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90.1-2010 Section 11 - Interpretation for Zonal WSHP

asked 2016-07-19 14:13:25 -0600

Brett K gravatar image

updated 2016-07-19 16:33:33 -0600

Hi all - I'm hoping to solicit a few opinions on an interpretation of Section 11 rules for 90.1-2010.

I'm modelling a mid-sized office in Canada that uses zonal water-source heat pumps. The water loop is heated to around 60-70 degF by gas boilers, and is cooled by a water-cooled tower to around 90 degF.

What should the baseline system be per Section 11 (ECB) rules? On one hand I would suggest System Type 6, as heat is provided to the space via heat pump and it gives me a straightforward comparison between WSHP in the Proposed and Reference, with towers used for loop heat rejection in both cases (per note g of Table 11.3.2).

The alternative would be System 7. If I consider the building to be a control volume, heat pumps are not the primary energy source working to bring heat into the control volume; rather, the primary heating energy entering is the gas used in the boilers... With System Type 7 I would be comparing my Proposed WSHP+Boiler+Tower to the Reference FPFC+Chiller+Boiler.

Does anybody have any opinions they could share, official or unofficial as they might be?

EDIT: Minor additions to address Daniel's reply

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Assuming the cooling tower is water cooled?

Daniel gravatar image Daniel  ( 2016-07-19 14:46:47 -0600 )edit

Note g on Table 11.3.2A states that water source heat pumps will be connected to a common water loop with heat rejection by an axial fan closed-circuit evaporative cooler. So I don't think the DX cooling means that the condenser on the individual heat pump is air cooled.

Daniel gravatar image Daniel  ( 2016-07-19 14:49:22 -0600 )edit

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answered 2016-07-19 17:06:32 -0600

Section 11 in ASHRAE 90.1 is meant to be a 1 to 1 comparison. Every time I have been in this situation I have used system 6. Note G states that the condenser loop should be controlled between 60F and 90F with a fossil fuel boiler and a cooling tower, which is almost exactly like your proposed system.

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Asked: 2016-07-19 14:13:25 -0600

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Last updated: Jul 19 '16