[Equest-users] ERV in Ottawa

[Carol Gardner]

Dan et.al.,

When modeling ERVs be sure to examine all of the input possibilities and
select the mode, operation, control, etc., that best meets your situation.
Never accept defaults at face value; they are often not the best choice.

Best,

Carol

On Thu, Dec 9, 2010 at 1:43 PM, Brian Fountain <bfountain at greensim.com>wrote:

>  I agree that heat recovery makes a huge difference on the heating load and
> have seen that in many models.  Try changing your cooling setpoint in the
> VAV model from "warmest" or "fixed" to "OA-Reset".
>
> Regarding separating out outdoor air heating loads -- the quick,  imprecise
> method is to look at the difference between the LS-C and the SS-D peak
> heating loads -- which you are already doing.  The primary difference
> between these two is ventilation. (but peaks could occur at different times
> etc.)
>
> The more precise method is to run your model with and without outdoor air
> (which is a pain).
>
> Note that EE4 only does the reduction of OA for zonal system types -- for
> other systems it is using heat recovery routines in DOE-2.1e.
>
> (Still haven't had a peek at your model -- hopefully tonight.)
>
>
> On 12/9/2010 4:26 PM, Daniel Knapp wrote:
>
> Hi Brian,
>
>  Your point about OA fraction and supply air setpoint is well taken, but I
> have also tried modelling this with 50% OA (25,000 cfm) in a single zone
> system at higher supply air setpoints of 95ºF without seeing much of a
> return.  Maybe my expectations have been set unreasonably high by EE4's
> crude method of cutting OA volumes to model ERV, but I still tend to think
> of OA heating as a fairly high fraction of the peak heating load in winter.
>   (ERV peak heating is nearly double the building peak loads (LS-C report),
> but is still a fraction of the HVAC peak load (SS-D report, which is partly
> so high because it's at building warmup)).
>
>  Is there a clear way to separate out the outdoor air heating load in the
> SIM file?
>
>  Thank you everyone for your thoughtful and helpful replies!
>
>  Cheers,
> 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
>
>
>
>  On 2010-12-09, at 1:30 PM, Brian Fountain wrote:
>
>  Hi Daniel,
>
> I haven't looked at your model yet -- will try and take a look this
> afternoon.
>
> One thing to consider is the outdoor air fraction and the supply air
> temperature setpoint.  If you have a low OA fraction, say 15% and a low
> supply air temperature, say 55F -- then often you will be mixing to satisfy
> that SAT and the heat recovery will only come into play for very cold
> temperatures.  Meanwhile, you will be adding static pressure on your system
> and seeing notable increased fan energy.
>
> On the other hand, if you have a dedicated outdoor air system then you will
> see dramatic savings with an ERV.
>
> I saw that you were playing with the ERV control -- FLOAT is the default
> and maximizes heat recovery always -- this would be typical of a heat pipe
> where you can't modulate the heat recovery.  Trim economizer is non-typical
> -- bringing in more OA to compensate for excess heat recovery.  I usually
> use MA reset.  Have a look at the ERV report in the .sim report to see
> actual heat recovered (plus the added fan energy which is NOT reported on
> the SV-A report and defaults at 1" for both supply and return).
>
> Brian
>
>
>
> On 12/9/2010 12:55 PM, Daniel Knapp wrote:
>
> 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+Mdanielk at arborus.ca
>
> Arborus Consulting
> Energy Strategies for the Built Environmentwww.arborus.ca
> 76 Chamberlain Avenue
> Ottawa, ON, K1S 1V9
> Phone: (613) 234-7178 ext. 113
> Fax: (613) 234-0740
>
>
>
>
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-- 
Carol Gardner PE
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