[Equest-users] Energy Recovery Wheel on VAV System - zonal exhaust?

Fri Mar 17 13:08:03 PDT 2017

David,
Yes the RETURN-CAP-RATIO limits flow to the ERV, as long as zone exhaust AIRFLOW-TRACKING is not set to TRACK-SUPPLY or TRACK-BOTH. (I just tried modeling it.) If the zone exhaust tracks supply, there is no return to the air handler, and if there is an ERV it sees the total volume of zone exhaust.
The problem with specifying RETURN-CAP-RATIO or a system RETURN-FLOW that is less than the SUPPLY-FLOW is that fan energy for the return fan is only registered for hours when the system supply flow rate exceeds (SUPPLY-FLOW – RETURN-FLOW). For example, my 100% OA system has 23,000 cfm supply and 13,000 cfm return with the rest going to a lab exhaust fan and some exfiltration. There is no return fan energy reported until the hourly supply flow exceeds 10,000 cfm. Interestingly, the ERV fan power penalty associated with the system supply/return fans (when selecting HVAC-SUPPLY/RETURN for ERV-FANS) does not seem to be influenced by the zonal exhaust fan power even though the energy recovered is influenced by zonal exhaust flow.
~Bill

From: David Eldridge [mailto:DEldridge at grummanbutkus.com]
Sent: Friday, March 17, 2017 2:05 PM
To: Bishop, Bill <bbishop at pathfinder-ea.com>; Nicholas Caton <ncaton at catonenergy.com>; Lapierre, Patrick <plapierre at bpa.ca>; Daniel Knapp <danielk at arborus.ca>; Miles H. Martschink <miles.martschink at rmf.com>; bfountain at greensim.com
Subject: RE: [Equest-users] Energy Recovery Wheel on VAV System - zonal exhaust?

Does Return-cap-ratio limit the flow to the ERV? Since the dictionary excerpt below shows Return-cap-ratio in the context of exfiltration for your approximation Bill, it wouldn’t matter to you if the “modeled airflow” for recovery came from the zones or the central, since it is 100% OA there wouldn’t be any return – you are just looking for some BTU’s.

There should certainly be an easier (more accurate) way to flag zonal exhausts for inclusion or exclusion from the ERV, I’d suggest that to be added to the features list.

David

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop, Bill via Equest-users
Sent: Friday, March 17, 2017 12:09 PM
To: Nicholas Caton <ncaton at catonenergy.com<mailto:ncaton at catonenergy.com>>; Lapierre, Patrick <plapierre at bpa.ca<mailto:plapierre at bpa.ca>>; 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>
Subject: Re: [Equest-users] Energy Recovery Wheel on VAV System - zonal exhaust?

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
[cid:image002.jpg at 01D29F1D.191F37F0]

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

[cid:image004.jpg at 01D29F1D.191F37F0]  [cid:image006.jpg at 01D29F1D.191F37F0]

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[http://png-5.findicons.com/files/icons/977/rrze/720/globe.png]Carbon Fee and Dividend - simple, effective, and market-based.

From: Nicholas Caton [mailto:ncaton at catonenergy.com]
Sent: Monday, February 01, 2016 2:23 PM
To: Lapierre, Patrick <plapierre at bpa.ca<mailto:plapierre at bpa.ca>>; 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>; Bishop, Bill <bbishop at pathfinder-ea.com<mailto: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:image009.png at 01D29F1D.191F37F0]

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:image010.jpg at 01D29F1D.191F37F0]

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:image011.png at 01D29F1D.191F37F0]

This diagram illustrates my current understanding/impression of what plays into the exhaust airflow seen for recovery:
[cid:image012.png at 01D29F1D.191F37F0]

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
______________________________

RMF Engineering
Reliability. Efficiency. Integrity.

p: 843.971.9639
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