[Equest-users] ERV in Ottawa

[Fleming, Joe]

Thanks Kelsey, that's good to know.
For cooling savings float works fine for just cooling mode, but not heat/cool.  With the fixed set-point option it looks like the heat/cool mode works much better, it works the same as float in cooling only mode when you set the cooling temp down to 30.
But the ERV still operates outside of a typical control sequence and still undercuts the theoretical energy savings.
The heating load increases considerably in fixed setpoint mode, over float.
A constant wheel speed, an off mode, and a floating temperature is standard for the price devs will pay down here.
The optimal savings happens for heating in float and for cooling in float + cooling only.  The float heat/cool should be achievable, unless it butts heads with other system operations in eQuest.

DESIGN CONDITIONS & CONTROL STRATEGIES
Standard temperature control
The unit can be configured with normal air flows and
controls but still have the benefit of a large amount of
makeup air, better humidity control and lower
operating cost than a unit without a heat wheel. The
energy recovery unit operates in four (4) basic modes;
fan only; economizer; cooling and heating. Each of
these modes has specific functions as defined below.
Fan only mode: When the unit supply fan is started,
and there is no call for cooling or heating, the unit
economizer moves to its minimum position, the
heatwheel is activated and the heatwheel fan is
started. If the unit is equipped with heatwheel bypass
dampers, these are closed.
Economizer mode: With the unit supply fan in
operation and a call for cooling is made, if the outdoor
air temperature and humidity are below the enthalpy
setpoint, the heatwheel exhaust fan is activated, the
heatwheel is deactivated and the economizer
modulates to maintain the mixed air setpoint. If the unit
is equipped with heatwheel bypass dampers, these
are opened to accommodate the increase in outside
air volume.
Cooling mode: With the unit supply fan in operation
and a call for cooling is made, if the outdoor air
temperature and humidity are above the enthalpy
setpoint, the economizer moves to its minimum
position and mechanical cooling is activated. The
heatwheel is activated and the heatwheel exhaust fan
is started. If the unit is equipped with heatwheel
bypass dampers, these are closed.
Heating mode: Upon a call for heat, the heating
function is activated, the supply fan is activated and
the economizer moves to its minimum position. The
heatwheel is activated and the heatwheel exhaust fan
is started. If the unit is equipped with heatwheel
bypass dampers, these are closed.
Notice that in all four (4) basic above modes, the
operation of the heatwheel is determined by the
position of the economizer. With the exception of unit
shutdown or a night setback mode, the heatwheel
exhaust fan is in operation.
When control systems are "by others", all of the above
modes of operation must be considered.

As for Daniel's project, he is getting the short end of the stick on his heating savings when he switches to fixed setpoint and a shorter end when in float.
Maybe the weather file does not have enough high enthalpy days for the ERV to make a difference in cooling mode, (the enthalpy exchangers do make a big difference in cooling mode using a Miami weather file).

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:

954-418-9096

fax:

954-418-9296

direct:

954-418-4591

website:

www.tlc-engineers.com<http://www.tlc-engineers.com>


[cid:image002.gif at 01CB97B8.32158980]<http://www.tlc-engineers.com/>

From: Kelsey VanTassel [mailto:KVanTassel at sustaineng.com]
Sent: Thursday, December 09, 2010 3:38 PM
To: Fleming, Joe; Daniel Knapp; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] ERV in Ottawa

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:image003.png at 01CB97B8.32158980]





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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