[Bldg-sim] Optimizing a DOAS

[Eric O'Neill]

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,





[cid:image41d3e6.PNG at 389a20b0.47b7ac81]

 Eric L. O'Neill, P.E., LEED AP

 Managing Engineer - Implementation |  Michaels Energy

 Phone 608.785.3328 | Cell 608.792.7721

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