[Bldg-sim] Optimizing a DOAS

[Dennis Knight]

Eric,
I have been looking at similar situations in our warm and humid climate for
about three years trying to optimize both DX and water cooled heat pump
DOAS with various combinations of heat recovery (sensible and total) and
have not found anything that can do a very good job of analyzing these
units under all oa conditions and varying return/exhaust air conditions.
I've played around with a spreadsheet solution as well using TMY3 weather
data for all 8760 hours and columns for heat transfer/temperature/humidity
across each device node in the process at each oa condition with fixed
return/exhaust conditions.
I will be very interested to hear/see if we get many responses to this.
These units are a big portion of the energy consumption in k-12 schools and
institutional occupancies in the warm and humid southeast. Thanks for
kicking this discussion off.
Dennis

On Thursday, March 21, 2013, Eric O'Neill wrote:

>   All,****
>
> ** **
>
> I’m working on a retrocomissioning project trying to optimize a DOAS
> system as best as I can. This particular system has (in this order) an
> enthalpy wheel, preheating steam coil, cooling coil, sensible wheel, and
> heating coil. Downstream there are 4-pipe fan coil units. Hot water is
> provided by a steam to hot water converter and a chiller with a closed
> circuit tower that can be switched over to free cooling when ambient
> conditions allow. ****
>
> ** **
>
> I’ve made myself an excel model, which has worked to some extent, but when
> I want to ask some of the more challenging questions it’s going to require
> a not-so-modest commitment to developing it (and circular references are
> driving me nuts). I’m fairly confident I can’t do what I want to do with
> DOE2 (with which I’m most familiar). Is E+ capable of modeling to this
> level of detail? Some of the types of questions I’d like answers to:****
>
> ** **
>
> **·         **When it’s extremely hot outside and the enthalpy wheel and
> cooling coil are running to dehumidify, is it more efficient to run the
> sensible wheel (near) full speed (thus lowering the exhaust temperature,
> allowing some additional cooling from the enthalpy wheel, and lowering the
> cooling coil load) or to do more modest reheating to balance the downstream
> cooling and heating demands? My gut says it’s going to be best to run the
> sensible wheel only as fast as is necessary to keep all the downstream
> heating coils closed, but I’d like some numbers.****
>
> **·         **When temperatures are mild, but not sufficient for full
> water-side free cooling, what’s the right balance between the enthalpy
> wheel and terminal cooling and heating? Is the chiller operating at a part
> load that’s more cost effective than the heating, and how does the enthalpy
> wheel strike the right balance? Is there a sequence that is optimum, or
> would it be something that needs to be continually optimized by the
> controls system?****
>
> ** **
>
> Obviously I’d need to go up the E+ learning curve, but I think that’s
> something I’ll need to do eventually (unless the fabled DOE2.3 engine comes
> out and can do this type of thing), so if it’s between that and continuing
> to develop a complicated excel model, it may be worth it for me. I just
> don’t want to go down that path only to find out I can’t get some of the
> answers I’m looking for…****
>
> ** **
>
> Any thoughts (or references) are appreciated. ****
>
> ** **
>
> Cheers,****
>
>
>
>
>
>  Eric L. O'Neill, P.E., LEED AP
>
>  Managing Engineer - Implementation |  Michaels Energy
>
>  Phone 608.785.3328 | Cell 608.792.7721
>
>  www.michaelsenergy.com  <http://www.facebook.com/michaelsenergy> <http://www.linkedin.com/company/michaels-energy>
>   <http://www.youtube.com/michaelsenergy> <http://twitter.com/MichaelsEnergy>
> MichaelsNRG
>
>
>
>

-- 
M. Dennis Knight, P.E.
Founder & CEO
*W*hole *B*uilding *S*ystems, LLC
P.O. Box 1845
Mt. Pleasant, SC 29465
Phone: 843-437-3647
Email: dknight at wholebuildingsystems.com
Website: www.wholebuildingsystems.com
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