[Equest-users] ERV in Ottawa
Kelsey VanTassel
KVanTassel at sustaineng.com
Thu Dec 9 12:38:29 PST 2010
I find that ERVs use more energy when the Make-up Air Temp Ctrl is specified as "Float". In other words, there is no temperature control of the air leaving the ERV. For an enthalpy wheel, choose "Modulate HX". This allows the rotational speed of the wheel to vary in order to maintain a particular leaving air temperature.
Kelsey Van Tassel
Mechanical Engineer | kvantassel at sustaineng.com<mailto:kvantassel at sustaineng.com>
608.836.4488 ext. 20 | Fax: 608.836.4477
Sustainable Engineering Group
901 Deming Way, Suite 201
Madison, WI 53717
www.sustaineng.com<http://www.sustaineng.com/>
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Fleming, Joe
Sent: Thursday, December 09, 2010 2:12 PM
To: Daniel Knapp; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] ERV in Ottawa
I have come across this a lot in eQuest, and the solution for me is usually to only run the ERV in cooling mode, because I am usually in a mostly cooling climate.
I am not sure exactly how eQuest handles the ERV controls under "Operating Mode:", but it does say something in the help file that leads me to believe choosing heat/cool is a bad idea for an operating mode...
"OA-HEAT/COOL the default for enthalpy ERVs, indicates that the ERV will operate whenever the absolute value of the differential between the outdoor air and the exhaust exceeds the specified differential."
[cid:image001.png at 01CB97AE.8416EDF0]
The difference between OA cooling only or OA heating only and OA heat/cool is the term "absolute value". If the conditions are such that the absolute value between the exhaust and outdoor airflow is less than 5 degrees the ERV is off. If it is greater than 5 degrees the ERV comes on. So the entire period where you are in cooling mode but it is less than 70 degrees outside, (assuming a 75 degree space temp, abs|69-75| = +6, the ERV is adding to your cooling load and is hurting your cause, because we chose OA heat/cool.
If there were a way in eQuest to use an ERV in heat/cool mode but eliminate the absolute value part and make it +5 for cooling and -5 for heating, instead of Del_T > abs|OA-EA| then that would allow the ERV's to operate perfectly and operate in the same fashion as the standard ERV sequence in the field.
Does anyone know if this is correct, or if eQuest treats the control sequence different from what is described above?
Joe Fleming
E.I., LEED AP BD+C, BEMP
Mechanical Engineer I
TLC Engineering for Architecture
Your 2030 Challenge Partner
800 Fairway Drive, Suite 250
Deerfield Beach, FL 33441-1816
phone:Â
954-418-9096
fax:Â
954-418-9296
direct:Â
954-418-4591
website:Â
www.tlc-engineers.com
-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Daniel Knapp
Sent: Thursday, December 09, 2010 12:56 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] ERV in Ottawa
Hello,
I've been trying to understand how ERV works because I am finding the energy savings to be somewhat less than I had expected. Ottawa has a very cold climate in the winter and a warm, humid climate in the summer and I would expect enthalpy wheels to be a very good energy saving strategy. Instead, I am finding that in many cases the building uses more energy and in the best case scenario (OA exhaust DH, mixed air reset, modulate HX) on a VAV system saves only 0.15%. I have built a simple box model with one system in a two-storey office building and tried a number of different control strategies (see attached tables for results). I have tried a VAV and a SZ system. The ERV is able to save marginally more energy in the SZ system, but in neither case are the results what I was expecting.
My question is this: are these results to be taken at face value and believed or is there a better way to model ERVs in a Canadian climate? It seems very unlikely to me that ERVs cannot be controlled in such a way as to save significant energy in a climate of extremes. (.inp file attached as well).
With thanks and best wishes,
Dan
-
Daniel Knapp, PhD, 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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