90.1-2010 Appendix G heat source question

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The proposed design has 9 floors and has heat recovery chillers, air-to-water heat pumps and natural gas boilers for the heating plant. Based on Table G3.1.1A, I selected System 5. Based on G3.1.3.2, I selected electric boiler as the predominate heat source is electric.

Based on G3.1.1 exception b. I have some spaces that require a single zone system. As the building has Fossil/Electric Hybrid heating, I select System 3 - PSZ-AC. My question is: should the heat source of these systems be gas furnace as per Table G3.1.1A or should I select electric resistance as the predominate heat source is electric?

Thanks for any insights!

Christopher Jones, P.Eng.
Halsall Associates
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Chris Jones
crollinjones's picture
Joined: 2013-12-12
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Chris - Here is some insight from a comparable situation, although the system types are different:

Three C&S office buildings that I've modeled have energy recovery ventilators (ERV-located on the roof) that use gas for heating. The terminal units throughout the building contain electric heating coils. The gas heating coil in the ERV is intended to be used in the following scenarios:

1) The energy wheel goes down

2) To keep the ERV discharge air temperature above 32F (heat air so the discharge is a minimum of 40F for freeze protection purposes)

For simulation purposes, I have found that, given the high efficiencies of the energy wheel and given the TMY3 weather data, the gas energy consumption is either not engaged at all or is sufficiently small compared to the electric energy consumption (<10% of total heating energy consumption).

For this reason, I have been able to justify going with System 4 or System 8. The energy savings of the proposed building when compared to the gas/electric hybrid baseline building is much less than the all-electric baseline building.


Nicholas E Blanton LEED AP BD+C
Mechanical Engineer

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I assume your building is non-residential. If that is the case the baseline system for a non-residential building with 9 floors must be System 7 or 8. Since the proposed building is gas/electric hybrid, that drives the baseline to system 7. Based on G3.1.3.2 your boiler will be fossil fuel. Systems qualifying for the exception under G3.1.1b should use the same heating source as the main system, so that means System 3.



Michael Rosenberg, CEM, LEED AP
Senior Research Scientist

Pacific Northwest National Laboratory
2032 Todd Street
Eugene, OR 97405
(541) 844-1960
michael.rosenberg at pnnl.gov

Rosenberg, Michael I2's picture
Joined: 2012-02-08
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Hi Chris,

1. >5 floors should be system 7 with hybrid heating source?
2. The selection of system for those special spaces in the building is
based on the heating source for the main building (Please see user's manual
p. G-28 for details). That's why you pick up system 3 which should be
fossil fuel furnace. You can not use predominate heating source here.

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chen yu's picture
Joined: 2011-10-02
Reputation: 200

A previous post from 2011 stated that the LEED reviewer provided the following comment:

?Section 1.1.A of the form indicates that the primary heating source is fossil
fuel. However, the electric heating energy use reported in Table EAp2-5 for the
Proposed Case exceeds the fossil fuel heating energy use. Please verify that the
correct heating source has been selected. If electric heating is the primary
heating source, please change the Baseline system type accordingly. Provide
updated simulation results and a revised Prerequisite Form as necessary.?

That is why I selected System 7 with an electric boiler (the predominate heating source is electric).

Should I not also selecte System 3 with electric heat for the special spaces even though the User Manual suggests fossil furnace?

Christopher Jones, P.Eng.
Tel: 416.644.4226 ? Toll Free: 1.888.425.7255 x 527

Chris Jones
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Joined: 2013-12-12
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