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Discussion:
Presuming you have studied the page on, "How
to use the ASHRAE Design Graph for Sensible Heating and Cooling
with Floor and Ceiling Panels", the above illustration
transposes the average fluid temperatures from various scenarios
(left side of picture) to the boiler efficiency based on
return
temperatures (right hand side). Essentially what this tells you
is that low return water temperatures which produce high boiler
efficiencies, come from using
highly conductive floors
heated with a high
tube
spacing density (less 12" O.C.) in
high performance buildings
(HPB)
having very low heating loads. For example, the highest
efficiency occurs when the return temperature is equal to the
average unconditioned surface temperature (AUST) of the space. This principle
also applies to heat
pumps and chillers and all other sources of heated and chilled
fluids. For further studies see our discussion on
effectiveness coefficients.
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