[bldg-sim] Energy Recovery in eQUEST

[Mike Tillou]

Shruti,

I think I can answer your questions. 

1. You can specify the static pressure drop of both the supply and
exhaust side of the ERV and eQuest calculates the fan energy assuming
that the main AHU supply and return fans pick up the extra static (this
is the default).  You can also specify dedicated fans for the ERV.  You
find this on the Second Heat Recovery tab.

2. I think the Bypass OA hourly value reports 0 whenever the ERV is off
because eQuest is assuming none of the OA is going through the ERV so
there is no air being bypassed to maintain the temperature control of
the ERV (in other words if the ERV is off, equest assumes it's not
there)

It's not obvious how eQuest does the ERV calculation.  If you look at
the hourly reports and the standard reports the effects of the increased
pressure drop of the ERV only show up in a few places.

The extra pressure drop does not show up in the SV-A report which
summarizes the fan system characteristics, nor does the extra fan energy
show up in the hourly report values of Supply Fan kW and Return Fan kW.

You can see the added fan energy in the monthly breakdowns in the SS-L
report but not in the breakdown of annual fan power usage in the same
report.

There is also an ERV report that gets included in the SIM file whenever
an ERV is simulated.  This report appears after the SS-N report for the
system with the ERV.  The report is NOT included in the report list
drop-down-box included with the D2SimViewer so you need to scroll down
past the SS-N report to find it.

Maybe one of the DOE2.2 folks could explain a little better how the ERV
is simulated and how the results get reported. 

Just be careful when you're calibrating the model and don't get
frustrated if it looks like its not working.  

Mike

Mike Tillou, PE
etc Group, Inc.




-----Original Message-----
From: bldg-sim at gard.com [mailto:bldg-sim at gard.com] On Behalf Of shruti
narayan
Sent: Wednesday, September 14, 2005 7:37 PM
To: bldg-sim at gard.com
Subject: [bldg-sim] Energy Recovery in eQUEST

We have modeled a 100% OA AHU system with Energy Recovery in eQUEST
based on 
the following control mechanism.

Enthalpy Wheel type- recovering both sensible and latent heat,
Operating mode - both heat/cool,
Make up air temperature control- Mixed Air Reset
Capacity Control- Bypass OA
Operation-OA Exhaust DT
OA/Exhaust DT- 5degF

As stated by others previously, the energy savings potential can vary 
markedly depending on the effectiveness of the control sequence. An ERV
that 
operates continuously can incur a significant fan energy penalty. In 
addition, it may recover heat when the heat is not needed, thereby 
increasing cooling energy. A properly controlled ERV may prove to be
cost 
effective, while the same ERV improperly controlled may actually
increase 
energy usage and cost.

The questions are:

1. To relieve the static pressure drop (not to provide control), a
bypass 
damper has been incorporated into the design on both the exhaust and
supply 
decks.  Intention is for the damper to open when the energy recovery is
off, 
thereby reducing the static pressure drop.  How should one model the
bypass 
dampers to accurately account for the static pressure relief...
perhaps a 
schedule of pressure drop or fan energy tied to the ERV status?

2. Also hourly reports obtained from the current model for " ERV
fraction of 
OA bypassed around the HX ". Indicate a fraction of air being bypassed
when 
the ERV is on, however it gives a value of 0 when the ERV is off, which 
should not be the case. The fraction of OA being bypassed should be 1
when 
the ERV is off. What could be wrong? Any thoughts or suggestions?

This perhaps adds onto the previous thread of in-depth discussion on
Energy 
Recovery, but having been through the Bldg-sim archive and the DOE 2
manual 
we have not been able to find an answer to the above issues. Any
direction 
would be really appreciated, either in the modeling inputs or using post

processing to get the Energy Recovery with bypass dampers to show
accurate 
savings.

Thanks



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