Equest-users Digest, Vol 79, Issue 12

3 posts / 0 new
Last post

Hi Molly,

As far as Baseline system is concerned , we can choose the system type from
table G3.1.1A.
If the heating system for the building is Electric and hybrid, we can chose
the system type from the left column (i.e. System-1,3,5,7) from the table
Also, if the heating system has to be chosen, it should be considered from
the table G3.1.1B. For example for system type-3 the heating system for
Baseline Case is fossil fuel furnace.
Baseline case.
Hence the heating system can be chosen from these tables.
You have to keep in mind the type, area and number of floors of the

[image: Inline image 2]

Sharad. Kumar
Engineer, LEED-AP
Green Horizon Consulting LLP

Sharad Kumar's picture
Joined: 2014-10-16
Reputation: 0

Good morning, Molly,

Sharad is correct if the system in question is the Baseline HVAC system. With service hot water heaters, there is little guidance for the situation you describe and the modeling methodology is somewhat dependent on how often the back-up natural gas heater will be needed. If it is a rare occurrence, it would seem reasonable to treat the back-up heater as any other emergency back-up systems and ignore it. If the peak demand for the building is such that the natural gas heat will be required on a regular basis, it would seem reasonable to split the service hot water loads in both models so that the scheduled load on the Proposed heat pump water heater does not exceed the capacity of the proposed unit. In the Baseline case this same load would be met in the baseline case with an electric water heater. All loads that exceed the maximum for the heat pump would then be supplied by a natural gas water heater in both models with the actual thermal efficiency gas water heater in the Proposed case and a natural gas heater with the minimum prescribed performance from Table 7.8. As long as the supporting documentation clearly defines how the loads and schedules for the heat pump and natural gas heaters were determined, it should not be necessary to use the exceptional calculation method. Since this is an unusual strategy, it may be prudent to submit a project specific inquiry to GBCI before you take the time to delineate between the electric and natural gas loads in the models. The first step would be to run the proposed model and identify how often the back-up natural gas heat would be needed.

Hope this helps!

Cam Fitzgerald

Energy Opportunities/a 7group company

Cam Fitzgerald's picture
Joined: 2011-09-30
Reputation: 0

Hi Cam,
Thanks for your input. I was indeed asking about an appropriate baseline for a hybrid Service Water heating system (not HVAC system!) Your suggested approach seems reasonable, but I do agree with you that a CIR would be prudent.

Kind regards,

Senior Mechanical Engineer

719 Second Avenue Suite 400 Seattle WA 98104
t +1 206 749 9674 d +1 206 493 2234
f +1 206 749 0665

Molly Curtz's picture
Joined: 2011-09-30
Reputation: 0