ASHRAE 90.1-2013 Appendix G - Baseline Fuel Source Mapping

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Hello Everyone,

Does anyone know why the AHSRAE 90.1-2013 Appendix G Table G3.1.1-3 requires a Baseline HVAC system that is fossil fuel based for climate zones 3b,3c and 4-8? If my Proposed Design has an electric GSHP or VRF system, there is very little chance that the energy cost of this Proposed Design is going to be lower than a Baseline with a gas furnace/ boiler. Why does it matter for ASHRAE where the building is located and type of heating system selected for a project?

For folks in the New York, NYSERDA has amended this map to avoid this fuel switch which makes total sense.

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Thank you


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Madhav Munshi3's picture
Joined: 2014-01-17
Reputation: 0

Not sure if I missed a response to this or not...sorry this got lost in my draft folder for a few days.

What you've stated as the problem is exactly why the standard takes the other approach - if the baseline system costs less to operate (and may also have lower source energy) then why shouldn't it be the baseline system?

The standard is looking to establish the minimum requirements, which shouldn't be "Best Practice" necessarily but reflect a constantly advancing minimum threshold.

Choosing to use a system that's less cost efficient is certainly allowable and, but requires making other improvements in the building to offset what is traded off by using the electric resistance heating system.

Note that while the requirements of the standard do change based on climate, it isn't based on geography directly, I have understood in the past that the approach is for national average utility rates to set the requirements. I can think of several reasons why NYSERDA specifically would take a different approach, but in general for country-wide adoption I would expect gas heat to be the reasonable baseline in climate zones that need more heating. Is it debatable for zones 3b and 3c, perhaps. I'm pretty comfortable with fossil fuel baseline in CZ 4-8.

Separate topic: you are seeing GSHP and VRF systems use (much) more energy cost than the baselines?


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David Eldridge's picture
Joined: 2012-05-08
Reputation: 1

Madhav/ David,

I am thinking aloud here -
Climate zones 1-3a are not expected to have very low winter temperatures
and most of the heating requirement can be met with a heatpump with some
supplemental electric heat. While in Climate zones 4-8, we might need a
backup heating source.

Therefore, I understand why ASHRAE 90.1 would change the baselines based on
climate zones, in order to push the boundaries, as far as energy is
concerned. I still think a GSHP or a VRF would be competitive when you
compare their energy consumption to the 90.1 fossil fuel Baseline for
climate zone 4-8. However, if you consider only energy cost, it may be
harder to justify GSHP or VRF to your clients depending on the the cost of
natural gas in your area. Does an ASHRAE baseline system really dictate the
choice of the HVAC system or the fuel type in the proposed building?

Is the concern more to do with meeting energy cost saving targets ?

I would be interested to hear more thoughts on this topic.

Ramya Shivkumar

r s's picture
r s
Joined: 2013-07-02
Reputation: 2

I can share one story. We had a small non-commercial project in CZ7 considering LEED and asking us for recommendation of mechanical system. Under the old fuel source neutral Appendix G, we compared a ground source heat pump system to PSZ-HP with electric resistance below ~35F and we compared an AHU with condensing boiler to PSZ-AC with gas burner. The Appendix G costs savings, including other non-mechanical impacts, were ~55% for GSHP and ~27% for AHU with condensing boilers, yielding a 5 LEED point differential. Comparing solution to solution, the GSHPs really saved a modest ~9% in energy costs compared to the AHU and condensing boiler and the GHSPs had a larger carbon footprint.
A baseline mechanical system that uses lots of hours in electric resistance heating in a cold climate is a straw man for gauging leading performance because they are so rarely actually built. I have never been involved in standard development but I assume cases like this were at least part of the motivation.

Paul Riemer, PE, LEED AP BD+C

Paul Riemer's picture
Joined: 2011-09-30
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