[BLDG-SIM] eQuest 100% OSA & Heat Recovery with System Type PZRH & SZRH Only?

[Brandon Nichols]

Thanks Steven and Mitchell

Excellent information, which I will compile/condense (with source credits, of course) and share on my energy modeling blog @ http://elcca-exchange.blogspot.com

Steve, your discussion of ERV assumptions caused me to rethink my simulation, from the perspective that my heat recovery coils are always in the air stream of the main air handlers.  So the 1/2" pressure drop across the heat recovery coils should be subtracted from the base case main air handlers, and added back in the parametric run, and presumably the ERV coil pressure drops zeroed-out.  

Curiously however, when I zero out the ERV pressure drops, set the base case SUPPLY-STATIC to 5.5" and RETURN-STATIC to 2.5", and use the parameters listed below in a comparison run, then according to the simulation the annual savings is 20% GREATER than than it was with SUPPLY-STATIC 6.0", RETURN-STATIC was 3.0" and the pressure drop across ERV coils were 0.5" each.

This is not coincident with my expectations, as I would expect additional energy recovery pressure drop to be experienced whenever the main air handlers are running in the former case, but only when the ERV is operational in the latter case -- resulting in the annual energy savings of the former case the LESS than that of the latter.

Any insights?  Much appreciated...


RECOVER-EXHAUST  = YES
ERV-RECOVER-TYPE = SENSIBLE-HX
ERV-RUN-CTRL     = OA-EXHAUST-DT
ERV-RECOVER-MODE = OA-HEAT/COOL
ERV-TEMP-CTRL    = FLOAT
ERV-CAP-CTRL     = MODULATE-HX
ERV-MOTOR-CLASS  = PREMIUM
ERV-OA-STATIC    = 0.0
ERV-EXH-STATIC   = 0.0
ERV-FROST-CTRL   = USE-CAP-CTRL 
SUPPLY-STATIC    = 6.0
RETURN-STATIC    = 3.0




-----Original Message-----
From: Steven Gates [mailto:steve.gates at doe2.com] 
Sent: Wednesday, February 28, 2007 9:07 AM
To: Brandon Nichols; BLDG-SIM at gard.com
Cc: Sudhir Avasare; Shawn Gavras; Eric Nordlund
Subject: RE: [BLDG-SIM] eQuest 100% OSA & Heat Recovery with System Type PZRH & SZRH Only?

Our research at the time we implemented the eQUEST/DOE-2 algorithm (approx 10 years ago) showed that 1" was typical.  However, that static did not include any pressure drop for filters upstream of both the exhaust and the OA inlets.  

Some manufacturers of heat-wheel ERVs state the wheels are "self cleaning", as the airflow reverses as the wheel rotates through each air stream.  I haven't seen one of these operating after 5 years without filters, so I don't know whether this is a valid claim or not.

My understanding is that all other types need a filter on each airstream or they will plug up over time.  The typical 30% filter has a pressure drop of about 0.5".  So the total pressure drop is on the order of 1.5"  Hence the
DOE-2 default.

The energy savings of an ERV is highly dependent on how it is controlled.
If it simply runs all hours of fan operation (the eQUEST default), it will almost certainly use more energy than it saves.  

Why such a poor default operating mode in eQUEST?  Our logic at the time was that, if the designer does not think about and specify the required control sequence, then the unit would be installed in the cheapest way possible, which is to simply interlock operation with the HVAC fans.  I have observed ERVs that run in exactly this manner...  

Steve Gates

-----Original Message-----
From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Brandon Nichols
Sent: Tuesday, February 27, 2007 8:48 PM
To: BLDG-SIM at gard.com
Cc: Sudhir Avasare; Shawn Gavras; Eric Nordlund
Subject: [BLDG-SIM] eQuest 100% OSA & Heat Recovery with System Type PZRH & SZRH Only?

Hello All,

First some generally useful information to model heat recovery parametrically.  The following parametric components were used to obtain about $5,000 savings on a $90,000 per year utility bill in the Pacific Northwest on a 'PSZ' system.  Most of them don't make much difference, the keys are the static pressure drops across the recovery coils, specified to be 0.5" in the HVAC design.  If the pressure drops are left at the eQuest defaults of 1.5", the system does not exhibit any net savings... all of the conserved natural gas is burned up in fan energy. 

RECOVER-EXHAUST  = YES
ERV-RECOVER-TYPE = SENSIBLE-HX
ERV-RUN-CTRL     = OA-EXHAUST-DT
ERV-RECOVER-MODE = OA-HEAT/COOL
ERV-TEMP-CTRL    = FLOAT
ERV-CAP-CTRL     = MODULATE-HX
ERV-MOTOR-CLASS  = PREMIUM
ERV-OA-STATIC    = 0.5
ERV-EXH-STATIC   = 0.5
ERV-FROST-CTRL   = USE-CAP-CTRL


So does this essentially answer my own question, just set the statics right and any system can be modeled with heat recovery?  I think the answer is 'no', because believe me I tried... there seems to me some deeper issues heat recovery-wise with some of the systems in eQuest/DOE2, not issues with the software necessarily, just issues I don't yet fully understand... hence any insights still appreciated.
  

BTW, all references in previous message to 'PZRH' system should've been 'PSZ'


Thanks
Brando



-----Original Message-----
From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Brandon Nichols
Sent: Tuesday, February 27, 2007 6:43 PM
To: BLDG-SIM at gard.com
Cc: Sudhir Avasare; Shawn Gavras; Eric Nordlund
Subject: [BLDG-SIM] eQuest 100% OSA & Heat Recovery with System Type PZRH & SZRH Only?

Hello All,

In simulating a 100% outside air heat recovery system with multistage DX cooling and supply air reset capability (40,000 CFM x2 units, in my mind a couple of big PVVTs), it was most time-consuming to learn by trial-and-error that heat recovery does not seem to work as expected for certain types of systems.  For the PVVT, PVAV, and VAV system types the baseline system would always outperform the heat recovery system, despite numerous iterations of parameter tweaking, and even if 'extreme measures' such as high internal heat loads were applied to force a large delta-T.

However when I at last selected a packaged or single zone reheat (PZRH or SZRH, after getting a clue from the BLDG-SIM archives)... Voilà!, reasonable results are instantly obtained.

My question is... do we need to stick to a list of simple systems when simulating heat recovery, regardless of whether its a 100% outside air system?  If so, does anyone have a list? So far, my list consists of just PZRH and SZRH, which seems a bit limiting.

Any empirical or quantitative insight into the mysterious inner workings of eQuest that would account for these observations much appreciated...


Regards

Brandon Nichols, PE
Mechanical
HARGIS ENGINEERS
600 Stewart St
Suite 1000
Seattle, WA 98101
d | 206.436.0400 c | 206.228.8707
o | 206.448.3376 f | 206.448.4450
www.hargis.biz

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