Energy Recovery Wheel on VAV System

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Hello All,

I am trying to model an enthalpy energy recovery wheel on a VAV air handler serving multiple zones, and I cannot seem to get any exhaust air to pass through the wheel. I have specified the design exhaust loads at the Zonal Level and I have also setup the wheel control sequence using values that others on this forum have posted:

* Operation = OA Exhaust DT

o DT = 5 degree F

* Operating Mode = OA Heat/Cool

* Make up Air Temp Cntrl = Mixed Air Reset

* Capacity Control = Bypass OA
Whenever I run the model I get an error stating, "Energy Recovery ventilator: S1 Sys (VAVS) has an exhaust flow 50% of the supply flow. Performance may be compromised. OA & Exhaust: 7313. 0." The total sum of all the Zonal Exhaust Loads in 5505 CFM, and none of this is making it to the wheel. Does anyone have any insight as to what I might be doing wrong here? My end goal is to have the wheel modulate the return airflow in order to match the Outside Air CFM demand by the VAV system. Any input is greatly appreciated.

Thanks,

Miles Martschink, Jr
Mechanical Design Engineer
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mmartschink's picture
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Joined: 2016-01-06
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Zone exhaust is presumed to exhaust directly to the outside without going back to the system, i.e. it is assumed that you are specifying a separate zonal exhaust fan that is not connected to the main VAV system. If you remove the zone exhaust, the system level exhaust will be determined by the outdoor air fraction of the supply air. This outdoor air fraction will depend on the demand for outdoor air from the zones. i.e. the outdoor air is specified at the zone level, and determines the outdoor air supply at the system level.

Hope that helps,
Dan

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

Energy Efficiency Expert
Arborus Consulting
76 Chamberlain Ave
Ottawa ON K1S 1V9
(613) 234-7178
?
Daniel Knapp PhD, P Phys, LEED AP O+M
danielk at arborus.ca

Energy Efficiency Expert
Arborus Consulting
76 Chamberlain Ave
Ottawa ON K1S 1V9
(613) 234-7178

Daniel Knapp's picture
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Joined: 2011-09-30
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Sadly Daniel, I do not think this is quite correct. In the current
version of eQUEST/DOE2.2, if you add zonal exhaust the total amount of
heat recovery does not change. I agree that it should -- heat recovery
should go down as zonal exhaust is increased, but eQUEST does not
currently do this. I was quite surprised when it was pointed out to me.
A quick parametric test run where zonal exhaust is added will show that
the total heat input will not go up when it should and on the ERV report
(in the .sim) the amount of recovered heat will not change.

If however, you set the return fan volume lower than the supply fan
volume (on the fan -> flow parameters tab), then the heat recovery
capacity will be reduced appropriately.

bfountain's picture
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Joined: 2011-09-30
Reputation: 201

I?m actually wrestling with re-understanding these issues in parallel with
you, Miles.

The DOE-2 entry for EXHAUST-FLOW specifies zonal exhaust doesn?t get back
to the air handler for exposure to heat recovery equipment at the system
level (*I wish it were an option*):

This diagram illustrates my current understanding/impression of what plays
into the exhaust airflow seen for recovery:

This is however the first I?ve heard that zonal exhaust doesn?t actually
work into the balance to determine exhaust/relief exposed to energy
recovery. Some parametric tinkering is certainly in order!

My immediate thought is to wonder if the zonal EXHAUST-SOURCE (i.e. air
handler vs. infiltration) could be playing into that observation? Seems to
fit logic?

~Nick

*NICK CATON, P.E.*
*Owner*

*Caton Energy Consulting*
306 N Ferrel

Olathe, KS 66061

office: 785.410.3317

www.catonenergy.com

Nicholas Caton's picture
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Joined: 2014-12-09
Reputation: 0

Actually it?s quite confusing within DOE?s help but I think you are wrong Nick. Zonal exhaust does go throught the central heat exchanger.
Below is the extract from DOE?s volume that points this out :

[cid:image003.png at 01D15CF9.C9D5A910]

The last sentence clears it out.
? All exhaust other than exfiltration is assumed to flow throught the ERV. This includes both zonal and central exhaust. ?

[cid:image004.jpg at 01D15CF9.C9D5A910]

Patrick Lapierre_ing.
plapierre at bpa.ca

De : Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] De la part de Nicholas Caton
Envoy? : 1 f?vrier 2016 13:51
? : Daniel Knapp ; Miles H. Martschink ; bfountain at greensim.com
Cc : equest-users at lists.onebuilding.org
Objet : Re: [Equest-users] Energy Recovery Wheel on VAV System

I?m actually wrestling with re-understanding these issues in parallel with you, Miles.

The DOE-2 entry for EXHAUST-FLOW specifies zonal exhaust doesn?t get back to the air handler for exposure to heat recovery equipment at the system level (I wish it were an option):
[cid:image005.png at 01D15CF9.C9D5A910]

This diagram illustrates my current understanding/impression of what plays into the exhaust airflow seen for recovery:
[cid:image006.png at 01D15CF9.C9D5A910]

This is however the first I?ve heard that zonal exhaust doesn?t actually work into the balance to determine exhaust/relief exposed to energy recovery. Some parametric tinkering is certainly in order!

My immediate thought is to wonder if the zonal EXHAUST-SOURCE (i.e. air handler vs. infiltration) could be playing into that observation? Seems to fit logic?

~Nick

NICK CATON, P.E.
Owner

Caton Energy Consulting
306 N Ferrel
Olathe, KS 66061
office: 785.410.3317
www.catonenergy.com

Patrick Lapierre's picture
Joined: 2015-01-28
Reputation: 0