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RE: [EnergyPlus_Support] Heating and Cooling vs. U-value




Dear Vinay,



There are indeed many variables!



Generally (probably always) more insulation in the envelope will reduce heating costs.  The cooling costs are another question. 

The big part of the question is whether most of the load comes from outdoors (sun and temperature) or indoors (lights and plug load).  There?s also an influence from the schedules and diversity of the internal loads.

The building with a lot of internal load sources may see cooling costs increase with more insulation because one avenue for the internal loads to leave the building is the walls and the greater insulation prevents this.

So, I think you need to experiment a bit with your particular project, its internal loads and schedules, and the weather file.



p.s., As I recall Larry Spielvogel wrote an article discussing this in the ASDHRAE Journal probably 25 years ago.  It was completely counterintuitive, but made perfect sense once he explained the logic.

Similarly, Steve Taylor and C. Hwakong Cheng wrote a recent article in the ASHRAE Journal (November 2010) about why enthalpy economizers are LESS effective than a simple dry bulb economizer.  Perfectly counter-intuitive, but the rationale is unassailable.  Check it out!




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