[Bldg-sim] Optimizing a DOAS

[David Eldridge]

Part of the attraction of the DOAS system with the fan-coil units is to reduce the amount of reheat needed in the building. You would have to be very efficient to provide simultaneous heating and cooling in a way that uses less energy than eliminating the simultaneous heating and cooling.

Generally you will be better off when you can reduce a load, rather than trying to provide that load through use of extra equipment. Understanding that the ability to program the sequence may not be infinite either, I think you are correct with your first thought to use the energy recovery equipment at little as possible while eliminating the need for reheat.

I’m not sure if I understand your second item about the chiller, but I think the same thought applies. Do you mean that the energy recovery system would false load the chiller to make it operate more efficiently, but at a higher load? The change in efficiency would have to be pretty dramatic to offset the additional MMBtu. Maybe there is some combination where it works out.

The other thought I had was if the control system has enough flexibility in the sequence of operations to account for some of the less frequent conditions. Particularly if the building operators are hands-on, it could be better to have a generically efficient scheme which might miss on a few infrequent conditions but over the course of the year provides a reliable energy savings.

Have you looked at TRNSYS as an option to simulate the components? Many of the flexibilities of EnergyPlus, but without the need to model the whole building. Unless you were going to model the building anyway.

David



David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates



From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Eric O'Neill
Sent: Thursday, March 21, 2013 4:15 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Optimizing a DOAS

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,





[Description: image41d3e6.PNG at 389a20b0] 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.michaelsenergy.com>  [Description: cid:image5fa2c8.PNG at 792ae6ae.438aa06e] <http://www.facebook.com/michaelsenergy>  [Description: cid:image504ae0.PNG at d838ed0a.4789ec2c] <http://www.linkedin.com/company/michaels-energy>  [Description: cid:imagec7bf83.PNG at aea7e03a.4882e7f2] <http://www.youtube.com/michaelsenergy>  [Description: cid:image48ea17.PNG at 40a6048e.43909589] <http://twitter.com/MichaelsEnergy>
MichaelsNRG


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130322/67e4c472/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.png
Type: image/png
Size: 2395 bytes
Desc: image001.png
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130322/67e4c472/attachment-0010.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image005.png
Type: image/png
Size: 678 bytes
Desc: image005.png
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130322/67e4c472/attachment-0011.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image007.png
Type: image/png
Size: 677 bytes
Desc: image007.png
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130322/67e4c472/attachment-0012.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image009.png
Type: image/png
Size: 284 bytes
Desc: image009.png
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130322/67e4c472/attachment-0013.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image013.png
Type: image/png
Size: 602 bytes
Desc: image013.png
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130322/67e4c472/attachment-0014.png>