I am modeling a 110,000 sf. Fedex sorting facility for LEED and the
building has a small office area that is heated and cooled by rooftop units and
the remainder of the warehouse is only heated.
In accordance with ASHRAE 90.1 2007 if no cooling system exists the cooling
system shall be identical to the system modeled in the baseline building
design.
That system is a system 5 packaged vav with reheat, which includes a hot
water boiler.
We have (15) gas-fired unit heaters that provide heat to the warehouse.
My question is do I set up my heating system with 15 hot water boilers, the
same heating capacity as the unit heaters?
For the fan energy, do I set my air quantity the same as my unit heaters?
How do I address the VAV portion of the system as well as the hot water
pumps?
I have my model setup with (2) separate HVAC systems (1) Packaged VAV with
Reheat and (2) Packaged rooftop DX units with a gas furnace.
Any help will be greatly appreciated.
Richard Dominick, P.E.
Richard:
I would base the model on one boiler/hot water loop with heating coils in each
air handler. As far as airflow, I would let eQuest autosize the CFM. Run the
simulation and if there are excessive unmet hours that cannot be corrected by
throttling range adjustments, try bumping up the airflow above the amount that
eQuest calculated.
Fan energy is calculated using the CFM, minimum motor efficiency and estimated
duct static loss per 90.1-2007 6.5.3.1.1A.
For the VAV portion, you can set the minimum and maximum fan ratios or you can
define a discharge air reset schedule.
Paul Diglio
Richard,
First check against the definitions of "space" on page 13. If the
rated capacity of the heating units for the space is between 3.4 Btuh/SF
and the value in Table 3.1 for your climate zone, then your warehouse
space is considered a semi-heated space and is not subject to the
requirement to model a cooling system in the baseline.
For the question on number of systems, what you're looking is under
G3.1.1: "For systems 5, 6, 7, and 8, each floor shall be modeled with a
separate HVAC system." That would mean a single system for the entire
warehouse portion of the building and the offices (unless you claim an
exemption for the offices due to G3.1.1.a, G3.1.1.b, G3.1.1.c, or
G3.1.1.d). Then note any requirements for system 5 from the latter
portions of appendix G.
Jeremy R. Poling, PE, LEED AP+BDC
Jeremy:
My space is subject to the requirements to model a cooling system in the
baseline.
This is where I am a bit confused. The office area has a specified cooling
and heating system (RTU) but the warehouse area only has a heating system -
15 unit heaters plus a ventilation system. The building is only one level
- so do I model just one cooling and heating system (system 5) or can I
model 2 systems? - one for the office and one for the warehouse?
If so how do I treat the fan energy from the unit heaters and the need to
model a boiler and hot water pumps, when no such system exists?
In a message dated 3/3/2011 4:13:10 P.M. Eastern Standard Time,
Jeremy.Poling at transwestern.net writes:
Richard,
First check against the definitions of ?space? on page 13. If the rated
capacity of the heating units for the space is between 3.4 Btuh/SF and the
value in Table 3.1 for your climate zone, then your warehouse space is
considered a semi-heated space and is not subject to the requirement to model
a cooling system in the baseline.
For the question on number of systems, what you?re looking is under
G3.1.1: ?For systems 5, 6, 7, and 8, each floor shall be modeled with a separate
HVAC system.? That would mean a single system for the entire warehouse
portion of the building and the offices (unless you claim an exemption for the
offices due to G3.1.1.a, G3.1.1.b, G3.1.1.c, or G3.1.1.d). Then note any
requirements for system 5 from the latter portions of appendix G.
Jeremy R. Poling, PE, LEED AP+BDC