Selection of System 9 or 10 for heated only spaces

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Dear All,

We have a residential project with hybrid heating source (gas+electric) to
condition the dwelling and corridor spaces. There are few electric heaters
serving stairwells and storage spaces. As per exception 'e' of section
G3.1.1, ASHRAE 90.1-2010, the thermal zones designed for heating only
systems in the proposed design, serving storage rooms, stairwells etc. and
not exhausting or transferring air from mechanically cooled thermal zones
in the proposed design shall use system 9 or 10 in the baseline building

The query is whether the selection of system 9 or 10 is based on building
heating source (hybrid in this case) or as per unit heater's heating source

Thank you.


Mayank Bhatnagar

Senior Project Manager
*Environmental Design Solutions Pvt. Ltd. [EDS]*
D - 1/25
Vasant Vihar
New Delhi - 110057

Mayank Bhatnagar's picture
Joined: 2011-10-02
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Good morning Mayank,

There are 3 ASHRAE 90.1 interpretations I know of that identify various scenarios pertaining to Baseline system types in residential buildings. They are:
IC 90.1-2010-26
IC 90.1-2007-11

My understanding is that the heating only spaces would have to use System 9 since the primary system is hybrid. If the electric consuming heating only spaces total 20,000 sqft or more, only then could System 10 be used.

Sheila Sagerer
Senior Engineer, EIT, BEMP, LEED AP
Heapy Engineering
Ph: 937-224-0881
smsagerer at

Sent from my iPhone

Sheila Sagerer's picture
Joined: 2018-01-06
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In scenarios where both gas and electricity are used as a heating source
for the proposed system?for example, in the case of water loop heat pumps,
which might be served by a gas-fired boiler, or a specific building with
gas-fired dedicated outdoor air systems (DOAS) and all electric terminal
units for heating?both electric and gas are counted toward the area served
by the respective fuel type. Proposed building designs with systems like
these are considered ?hybrid? systems and map to the *fossil-fuel baseline*.

Hope this helps!!

On Tue, Jul 17, 2018 at 4:24 PM Mayank Bhatnagar via Bldg-sim <


Javed Iqbal, LEED AP, CEA
Sr. Energy Analyst

javed iqbal's picture
Joined: 2012-05-18
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Thank you Sheila and Javed. However, there is still a gap in understanding
the exceptions. The question is whether the exception should be combined as:

1. Exception "a" says about dominant and non-dominant space type; and
source of heating for more than 20,000 sqft area.
2. Exception "b" says about use of system 3 and 4 for different cooling
load and/or different schedule based on building heating source type
(explicitly written).

However, for exception "e" should it be combined with exception "b" or "a"?

Thanks again!


Mayank Bhatnagar's picture
Joined: 2011-10-02
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