Heat Recovery Chillers and Lab Outdoor Air

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Thanks in advance for any help.

1. I am trying to model a York heat recovery chiller for a lab facility
and one of the options on the table is adding a second injection rig to
boost the heat recovery capacity of the chiller. When I set the controls
and temperatures for a single rig, it operates closely to what my hand
calcs show for three months of operation in heat recovery mode. However,
I don't know how to boost the heating capacity in heating mode to
simulate the second rig. The heating capacity seems to be limited by the
cooling capacity. Do I need to do hand calcs and provide an exceptional
calculation which accounts for the derated chiller performance and
recovered heat? Any thoughts?

2. For the same lab, the baseline and proposed systems are 100% OA VAV
reheat. After all efficiency measures are included, the total system CFM
for the proposed model is 50,000 CFM less than the proposed, and because
it is a 100% OA system, the baseline system is providing an additional
50,000 CFM of outdoor air. Per ASHRAE G., the minimum ventilation
rates shall be the same, but changing the baseline model fundamentally
changes the way a 100% OA lab system is designed to work. If 100% OA is
not provided, then some amount of recirculation is assumed, and for labs
handling sensitive testing and materials, recirculation is not allowed
under any circumstance. Is there a CIR or addenda regarding this issue
in lab modeling? Any thoughts or experience are greatly appreciated.

Sam Mason

Sam Mason's picture
Joined: 2011-09-30
Reputation: 0

We've been modeling many complex / unusual situations like yours. In some
models our efficiencies come out great (high 30%s). Of course after looking
for CIRs, just put together all your documentation, wrap it up and send it
to the USGBC (it seemed like you were describing a LEED project). You'll
have two reviews, a design review after which you can answer questions /
modify design, and then a construction review. Key is to describe any and
every question you think they can ask you about the design and be sure to
write narratives in a manner that a person that doesn't know the project
can understand.

Additionally there's a section in 90.1 section 2.5, "This standard shall
not be used to circumvent any safety, health, or environmental
requirements." and 62.1's section 2.1 "This standard applies to all indoor
or enclosed spaces that people may occupy, except where other applicable
standards and requirements dictate larger amounts of ventilation than this
I believe the ventilation rates are to be kept the same in 90.1 for
breathing, building wash-out, and of course energy. I would think safety
would take precedence over these factors when your trying to compare apples
to apples.

What do you others think?


Shariq Ali EIT, LEED AP

Shariq_Ali at URSCorp.com's picture
Joined: 2011-10-01
Reputation: 200


Regarding point 2, I think the fundamental question is: what are the
code ventilation requirements for your facility? The proposed building
may require less total supply air due to efficiency improvements such as
less glazing, but there shouldn't be a difference in the amount of
outdoor air you have to provide. In fact, in hospital and lab
facilities, the total supply air is often also mandated. In Canada for
example, patient rooms must provide 2 ACH OA and 6 ACH total supply air.

That's why I think it's important to understand the code requirements.
If there is a code that governs how much outdoor air and total air must
be provided, then the same rates must be used in both proposed and
baseline buildings. Most, if not all, efficiency improvements will
reduce the amount of energy required to condition and move that air, but
the actually amount of outdoor air (and sometimes total air) should be
the same in both buildings, provided that you're not exceeding the
minimum ventilation requirements.

If a 100% OA system is a designer's/client's choice, but the same
building could be built to the governing code with say 33% OA, the
baseline building will use the minimum code rates, but the proposed
design should get penalized for over-ventilating. What I've found on
previous projects is that the code ventilation rates typically govern
the sizing of air-handling systems, meaning that the heating and cooling
loads can usually be met by the total ACH required by code for infection
control or required as make-up air when the fume hoods are operating.

I don't know if this has any bearing on ventilation rates and so it may
not help your situation, but I recall seeing a CIR requesting that the
Labs21 modelling requirements be used in lieu of Appendix G since the
latter penalizes lab systems. I think the response from the USGBC was
that the 2007 version of 90.1 addressed particular issues that made it
difficult for labs to get significant savings and therefore Labs21
should not be used.

I hope I haven't muddied the issue further with my comments.


Luka Matutinovic, B.A.Sc., LEED(r) AP

Matutinovic, Luka's picture
Joined: 2011-09-30
Reputation: 0


I agree with Luka's response most of the time. However, in laboratory facilities, the air change rates aren't typically dictated by code or ASHRAE, and usually the Client/standards/best practice drive them to be 100% OA. With regards to modeling and Appendix G, one way to interpret modeling approach is to see the Baseline system (i.e. System 7) as also being a 100% OA system. Thus, any ventilation or load driven spaces needing more than minimum ventilation are still being supplied with 100% OA. With Appendix G, one reading of the ventilation requirement is that the Baseline AHU should only be modeled with the minimum required OA cfm, with the remaining supply air needed to be from return air. This is what one recent reviewer stipulated. The issue with this that many modelers that understand labs will struggle with the fact that such a system would NOT be installed in a project because return air lab systems are practically non-existent. What we did see lately on a GBCI project review was the requirement to limit the Baseline OA to the minimum required no more than the Proposed OA, forcing us to have a return air lab AHU for the Baseline building. ASHRAE 90.1 and USGBC interpretations have often not been concerned with what is typical or "real" in the case of the Baseline building, it's really about energy. So, if other reviewers consistently rule this way, as we recently experienced, the message is that the energy target of 90.1 holds steady even for labs and outweighs the safety concerns of real design when considering the Baseline building. Thus, Proposed designs looking at chilled beams, fan coils, or other zone level systems used to decouple ventilation will be compared against a return air lab system. This will clearly reduce the potential to show savings between the two models.

Paul Erickson

Paul Erickson's picture
Joined: 2011-09-30
Reputation: 400

The item in 90.1 you pointed out is exactly the problem we are having
(and that 90.1-2004 does not address lab buildings). We just submitted a
lab/hospital building to the GBCI and included a separate narrative
which reads very similar to your email below, pointing out real life
construction and operation for 100% OA buildings (no recirculation air)
versus ASHRAE (with recirculation air). It sounds like the response we
will get from GBCI is to follow ASHRAE exactly, but we can hope.

Thanks for your input.

Sam Mason

Sam Mason's picture
Joined: 2011-09-30
Reputation: 0

Hi Sam,

You can contact Vanderweil Engineers in NJ as they did the energy modeling for the Yale Uninversity's Chemistry Research Lab Building when I was the sustainable design consultant for RETEC (working with Mark Loeffler - now at Atelier Ten).

Lee Schofer was the engineer at Vanderweil and hopefully they will give you full details on how they modeled the 100% outside air lab building per the USGBC's response to our LEED-NC v2.1 CIR. note the building received LEED-NC v2.1 Silver certification.

Debra Lombard, LEED AP, EIT

dlombard at earthlink.net's picture
Joined: 2011-10-01
Reputation: 0