Modeling different Energy Recovery Scenarios

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All,

Happy New Year!

I know that I recently asked the question shown below; however I did not
receive any replies so I thought I would try again seeing as how it's a
brand new year. The question as previously asked:

I am curious to know what programs/methodologies people have used to
effectively model the following types of energy recovery systems:

1.) Dual Wheel Heat Recovery with a Cooling Coil between the wheels.
This system is similar to the SEMCO Pinnacle system. As the outdoor air
travels through the air handler it passes first through a total energy
wheel, then through a cooling coil and then through a passive
dehumidification wheel. The exhaust air, as it leaves the building,
travels through the passive dehumidification wheel and then the total
energy wheel.

2.) Twice through Heat Recovery with a Cooling Coil in between the
first and second pass. This system is similar to a DesertAire system.
The outside air passes through the heat recovery device, through a
cooling coil, and then through the other side of the same heat recovery
device thus pre-cooling the outdoor air and reheating the supply air.

Please see the attached PDF for very simple schematic sketches of each
option.

Thanks,

Adam

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Hello Adam,

I haven't really simulated Energy recovery systems in such details. But I
believe ApacheHVAC module in IES VE could probably simulate the two systems.
The energy wheels can be represented by "Heat Recovery" item in ApacheHVAC
where inputs of sensible efficiency, latent efficiency as well as electrical
power consumption are necessary. For system A, two "Hear Recovery" items
are needed so that the total energy wheel and passive dehumidification wheel
can be modeled separately. Additional controllers may be necessary to
simulate the dehumidification wheel. Meanwhile, heat or cooling coil can be
placed in the air stream accordingly.

Regards,

Cheney

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Dear Adam,

Unless you?re very tightly connected to SEMCO, you?ll have to invent the passive dehumidification part of the Pinnacle unit. I don?t think that SEMCO has published anything like tech performance data for that wheel. It is NOT a standard energy recovery wheel.

James V. Dirkes II, P.E., LEED AP

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Adam,

We have also used spreadsheet calculations on the side for dual wheel energy recovery systems with coils between the wheels. Neither eQUEST nor Trane TRACE will model this type of system. When the coils have chilled water or hot water that we want to have TRACE (or eQUEST) include in the chilled water and hot water plants, we have the spreadsheet calculate the hourly cooling and heating coil loads, which can then be input into TRACE (or eQUEST) as hourly load profiles assigned to the respective plants.

Semco also has a spreadsheet calculator for the Pinnacle and other products on their website. It?s kind of hidden?

Go to www.semcoinc.com.
On the far left side select ?Energy Recovery Products.?
On the far left side select ?Pinnacle? (or whichever product you want)
Scroll down to the box at the bottom labeled ?Product Library.?
In the ?Select a category? field in the upper right corner of the box select ?Selection Software.?
Click on the spreadsheet icon and save the spreadsheet wherever you want.

There are a few quirky things to be aware of?

The natural gas utility cost is in units of $ per million BTU, which is 10 times $ per therm.

The cooling source kW/ton is for the entire system, including any pumps and cooling towers.

Electric consumption (kWh) is not calculated directly, but you can get it indirectly by setting the utility cost as $1 per kWh and $0 for everything else. Then the dollar amount shown matches the kWh. The gas consumption can be calculated indirectly in a similar way by entering $1 per million BTU (or $1000 to get more significant figures) and $0 for everything else. The same trick does not work for kW. I don?t remember why.

In the past we have experienced a problem with the Pinnacle spreadsheet not showing any change when the external static pressure is changed, so we did fan power calculations on the side. A quick check with the latest spreadsheet shows a change. Perhaps my original change from long ago was not significant enough to increase the cost by $1. (Some of my clients have very cheap electricity, which makes implementing efficiency tough sometimes!)

Keith Swartz, P.E., LEED AP

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Adam,

If there?s an answer it might be here: http://www.cmu.edu/iwess/publications/index.html#ventilation

Chaoqin Zhai wrote her dissertation on a Semco ventilation system that included a pair of wheels at Carnegie Mellon University while I was there writing mine. However, I believe this system used an active desiccant wheel with a total energy wheel.

There are several of her publications, which included input from folks at Semco, at the bottom of the link.

Good luck,

Fred Betz PhD., LEED AP

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Classification: UNCLASSIFIED
Caveats: NONE

Quick and easy.

Where do I get average energy prices? Is there a web-site I can type in the
city and state and get a cost?

Classification: UNCLASSIFIED
Caveats: NONE

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DOE's EIA site has these by state and utility (and user sector), suitable for LEED.

-DSE

Sent from my iPhone

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If modeling for LEED, I would advise seeking out the rate schedules for
the actual local utilities. It's a little extra work (actually I've
found the EIA site to be a pain to navigate in the past), but I suspect
those averages take into account huge industrial facilities and
government/military organizations with well-discounted rate structures
atypically lower than those used for a typical building owner's bills.
I've found plugging the actual rates in (for a few projects where I made
this comparison) to generally increase the consumption/demand costs
modeled, and often that can cause a better cost-based (i.e. LEED)
performance rating.

My $0.02,

NICK CATON, E.I.T.

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Well, John requested "no caveats"...but...good point Nick, I have done
more work on larger Midwestern facilities, so those have tended to be
consistent with EIA data. Your example is well taken that a smaller
facility might be expected to be higher than the EIA averages.

John, if the project is for LEED, the USGBC offers the EIA or a published
tariff as alternatives in the reference guide as Nick points out, and you
are certainly within your bounds to explore the options. If the project
is an addition to an existing campus, you may also have a custom agreement
in place that will cover the project. Be sure that you can document where
the rate comes from if you use it.

Also some states are deregulated electricity markets (such as Illinois) --
so even though you may find an applicable tariff (on ComEd's website as an
example) there are only a few customers that would use it. Most larger
clients in these states are purchasing electric commodity through a retail
energy supplier and using only the delivery rate from the utility.

In locations where demand charges are high, a project that takes measures
to reduce peak energy usage and demand could show a higher savings using
the tariff, since the EIA data is flat-rate. Definitely seek out the
actual information in these locations.

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, HBDP

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Seeking out actual utility rates is essiential for all the projects I've
been on. The averages from EIA are a good place to start, but often
times the actual rates are far higher, and this will lead to more LEED
points from the same design / engineering changes. I've also found that
using the actual utility rate for the baseline and using a discounted
utility rate that is applicable because of some incentive program is
allowed, and further increases the benefits from the cost-based approach
of LEED energy modeling.

Erik Turner EIT, LEED AP+BD+C

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John-
The statewide EIA rates are available for free if you are using TRACE 700 (and possibly eQUEST soon, keep reading), I maintain free updated library members (using EIA data)at http://energy-models.com/downloads (you do have to sign up to download, but it is free and we keep your address private)
It takes quite a while to maintain these rates, and I am currently in the process of automating the process for eQUEST (which is more work). However, there hasn't been too much interest in the TRACE 700 rates, so I don't know if it is worth making all the eQUEST rates. There is a survey on the homepage - energy-models.com - if you wish to show your interest to get this process expedited.
EIA rates are good for a start, but I agree with Nick about using the actual rates, especially since LEED points are based on $ savings and not energy. The EIA rates are "Linear" with energy vs. costs. However, in many actual rates, saving 10% in energy (or demand) may correspond with say 20% cost savings. LEED was intended to work in such a way, so that in "the big picture" there is greater energy savings, ie, utility companies can run more efficiently.
However, the average rates are a great place to start, no doubt, especially considering the complexity of many rate structures.
Anyway, if you are interested in eQUEST EIA values, please vote on the homepage at energy-models.com.
Thanks,
Bob

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