Heating and Cooling Load Calculator for Produce Coolers and Warm Rooms

This calculator provides an estimate of the heating or cooling load for a produce storage room of given dimensions, insulation, and sealing characteristics at a given set of temperatures. This calculator also accounts for product pull down and respiration loads. It does not account for other internal loads such as people, lights, or other motors. More information about cooling load calculations can be found in the Heatcraft Engineering Manual.


Target Inside Temperature (°F):

More information on storage temperatures for different crops can be found in the Crop Storage Planner or Handbook 66.

Quick reference:

  • Roots, cabbage, onions, garlic: 32 °F
  • Potatoes, tubers: 40 °F
  • Winter squash, cukes, peppers, tomatoes, sweet potatoes: 55-60 °F

    • Outside Design Temperature (°F):

    More information on outside design temperatures can be found in the Energy Star Design Temperature Limit Reference Guide.

    Quick Reference: In Vermont:

  • Winter (heating) design temperatures are between -4 and -18 °F.
  • Summer (cooling) design temperatures are between 84 and 87 °F.

    • Ground Temperature (°F):

    Ground temperatures can be found on the map at Build It Solar.

    Quick Reference: In Vermont, the range is 42 to 47 °F.

    Room Dimensions
    Width (ft):
    Length (ft):
    Height (ft):

    Insulation (hr-ft2-F/BTU)
    Wall R-value:
    Ceiling R-value:
    Floor R-value:

    Insulation R-values are typically given on a "per inch" basis and can be found at the Colorado Energy site.

    Quick reference: R-values per inch of thickness:

  • Polyurethane spray foam: 6.25 per inch
  • Foil faced polyisocyanurate: 5.6 per inch
  • Rigid extruded polystyrene board: 5 per inch
  • Mineral wool: 4 per inch
  • Wood lumber and plywood: 1.25 per inch
  • Concrete: 0.08 per inch.

    • The R-value of layered materials adds together. For example, 2 inches of polystyrene board (2x5=10) under 4 inches of concrete (4x0.08=0.32) has an R-value of 10.32.

    Sealing and Tightness
    Air Changes Per Hour (ACH):

    ACH is a measure of 'tightness', how well sealed the space is and how frequently the door is opened.

    Quick Reference: For long-term storage which is well-sealed with few door openings use 1. For a less well-sealed cooler or a walk-in with lots of traffic in and out, use something closer to 3 ACH.

    Product Pull Down Load
    Amount of Product (lbs):

    Specific Heat of Product (BTU/lb-°F):

    Temperature of Product Entering (°F):

    Storage Temperature of Product (°F):

    Time Allowed for Cooling of Product (Pull Down) (hr):

    Product "pull down" is the cooling energy rate required to bring a certain amount of produce from harvest / field temperature to storage temperature in a certain amount of time.

    Specific heat is the amount of energy (BTU) required to raise 1 lb of material 1 °F. For most produce a specific heat of 0.85 BTU/lb-°F is a reasonable assumption.

    The pull down cooling load is significantly influenced by the time allowed for the cooling of the product. A period of 24 hours is noted as a default above. For fresh market and highly perishable crops a faster pull down period may be needed while for storage crops a longer pull down period may be reasonable.

    Product Respiration
    Respiration Rate (mg/kg-hr):

    Product respiration is the heat produced naturally from stored, living produce.

    Respiration rate is given in units of mg of CO2 produced per kg of product per hour. The calculator converts this to BTU/hr based on product amount provided above. The rate of respiration decreases with temperature.

    Respiration rates are available in USDA Handbook 66.

    Quick reference: Some selected rates for common produce crops are provided below:

  • Apples (Fall, storage): 5 mg/kg-hr (between 32 and 41 °F)
  • Alliums (Garlic, Onions): 5 mg/kg-hr (at 32 °F)
  • Storage Root Crops (Beets, Carrots): 5-15 mg/kg-hr (at 32 °F)
  • Cabbage: 8 mg/kg-hr (between 32 and 41 °F)
  • Potatoes (cured): 12 mg/kg-hr (at 41 °F)
  • Tomatoes & Peppers: 19 mg/kg-hr (between 50 and 60 °F)
  • Sweet Potatoes: 20 mg/kg-hr (at 59 °F)
  • Leafy Greens, Lettuce: 21 mg/kg-hr (between 32 and 41 °F)
  • Cucumbers: 27 mg/kg-hr (between 50 and 60 °F)
  • Winter Squash: 99 mg/kg-hr (at 50 °F)

    • Results

    You will need to this space with BTU/hr (or watts). This figure includes no margin.

    Most referigeration systems are designed to run for 16 of every 24 hours (67% run time) to allow for defrost cycling. This results in a higher cooling load sizing point. In this case, that design point would be BTU/hr

    The use of window air conditioning units as a CoolBot(TM) system will require additional adjustment of this load due to the derate of the AC units. In other words, this number is not the size of the AC unit (or units) you will need. Consult the StoreItCold website for additional guidance.

    Details

    Heat Loss (+) or Gain (-) in BTU/hr:

    Total:

    Walls:

    Floor:

    Ceiling:

    Air Changes:

    Pull Down:

    Respiration:

    Wall Area: ft2

    Ceiling Area: ft2

    Floor Area: ft2

    Wall Perimeter: ft

    Inputs

    Temperatures:

    Inside: °F

    Outside: °F

    Ground: °F

    Dimensions:

    Width: ft

    Length: ft

    Height: ft

    Insulation R-value:

    Walls: hr-ft2-°F/BTU

    Ceiling: hr-ft2-°F/BTU

    Floor: hr-ft2-°F/BTU

    Air Changes per Hour:

    Product Pull Down:

    Amount of product: lbs

    Specific Heat: BTU/lb-°F

    Entering Temperature: °F

    Storage Temperature: °F

    Pull Down Time: hr

    Product Respiration:

    Respiration rate: mg/kg-hr

    Respiration rate: BTU/ton-day

    Respiration rate: BTU/lb-hr