BEAP, HBDP, GGF/A
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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No.
Melissa

Melissa Crowe, BEMP, LEED AP
Sr Mechanical/Energy Engineer
[cid:image001.png at 01D88011.31C17130]
161 Worcester Road, Suite 305
Framingham, MA 01701
O: 508.647.9200
C: 978-204-2559
cmta.com
[cid:image002.png at 01D88011.31C17130][cid:image003.png at 01D88011.31C17130][cid:image004.png at 01D88011.31C17130]

Melissa
Melissa Page Crowe's picture
Joined: 2011-09-30
Reputation: 1

I replied too fast the multi zone is only DX will not allow CHW.

However this is not thermally equivalent to Dual Duct where you can cool one zone while heating the other with out reheating.

Melissa Crowe, BEMP, LEED AP
Sr Mechanical/Energy Engineer
[cid:image001.png at 01D88012.34DD13A0]
161 Worcester Road, Suite 305
Framingham, MA 01701
O: 508.647.9200
C: 978-204-2559
cmta.com
[cid:image002.png at 01D88012.34DD13A0][cid:image003.png at 01D88012.34DD13A0][cid:image004.png at 01D88012.34DD13A0]

Melissa
Melissa Page Crowe's picture
Joined: 2011-09-30
Reputation: 1

Thank you. Melissa, I think you hit the nail on the head. I am AMAZED that eQuest cannot formally do DX dual duct. Those systems certainly DO exist. Just never noticed the omission before in the program.

On Tuesday, June 14, 2022, 02:14:35 PM PDT, Melissa Crowe wrote:

I replied too fast the multi zone is only DX will not allow CHW.

?

However this is not thermally equivalent to Dual Duct where you can cool one zone while heating the other with out reheating.

?

?

Melissa Crowe, BEMP, LEED AP

Sr Mechanical/Energy Engineer

161 Worcester Road, Suite 305

Framingham, MA 01701

O: 508.647.9200

C: 978-204-2559

cmta.com

?

?

John Aulbach's picture
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Joined: 2011-09-30
Reputation: 1

John

It often seems that reality was not the prime mover in the design of eQuest.

I could name several other system types that have similar limitations.

Maybe it would not be interesting if we didn't have to come up with cleaver work arounds.

Regards

Melissa Crowe, BEMP, LEED AP
Sr Mechanical/Energy Engineer
[cid:image001.png at 01D88014.B035B280]
161 Worcester Road, Suite 305
Framingham, MA 01701
O: 508.647.9200
C: 978-204-2559
cmta.com
[cid:image002.png at 01D88014.B035B280][cid:image003.png at 01D88014.B035B280][cid:image004.png at 01D88014.B035B280]

Melissa
Melissa Page Crowe's picture
Joined: 2011-09-30
Reputation: 1

It is - this is a multizone system with hot deck and cold deck where it blends the two airflows to satisfy the zones, taking constant flow overall with proportion of cold and hot deck air. The mixing takes place at the AHU though and a single duct goes out to the zone as opposed to the dual-duct approach. The size of the units is limited since there isn't enough room for ductwork branches, I've usually seen these from three to seven zones. So in that regard it makes sense for a DX although I've mostly seen these in university buildings which do have CHW and HW or steam, sometimes at hotels.

For the dual-duct AHU where the mixing takes place at the zone, you can have a much higher number of zones since the space isn't constrained at the discharge air location so I can see that DD AHUs I've seen would be very large and tend to be CHW and HW/Steam and not DX.

So I think it's probably the best approximation to use the multizone template.

The chiller idea would give another approach but could have part load performance different than the DX system would have, but also a way to attempt a workaround.

David

David S. Eldridge, Jr., P.E., BEMP, BEAP, HBDP, GGF/A
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

grummanbutkus.com | Facebook | Twitter | LinkedIn

David Eldridge's picture
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Joined: 2012-05-08
Reputation: 1

I have learned something. Thank you. I have actually never had to model a system like that but you are correct, I have looked at them all but misunderstood the Multizone. I see there are actually several dual duct systems. Packaged Multi zone is DX, Multizone is CHW and then there is Dual Duct CHW.

Say something ignorant...learn something new.

Melissa Crowe, BEMP, LEED AP
Sr Mechanical/Energy Engineer
[cid:image001.png at 01D8809B.BE2FF5D0]
161 Worcester Road, Suite 305
Framingham, MA 01701
O: 508.647.9200
C: 978-204-2559
cmta.com
[cid:image002.png at 01D8809B.BE2FF5D0][cid:image003.png at 01D8809B.BE2FF5D0][cid:image004.png at 01D8809B.BE2FF5D0]

Melissa
Melissa Page Crowe's picture
Joined: 2011-09-30
Reputation: 1

For those reading but still wondering what we're talking about, here are some system descriptions and schematics from this application guide from York.
Multizone Application of Solution Units (johnsoncontrols.com)

As infrequently as we see multizone units still running, an even smaller group of them need to be modeled in a whole building modeling program so it's getting kind of rare to model one. Most of these are smaller and would be replaced without a modeling effort.

There are a few of the larger DD systems still out there as deep retrofit candidates so maybe more likely to be modeled. I've got my eye on one in particular.

David

David S. Eldridge, Jr., P.E., BEMP, BEAP, HBDP, GGF/A
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

grummanbutkus.com | Facebook | Twitter | LinkedIn

David Eldridge's picture
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