Latent Heat Loss Due to Infiltration Calculator

1. What is a Latent Heat Loss Calculator?

Definition: This calculator computes the latent heat loss (\( \dot{q}_l \)) due to infiltration air, based on the infiltration air flow rate and the indoor-outdoor humidity ratio difference.

Purpose: It is used in HVAC design to quantify the heat required to adjust the moisture content of infiltrating air, aiding in the sizing of humidification or dehumidification systems and improving energy efficiency.

2. How Does the Calculator Work?

The calculator uses the following formula for latent heat loss:

Latent Heat Loss: \[ \dot{q}_l = 4840 \times cfm \times \Delta W \]

Where:

\( \dot{q}_l \): Latent heat loss (Btu/hr, W)
\( cfm \): Infiltration air flow rate (ft³/min, m³/s)
\( \Delta W \): Indoor-outdoor humidity ratio difference (lb_v/lb_da, kg_v/kg_da)

Unit Conversions:

Air Flow Rate (\( cfm \)): ft³/min, m³/s (1 m³/s = 2118.88 ft³/min)
Humidity Ratio Difference (\( \Delta W \)): lb_v/lb_da, kg_v/kg_da (no conversion needed, as they are equivalent dimensionless ratios)
Latent Heat Loss (\( \dot{q}_l \)): Btu/hr, W (1 Btu/hr = 0.293071 W)

Steps:

Enter the infiltration air flow rate (\( cfm \)) and indoor-outdoor humidity ratio difference (\( \Delta W \)), and select their units.
Convert \( cfm \) to ft³/min; no conversion needed for \( \Delta W \).
Calculate the latent heat loss using the formula, with the constant 4840 Btu/hr per ft³/min-(lb_v/lb_da).
Convert the result to the selected unit (Btu/hr or W).
Display the result with 5 decimal places, or in scientific notation if the value is greater than 10,000 or less than 0.00001.

3. Importance of Latent Heat Loss Calculation

Calculating latent heat loss is crucial for:

HVAC Design: Determines the load required to manage moisture from infiltrating air, aiding in humidifier or dehumidifier sizing.
Energy Efficiency: Helps optimize humidity control to reduce energy consumption.
Indoor Comfort: Ensures indoor humidity levels are maintained for occupant comfort and health.

4. Using the Calculator

Examples:

Example 1: For \( cfm = 40 \, \text{ft³/min} \), \( \Delta W = 0.0038 \, \text{lb_v/lb_da} \), latent heat loss in Btu/hr:
- \( \dot{q}_l = 4840 \times 40 \times 0.0038 = 735.68 \)
- Since 735.68 < 10000 and > 0.00001, display with 5 decimal places: \( 735.68000 \)
Example 2: For \( cfm = 0.01888 \, \text{m³/s} \), \( \Delta W = 0.0024 \, \text{kg_v/kg_da} \), latent heat loss in W:
- Convert: \( cfm = 0.01888 \times 2118.88 \approx 40 \, \text{ft³/min} \)
- \( \Delta W = 0.0024 \, \text{lb_v/lb_da} \)
- \( \dot{q}_l = 4840 \times 40 \times 0.0024 \approx 464.64 \, \text{Btu/hr} \)
- Convert to W: \( 464.64 \times 0.293071 \approx 136.164 \)
- Since 136.164 < 10000 and > 0.00001, display with 5 decimal places: \( 136.16400 \)
Example 3: For \( cfm = 100 \, \text{ft³/min} \), \( \Delta W = 0.005 \, \text{lb_v/lb_da} \), latent heat loss in Btu/hr:
- \( \dot{q}_l = 4840 \times 100 \times 0.005 = 2420 \)
- Since 2420 < 10000 and > 0.00001, display with 5 decimal places: \( 2420.00000 \)

5. Frequently Asked Questions (FAQ)

Q: What does latent heat loss due to infiltration represent?
A: Latent heat loss (\( \dot{q}_l \)) quantifies the heat required to adjust the moisture content of infiltrating outdoor air to the indoor humidity level, affecting HVAC loads.

Q: How can I determine the humidity ratio difference?
A: The humidity ratio difference (\( \Delta W \)) is calculated from psychrometric charts or equations, using indoor and outdoor temperature and relative humidity data.

Q: Why is latent heat loss important in HVAC design?
A: It contributes to the HVAC load for humidity control, ensuring systems are sized to maintain comfortable and healthy indoor environments.