[Bldg-sim] 90.1-2010 Section 11 Baseline System modeling question

Jones, Christopher cjones at halsall.com
Tue Mar 24 09:23:40 PDT 2015

The project is to demonstrate compliance using Section 11 of 90.1-2010.  The proposed building has air-cooled heat recovery chillers that become air-to-water heat pumps when there is no cooling demand.  The plant has natural gas boilers for the coldest days and to bring the DHW temperature up when the heat recovery chillers don’t product high enough temperatures.  The HVAC systems are hydronically heated and cooled.

Is the Condenser Cooling Source Air/None?  Or as most of the rejected heat goes into the heating loop side, is the condenser Water/Ground?

Then 11.3.2.j.2 indicates that the systems that use the secondary heating source type shall be modelled identically in the budget case and the primary heating source shall be used to determine the budget system type.

What does “identically” mean – that the heating plant shall be identical?

For example, if one assumes Air/None as the condenser source, then the single zone systems would be System 11, rooftop air conditioner with fossil fuel furnace.  The multi-zone systems would be System 4, packaged rooftop VAV with reheat, hot water fossil fuel boiler.  But if they budget systems are to be “identical” would the heating plant in the budget case also be heat recovery chillers/heat pumps and boilers?

I am confused.

Christopher Jones, P.Eng.
Tel: 416.644.4226 • Toll Free: 1.888.425.7255 x 527

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