Latent Heat Load Calculator
Free Latent heat load Calculator for hvac & plumbing projects. Enter dimensions to get material lists and cost estimates.
Formula
Q_latent = People Load + 0.68 x CFM x (Grains_out - Grains_in)
Total latent load is the sum of occupant latent heat (number of people times latent BTU per person based on activity) plus ventilation latent load (0.68 times outdoor CFM times the grain difference between outdoor and indoor air) plus infiltration latent (estimated at 10% of ventilation latent). The constant 0.68 comes from the latent heat of vaporization and air density in BTU per hour per CFM per grain.
Worked Examples
Example 1: Small Office Space
Problem: An office with 10 workers, 200 CFM outdoor air, outdoor grains 100, indoor grains 55.
Solution: People latent = 10 x 250 = 2,500 BTU/hr\nVent latent = 0.68 x 200 x (100 - 55) = 6,120 BTU/hr\nInfiltration = 6,120 x 0.10 = 612 BTU/hr\nTotal = 9,232 BTU/hr
Result: Total latent load is 9,232 BTU/hr (0.769 tons), removing 8.8 pints/hr of moisture
Example 2: Restaurant Kitchen Area
Problem: A kitchen with 5 cooks, 500 CFM outdoor air, outdoor grains 120, indoor grains 55.
Solution: People latent = 5 x 500 = 2,500 BTU/hr\nVent latent = 0.68 x 500 x (120 - 55) = 22,100 BTU/hr\nInfiltration = 22,100 x 0.10 = 2,210 BTU/hr\nTotal = 26,810 BTU/hr
Result: Total latent load is 26,810 BTU/hr (2.234 tons), removing 25.5 pints/hr of moisture
Frequently Asked Questions
What is latent heat load?
Latent heat load is the cooling capacity required to remove moisture from the air, as opposed to sensible heat load which lowers temperature. Latent heat comes from people breathing and perspiring, outdoor ventilation air carrying humidity, infiltration, and indoor moisture sources like cooking and bathing. The air conditioning system must handle both sensible and latent loads to maintain comfortable temperature and humidity. Latent load typically accounts for 25 to 35 percent of total cooling load in humid climates.
How does ventilation air contribute to latent load?
Outdoor ventilation air often carries more moisture than indoor air, especially in humid climates. The latent load from ventilation equals 0.68 times the outdoor airflow in CFM times the difference in moisture content between outdoor and indoor air in grains per pound. In tropical or Gulf Coast climates, ventilation latent load can exceed the people latent load significantly. This is why dehumidification is so important in commercial buildings with high ventilation requirements.
How do I reduce latent heat load in a building?
Several strategies reduce latent load. Use energy recovery ventilators (ERVs) that transfer moisture from incoming air to exhaust air, reducing ventilation latent load by 50-70%. Ensure the building envelope is well sealed to minimize infiltration. Use exhaust fans in kitchens and bathrooms to remove moisture at the source. Size the cooling equipment with proper sensible heat ratio to ensure adequate dehumidification. Oversized AC systems short-cycle and fail to remove enough moisture.
How do I calculate the load-bearing capacity of a beam?
Beam capacity depends on material, cross-section dimensions, span length, and support conditions. For a simple rectangular wood beam, bending strength = (F_b x b x d^2) / 6, where F_b is allowable stress, b is width, and d is depth. Always consult a structural engineer for critical applications.
What formula does Latent Heat Load Calculator use?
The formula used is described in the Formula section on this page. It is based on widely accepted standards in the relevant field. If you need a specific reference or citation, the References section provides links to authoritative sources.
Can I use Latent Heat Load Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.