Latent case credit curves - should I normalise to T(amb) or T(case)?

asked 2019-07-13 12:11:44 -0500

Tilstergirl gravatar image

Hi folks, I'm confused about the guidance on appropriate latent case credit curve parameters for a set of supermarket refrigerated cases - I have a mix of tub-freezers and vertical multishelf cabinets, and am using the CaseTemperature method.

The Input-Output guide (1.34.2.1.12) says that the latent case credit curve should be normalised to have a value of 1.0 at the rated ambient air conditions of the case (for me that's 25 degrees C and 60% RH).

However, the Engineering Guide (eq 18.145) gives the Latent Ratio calculation as a function of case temperature, not ambient temperature, and Table 18.2 suggests values for the cubic parameters that are near-zero - they don't seem to be normalised. In fact the Engineering Guide doesn't mention normalisation.

I'm sure I'm missing something here. Should I just use the parameters directly from the Engineering Guide, or should I normalise the curve to equal 1.0 at some point? In which case, what value should I normalise to?

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