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HVAC Heat Loss Calculations and Principles

A. Bhatia, B.E.


Course Outline

The heat load is the amount of heat energy to be added to a building space to keep the indoor temperature within a specified range. This is the load that must be handled by the heating equipment. The heat loss calculation through a building fabric is the single most important step in determining the size the heating equipment. Proper sizing of heating equipment can mean savings in initial & operating costs and increased comfort to occupants.

This 4 - hour course provides a procedure for preparing a manual calculation for heat loss.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
Learning Objective

At the end of this course, the reader will:


Intended Audience

This course is aimed at students, mechanical and HVAC engineers, architects, energy auditors, O & M personal, building contractors, estimators, procurement personnel and engineers responsible for the design, purchase or upkeep of heating, ventilation and air conditioning systems.


Benefit to Attendees

Attendee of this course will get the technical oversight of the methodology to estimate the heat loss and perform energy analysis by manipulating the variables involved.


Course Introduction

The prime requirement in respect of the indoor climate in a building is that room temperature should be at a comfortable level, regardless of the weather conditions outside. As soon as the ambient temperature is lower than the indoor temperature, heat flows out from the building through its boundary surfaces (the building envelope). At the same time, the building also loses heat through air infiltration, i.e. the inward leakage of outdoor air into the building through gaps and cavities in walls, roofs, doors and windows. Bearing in mind the fact that the indoor temperature in most buildings is maintained at a little over 65°F, this means, throughout most of the year, the building is losing heat to its surroundings.

This course discusses the stepwise procedure to determine the rate of heat loss in detail.

Course Content

This course is in the following PDF document:

HVAC Heat Loss Calculations and Principles

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Course Summary

Heat loss calculations are carried out to estimate the capacity of heating systems. In order to establish the heat loss, we need to consider the following:

Where a temperature difference occurs between the inside and outside of a building, heat will flow through the structure towards the lower of the temperatures. This heat flow (loss) will occur through walls, floors, roofs, and windows, and even between rooms of dissimilar temperatures. It is important to know how much heat is lost through each structure so that calculations can be made to heat a building to the desired temperature. The transfer of heat is calculated using 'U Values' together with the surface areas of the various structural components and the temperature difference between the two sides of the structure concerned. For ease of calculation it is assumed that heat is lost at a uniform rate through each surface.

The ventilation air, flowing through the building, loses heat. Ventilation rates are usually quoted as 'air changes per hour' defined as the volume of ventilation air moving through the room per hour, divided by the volume of the room itself. The air will be heated by the heating system and the heat needed is calculated by multiplying the room volume, by the air change rate, by the temperature rise the air needs, and by the ventilation factor.

Once the heat loss is determined, heating equipment (radiator, convector or other centralized system) can be selected that provides an output to match the heat loss from the area under the same conditions. To improve a building's overall heating efficiency, it is helpful to understand what sources of heat loss create the greatest heating load. By reducing those loads, the heating system energy costs can be lowered and comfort can be improved.

 

Recommended Reading

Heat loss calculations are fairly straightforward, because they only involve sensible heat, i.e. the heat that you and I can feel. On the other hand, the cooling load is made up of two components, the latent heat and the sensible heat. The higher the average humidity in your area, the higher the latent load, which refers to the water vapor that must be condensed out of the air stream in your home to lower humidity. For further reading on the subject refer to the course titled “HVAC Cooling Load Calculations & Principles”.

This course gives an overview of heat gain principles for summer months and describes “How to estimate the cooling load using CLTD method”?

 

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.