Hi there,
I am responding to some LEED review comments regarding a small
building in Hawaii that only has 2 thermal zones. In reality one of
these zones is conditioned (small split system cooling only) and one
zone is unconditioned (naturally ventilated, no heating or cooling).
The LEED reviewer writes:
"ASHRAE 90.1-2004 Table G3.1.1(b) in the proposed building column
requires that all spaces that are conditioned and occupied in the
proposed design should be simulated as being both heated and cooled
even if no cooling or heating systems are to be installed per Table
G3.1.1(b) in the proposed building column." - this comment makes sense
per G3.1.1b.
The comment continues "Based on the building area, number of floors,
and principal heating source, system type 4: packaged rooftop heat
pump should be modeled for the unconditioned spaces and heating
component of system type 4: packaged rooftop heat pump should be
modeled for the conditioned office spaces unit. Please revise the
proposed and baseline models by modeling the same system type in both
cases in the unconditioned spaces and include heating equipment for
the conditioned office spaces." This second comments seems to say that
I need to put System Type 4 in the unconditioned space in both the
baseline and the proposed model ... does this seem to correct to
others?
If so, it seems to imply that you can never truly have an
unconditioned space in a LEED model? As a workaround, I plan to then
put the setpoints for cooling and heating such that those installed
systems will never turn on (which makes me wonder why a system should
be installed). If I don't do wide setpoints, my proposed model will
not be representative of the actual energy use of the design building.
Any thoughts on this topic would be much appreciated.
Caroline E. Fluhrer
Caroline,
I'd argue that the space is unconditioned and requires no heating or
cooling, provided it really is "unconditioned" per the ASHRAE
definition. (See below.)
Per the ASHRAE 90.1 User's Manual (2004 & 2007), p. G-21, regarding
requirements for modeling both heating and cooling:
"This requirement only applies to conditioned space in the building.
Semiheated spaces would only have a heating system; unconditioned spaces
would have neither heating nor cooling systems."
Your "unconditioned zone" meets the ASHRAE definition (see p.13 in the
Standard) unless it is an "enclosed space...heated or cooled indirectly
by being connected to adjacent spaces" and receives 3 air changes per
hour of transfer air.
Regards,
William Bishop, EIT, LEED(r) AP
Caroline,
I agree with Bill's remarks and you should first see if you can define
that space as "unconditioned" per ASHRAE's definition to get out of the
requirement all together.
All,
I wanted to see what others peoples thoughts are when we have these
conditioned spaces and must provide heating or cooling even if we really
do not have them in proposed design per Table G3.1, 10. HVAC system. I
have used the method Caroline mentions of raising or lowering set points
in these "non-existing" systems to reduce or eliminate any effect on
simulation comparison. This seems like a good approach, just wondering
if anyone else thinks this is a valid way to go about this? A common
case for us would be a data room, where cooling is only provided or a
mechanical equipment room where heating is only provided and heating
output capacity is above the 3.4 Btu/h-sf.
Thanks,
Tyler Whately, E.I.T.
Caroline,
Our assumption is that this provision was created to avoid giving projects credit for eliminating air conditioning on a project for energy savings without providing reasonable means for thermal comfort for occupants. We have been involved in a number of warehouse projects that have the same problem, since warehouses are rarely air-conditioned and only some meet the definition of semi-heated spaces.
Be sure to note the following CIR issued by the EA TAG when you provide your response as it justifies your temperature setpoints (we usually print a PDF from the USGBC website and submit that PDF as a supporting document):
LEED-NC v2.2 EAc1 CIR 4/14/2009:
3/20/2009 - Credit Interpretation Request
This project is to renovate 300,000 square feet of an old factory and convert to a distribution center. The owner strongly desires to be sustainable and will use many sustainable features whether or not LEED certification is sought. We will use high efficiency lighting and high efficiency infrared heaters, but no cooling. If we use the ASHRAE appendix G, we have to model the baseline cooling system for the baseline and the proposed.
Since the cooling energy will be much larger than the heating energy the 14% reduction from ASHRAE will not be possible. This force the project to be penalized for energy never actually used. In this case we feel that the ASHRAE standard does not rationally apply.
This project will reuse a large facility and incorporate significant sustainability features and we would not like to be excluded because the ASHRAE standard does not apply logically to this facility.
Is there any alternative method for compliance in this situation?
4/14/2009 - Ruling
The project has requested clarification regarding the use of the ASHRAE Baseline requirements in Appendix G. Although a cooling system must be modeled in both the Baseline and Design case, there are no requirements for Temperature Setpoint. Therefore, both cases may have the Cooling Temperature Setpoint elevated such that both systems do not ever run and thus does not consume any energy.
JEREMY R. POLING, PE, LEED AP