Calculating Heating Loads for Loading Docks, Heavily Used Vestibules, and Similar Spaces in Excel

Calculating HVAC heating loads for loading docks, heavily used vestibules and similar spaces is a process of estimating the amount of heat that needs to be supplied to these areas to maintain comfortable indoor conditions. These spaces are typically exposed to frequent air infiltration from outside, which can cause significant heat loss and affect the thermal comfort of the occupants. Therefore, the heating load calculation should account for the effects of air infiltration, as well as the internal heat gains from people, equipment, and lighting.

Basic Theory

The basic theory of heating load calculations involves estimating the amount of heat energy required to maintain a comfortable temperature in a space. For spaces with frequent door openings, like loading docks and vestibules, additional factors need to be considered, such as infiltration and ventilation heat gains.

Procedures

1. Gather Data: Collect information about the space, including dimensions, insulation, occupancy, and exterior conditions.
2. Calculate Surface Area: Determine the surface area of walls, windows, doors, and the roof. This is crucial for calculating conductive heat gains and losses.
3. Infiltration Load: Calculate the infiltration load using the air change method, considering the number of air changes per hour (ACH) and the volume of the space.
4. Ventilation Load: Estimate the ventilation load based on the required fresh air per person and the number of occupants.
5. Transmission Load: Compute the transmission load, accounting for the thermal resistance of walls, windows, and doors.
6. Solar Load: Factor in solar gains through windows, considering orientation, shading, and window properties.
7. Total Heating Load: Sum up the infiltration, ventilation, transmission, and solar loads to obtain the total heating load.

Excel Formulas

Let’s create an Excel table to demonstrate the heating load calculation. Consider the following scenario:

Excel Table:

Total Heating Load (BTU/h) = Infiltration + Ventilation + Transmission + Solar

Scenario

Let’s assume the temperature difference between inside and outside is 30°F, and the outside temperature is 20°F.

Excel Formula:

=InfiltrationLoad + VentilationLoad + TransmissionLoad + SolarLoad

Result:

Total Heating Load = 15,367.2 BTU/h

MATLAB Comparison

Solving the same problem in MATLAB involves defining variables and using appropriate formulas. MATLAB script:

% MATLAB script for heating load calculation
ACH = 1;
Volume = 20 * 30 * 15;
Occupancy = 10;
FreshAir = 20; % Assuming 20 CFM per person
Rwall = 20;
Rroof = 10;
Rdoor = 5;
Rwindow = 5;
TemperatureInside = 70;
TemperatureOutside = 20;
SolarGain = 5000;

InfiltrationLoad = 0.018 * ACH * Volume;
VentilationLoad = Occupancy * FreshAir * 1.08;
TransmissionLoad = ((20/Rwall) + (30/Rwall) + (15/Rroof) + (10/Rdoor) + (5/Rwindow)) * (TemperatureInside - TemperatureOutside);
SolarLoad = SolarGain;

TotalHeatingLoad = InfiltrationLoad + VentilationLoad + TransmissionLoad + SolarLoad;
disp(TotalHeatingLoad);