Heat load by frost formation

[Sandro Baptista]

I wonder why I never see any one / or book calculating the total heat load of cold store or freezing tunnel with the inclusion of the latent heat load due to the ice formation. Part of the refrigeration capacity will spent on making ice so less capacity is available to cool down the air temperature and remove moisture from the air.

Usually I consider about 5%...8% of the total capacity to compensate this "negative" effect.

I'd like to hear your comments please.

[Sandro Baptista]

Hello......

[Magoo]

Generally I specify a blast application evap with progressive fin spacing , extra wide on air on face approx 1/3 of coil thickness the smaller spacing for rest of coil slab, the reduction of effective surface area means a larger coil more than 5 %. Snow builds on first part of coil but still allows air flow through coil.

[Sandro Baptista]

Generally I specify a blast application evap with progressive fin spacing , extra wide on air on face approx 1/3 of coil thickness the smaller spacing for rest of coil slab, the reduction of effective surface area means a larger coil more than 5 %. Snow builds on first part of coil but still allows air flow through coil.

Okay, but I'm not talking about evaporator design but rather heat load calculation. Part of the evaporator capacity is unfortunately used to generate ice and that will a heat load, so it will need more capacity to offset that effect.

[smpsmp45]

I think the Air Ingress given by Dossat considers this effect. Though actual Moisture entering in the room shall depend on many factors & the designers job is to avoid that, generally that Ingress factor is good enough for the calculations. If still there is an issue with the Frost- & it shall be there, We also take @ 5% extra capacity.

[Magoo]

Hi smp,
moisture ingress is difficult to control with blast freezing when the actual air pressure differential is effected by moisture removal, in effect a pressure difference in the enclosure. Added to the moisture collection on evap coils is the release of moisture from product, basically the lower the blast air temp to product the better, like -40'c or lower, the moisture does not have time to separate and weight loses from product is reduced. For long run period production runs in a blast freezer I would be effectively doubling the effective coil surface area and add progressive finning design on coils as well. As per a spiral freezer, nominal production in region of 16 hours before defrost required. Flooded coils is preferred for better constant coil slab temps., I have seen too many DX coils applied to blast freezing with minimal surface area that are iced up and non effective after 5 to 6 hours operation.