Modeling ISMRE

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Hi all,

ASHRAE 90.1-2013 addendum cd adds tables 6.8.1-14 and -15 which include an ISMRE requirement for "electrically operated DX-DOAS units, single package and remote condenser."

ISMRE stands for "Integrated Seasonal Moisture Removal Efficiency" and is measured in pounds of water removed per kWh of electrical energy consumed (lb/kWh).

TRANE has a great article on ISMRE and why it's now included in ASHRAE 90.1.

Currently, I'm working on a model with a parametric run for a DOAS unit with an ISMRE that is better than baseline, and an EER that is worse than the baseline.

How can I accurately model this improvement in ISMRE, and the resulting reduction in energy usage for the DOAS units?

Googling "eQuest ISMRE" returns only four hits, none of which are relevant.
Thanks,

Lee Shaver, Project Manager
Slipstream
608.210.7145 slipstreaminc.org

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Fascinating! (I've got deadlines today so naturally something catches my eye in the mailing list...)

On first pass through that article, it seems to me that the ASHRAE 90.1 committee dropped the ball with respect to considering performance rating energy simulation inputs.

There appears to be no immediately clear path for an energy simulator to get from a prescribed minimum ISMRE / ISCOP to a steady state EER or COP inputs you could apply to typical/library performance curves.

It might be possible to iteratively worsen the inputs of a standard DX unit accomplishing dehumidification and hot gas reheat to generate 70F air, then calculate its resulting "virtual lab" ISMRE / ISCOP rating using custom hourly reports for capacity/input at the stated testing conditions from the new standard 920 (tables in the linked paper summarize)... tweaking the weather/loading profiles may be necessary to replicate each testing condition - not a small venture. You could alternatively assemble all of the associated library curves and make a virtual benchmarking spreadsheet to model in parallel what doe2 would output for power in and capacity given [evaporator DB, evaporator WB, condenser DB, PLR], which would make it easier to punch in the various PLR and temperature conditions as variables. You could then run a solver function on the steady state EIR you'll enter for the unit to arrive at the exact/target prescribed rating. You could then post here and potentially sell copies of your work for 5 bucks a pop until 90.1 catches up... I'd pay that readily if a conundrum like this were in front of me today.

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Seems to me the ASHRAE Standard 90.1 committee has a little more homework to address this topic fully. I suggest either:

1. Come up with some concurrent steady-state performance criteria and a set of performance curves to fully describe the systems corresponding to the listed ISMRE / ISCOP ratings (rather than dump this legwork on all of the end-users, the majority of which will struggle and probably get the math wrong), or
2. Come up with a broad-stroke "derate" of the listed baseline efficiency for a normal DX system performing DOAS duties to fairly account for extra energies resulting from subcooling/hot gas reheat

Then again maybe I'm missing something... does this proposal make sense to anyone?

OK I better get back to work!

~Nick

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Hi Nick,
The tricky part is getting the performance data from the manufacturers. Back in the old days before the internet, the mechanical designer had huge binders from Trane, Carrier, etc. Those paper binders had much more performance data than available on line. You could pick up the performance of a unit at all those points in your table.

Christopher R Jones, P.Eng.
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As if energy modeling wasn't difficult enough, now we have ISMRE. (This is news to me.)
I agree with Nick that it's not immediately apparent how one would convert full-load MRE to EER or part load ISMRE to IEER, for simulating the comparative energy performance of DX DOAS units.
Additionally:

* 1.) Should you model an ASHRAE Appendix G Baseline any differently if the Proposed Design uses a DX DOAS?
* 2.) What inputs are available in eQUEST to capture the energy savings or penalty?

1. 90.1-2013 added a requirement in Table G3.1(4.) that temperature and humidity setpoints and schedules and control throttling ranges be the same between proposed and baseline. If the use of a DX DOAS in the proposed design is part of an active control strategy or requirement to maintain a known maximum RH value in the zones, then you would also use that humidity setpoint in the baseline. However, use of a DX DOAS does not by itself correspond directly with any particular zone humidity level. I don't think there are circumstances that require modeling a DOAS in the baseline. Likewise, if the proposed design has no zone humidity controls, I don't think you would model the baseline with any.
2. DX DOAS per Standard 920 specifies a leaving-air dew point no higher than 55?F. This can be modeled in eQUEST/DOE-2.3 with the new SYSTEM:MAX-DEWPOINT keyword. Some other keywords that might need custom inputs include RATED-EDB, RATED-EWB, COIL-BF and COIL-BF-FT. If use of a DX DOAS in the proposed design is an effective proxy for zone humidity control, you could specify SYSTEM:MAX-HUMIDITY in the baseline system(s), and also in any proposed design systems served by a DOAS (but not the DOAS itself). The SS-N reports summarize the RH values in the system return air. You could use these values from the proposed design reports to inform values for baseline MAX-HUMIDITY.

Cheers,
~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP
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