[Equest-users] Energy Recovery Wheel on VAV System - zonal exhaust?
Bishop, Bill via Equest-users
equest-users at lists.onebuilding.org
Fri Mar 17 10:09:01 PDT 2017
I am modeling a laboratory air handler system with 100% OA, ERV at the air handler and a separate laboratory exhaust fan. I modeled the laboratory exhaust fan as zonal exhaust and thought I would only get energy recovery from the remaining exhaust at the air handler but this is not the case, as described previously below and as I confirmed using a custom hourly report.
How then to model energy recovery only for the central exhaust and not the zonal exhaust?
The one thing that comes to mind is to derate the design ERV effectiveness based on the % exhaust that returns to the ERV. The figure below (from Trane’s Ronnie Moffitt, in the ASHRAE Handbook S26.11) shows the reduction in energy recovery as a function of bypassed exhaust.
~Bill
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William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer
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From: Nicholas Caton [mailto:ncaton at catonenergy.com]
Sent: Monday, February 01, 2016 2:23 PM
To: Lapierre, Patrick <plapierre at bpa.ca>; Daniel Knapp <danielk at arborus.ca>; Miles H. Martschink <miles.martschink at rmf.com>; bfountain at greensim.com
Cc: equest-users at lists.onebuilding.org; Bishop, Bill <bbishop at pathfinder-ea.com>
Subject: RE: [Equest-users] Energy Recovery Wheel on VAV System
Count me as VERY happy to be corrected – thank you Patrick!
This certainly opens up some flexibility that I thought we were locked out of for some time. I’ll be re-evaluating my framework for these airflow relationships moving forward!
~Nick
NICK CATON, P.E.
Owner
Caton Energy Consulting
306 N Ferrel
Olathe, KS 66061
office: 785.410.3317
www.catonenergy.com
From: Lapierre, Patrick [mailto:plapierre at bpa.ca<mailto:plapierre at bpa.ca>]
Sent: Monday, February 01, 2016 1:08 PM
To: Nicholas Caton; Daniel Knapp; Miles H. Martschink; bfountain at greensim.com<mailto:bfountain at greensim.com>
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: RE: [Equest-users] Energy Recovery Wheel on VAV System
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:image011.png at 01D29F0B.B73360E0]
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:image012.jpg at 01D29F0B.B73360E0]
Patrick Lapierre_ing.
plapierre at bpa.ca<mailto:plapierre at bpa.ca>
De : Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] De la part de Nicholas Caton
Envoyé : 1 février 2016 13:51
À : Daniel Knapp <danielk at arborus.ca<mailto:danielk at arborus.ca>>; Miles H. Martschink <miles.martschink at rmf.com<mailto:miles.martschink at rmf.com>>; bfountain at greensim.com<mailto:bfountain at greensim.com>
Cc : equest-users at lists.onebuilding.org<mailto: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:image013.png at 01D29F0B.B73360E0]
This diagram illustrates my current understanding/impression of what plays into the exhaust airflow seen for recovery:
[cid:image014.png at 01D29F0B.B73360E0]
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
From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>] On Behalf Of bfountain at greensim.com<mailto:bfountain at greensim.com>
Sent: Monday, February 01, 2016 11:22 AM
To: Daniel Knapp
Cc: Miles H. Martschink; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Energy Recovery Wheel on VAV System
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.
From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>] On Behalf Of Daniel Knapp
Sent: Monday, February 01, 2016 10:42 AM
To: Miles H. Martschink
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Energy Recovery Wheel on VAV System
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<mailto: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<mailto:danielk at arborus.ca>
Energy Efficiency Expert
Arborus Consulting
76 Chamberlain Ave
Ottawa ON K1S 1V9
(613) 234-7178
On Feb 1, 2016, at 11:28 AM, Miles H. Martschink <miles.martschink at rmf.com<mailto:miles.martschink at rmf.com>> wrote:
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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RMF Engineering
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