[Bldg-sim] fossil hybrid or electric

Robby Oylear robbyoylear at gmail.com
Wed Aug 29 08:13:50 PDT 2012


Morgan,

I agree with Bill.  I find this LEED CIR (see below) to be helpful in
determining how fossil/electric hybrid systems should be handled.  Your
scenario sounds similar to item 5 under the examples of systems that would
be modeled with fossil fuel heating.

LEED Interpretations
11/1/2011 *ID#10132*

   - MPR/Prerequisite/Credit: *EAp2: Minimum Energy Performance*
   - Primary Rating System: *Core & Shell v2.0*

Email<https://www.usgbc.org/leedinterpretations/LIDetails.aspx?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>
Ruling

Clarification is requested regarding when a building heat source in Table
G3.1.1A should be identified as "Fossil/Electric Hybrid" versus "Electric".

The ASHRAE 90.1-2007 User's Manual states that a fossil/electric hybrid
source "refers to a system with any combination of fossil and electric
heat, and the baseline system for this is a fossil fuel system". Therefore,
the heating source for the proposed building would be considered "Fossil
Fuel" or "Fossil/Electric Hybrid" if the building uses any fossil fuel
source for space heating (including backup heating or preheating), and the
baseline building heat source would be fossil fuel.

Exception: ASHRAE 90.1 Section G3.1.1 Exception (a) stipulates additional
system type(s) for non-predominant conditions (i.e.
residential/non-residential or heating source) if those conditions apply to
more than 20,000 square feet of conditioned floor area.

EXAMPLES OF BASELINE HEATING SOURCE DETERMINATION:

The Baseline heat source from Table G3.1.1A for the following Proposed Case
system types would be fossil fuel since the proposed system design includes
a combination of fossil and electric heat:

1. Variable air volume system with gas furnace preheat and electric reheat
2. Packaged terminal heat pumps with outside air tempered by fossil fuel
furnace
3. Water source heat pumps with fossil fuel boiler
4. Ground source heat pumps with backup fossil fuel boiler
5. 90,000 square feet is conditioned by a variable air volume system with
electric reheat, and 10,000 square feet is conditioned with fossil fuel
furnaces

The following buildings would be modeled with an additional system type
with a different Baseline heating source in accordance with Section G3.1.1
Exception (a):

1. 90,000 square feet is conditioned by a variable air volume system with
electric reheat, and 20,000 square feet is conditioned with Packaged DX
systems with fossil fuel furnaces. In this case, the 90,000 square feet of
area would be modeled with an electric heat source in the Baseline Case
(System Type #6 - Packaged VAV with Electric PFP Boxes), and the 20,000
square feet of area would be modeled with a fossil fuel heat source in the
Baseline Case (System Type #3 - Packaged Single Zone AC with fossil fuel
furnace).
2. 50,000 square feet is conditioned by water source heat pumps with a
fossil fuel boiler, and 25,000 square feet is conditioned by electric heat
pumps. In this case, the 50,000 square feet of area would be modeled with a
fossil fuel heat source in the Baseline Case (System Type #5 - Packaged VAV
with hot water reheat), and the 25,000 square feet of area would be modeled
with an electric heat source in the Baseline Case (System Type #4 -
Packaged Single Zone Heat Pump).

Applicable Internationally.
Formal Inquiry

Table G3.1.1A lists two possible categories for the building heating
source:
(1) Fossil fuel, fossil/electric hybrid, & purchased heat;
(2) Electric and other.

In cases where the proposed building design includes both a natural gas
heating source and an electric heating source, when should the heat source
in Table G3.1.1A be identified as "Fossil/Electric Hybrid" versus
"Electric"?

Robby Oylear, PE, LEED AP

*Mechanical Engineer*

*Senior Energy Analyst*

* *

*D* 206-788-4571

*www.rushingco.com* <http://www.rushingco.com/>

On Tue, Aug 28, 2012 at 5:41 PM, Bishop, Bill <bbishop at pathfinder-ea.com>wrote:

>  Morgan,****
>
> ** **
>
> My vote is for PTAC with hot-water boiler.****
>
> ** **
>
> Regards,****
>
> Bill****
>
> ** **
>
> [image: Senior Energy Engineer 28Jun2012] <wbishop at pathfinder-ea.com>****
>
> ** **
>
> *From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
> bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Morgan Heater
> *Sent:* Tuesday, August 28, 2012 8:12 PM
> *To:* bldg-sim at lists.onebuilding.org
> *Subject:* [Bldg-sim] fossil hybrid or electric****
>
> ** **
>
> Hi – I’ve got an appendix G baseline system question.  Here’s the
> scenario, let me know what you think.  ****
>
> ** **
>
> Proposed Building:****
>
> ** **
>
> **1.       **Multi-family residential, amenity/common space < 20,000
> square feet****
>
> **2.       **Electric baseboard heat in the units****
>
> **3.       **Condensing gas furnaces in the corridors and back of house
> spaces****
>
> **4.       **VRF in amenity common spaces****
>
> ** **
>
> My understanding is that because my non-predominant condition
> (common/amenity space) is less than 20,000 square feet, I use a single
> system for the whole baseline building (G3.1.1a).  I’ve got a mix of gas
> and electric heat in the baseline building,  does this mean that my base
> system is PTAC with a hot water boiler?****
>
> ** **
>
> Thanks!  ****
>
> ** **
>
> ** **
>
> Morgan Heater, P.E.****
>
> BEMP, LEED AP****
>
> morgan at ecotope.com****
>
> 206-322-3753 ext 209****
>
> ** **
>
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