HVAC Cooling Load Calculations and Principles - a PDH Online Course for Engineers, Architects and Surveyors

HVAC Cooling Load Calculations and Principles

Course Outline

The cooling load is the amount of heat energy to be extracted from a building space to keep the indoor temperature, humidity and air quality within a specified range. This is the load that must be handled by the air-conditioning system. The calculation of the cooling loads is the single most important step in determining the size the cooling equipment. Proper sizing of HVAC equipment can mean savings in initial & operating cost of mechanical equipment and increased comfort to occupants. Equipment over sizing causes frequent cycling of equipment and poor dehumidification during cooling months.

This 5 - hour course provides a procedure for preparing a manual calculation for cooling load using CLTD/CLF method suggested by ASHRAE and includes two detailed examples.

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 conclusion of this course, the reader will:

Understand the basic terminology and definitions related to air conditioning load calculations;
Explain the differences between heating and cooling load design considerations;
Explain the difference between 1) space heat gain v/s cooling load 2) space cooling v/s cooling load and 3) external loads v/s internal loads;
Differentiate between sensible and latent loads;
List commonly used methods for estimating cooling loads;
Estimate the internal and external cooling loads using CLTD/CLF method from building specifications, design indoor and outdoor conditions, occupancy etc.;
Describe various equations to determine conductive load through opaque building elements;
Describe various equations to determine the solar transmission load through glazing;
Describe various equations to determine the internal load due to people, lights and power appliances;
Understand the influence of ventilation and infiltration on cooling load;
Determine the supply air flow rate;
Learn by examples the detailed methodology to cooling load calculations; and
Learn the functional parameters of software programs such as TRACE 700 and CHVAC.

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 cooling load and perform energy analysis by manipulating the variables involved.

Course Introduction

The cooling load for a building is the rate at which heat must be removed from it in order to keep the temperature, humidity and air quality within a specified range. This is the load that must be handled by the air-conditioning system. Its magnitude depends on outside climatic conditions, the construction materials, glazing, ventilation rates, lighting, equipment, occupancy and to the great extent; the design of the building.

To estimate the required cooling or heating capacities, one has to have information regarding the design indoor and outdoor conditions, specifications of the building, specifications of the conditioned space (such as the occupancy, activity level, various appliances and equipment used etc.) and any special requirements of the particular application. For comfort applications, the required indoor conditions are fixed by the criterion of thermal comfort, while for industrial or commercial applications the required indoor conditions are fixed by the particular processes being performed or the products being stored.

Generally, heating and cooling load calculations involve a systematic and stepwise procedure, which account for all the building energy flows. In practice, a variety of methods ranging from simple rules-of-thumb to complex transfer function methods are used to arrive at the building loads.

This course provides a procedure for preparing a manual calculation for cooling load using CLTD/CLF method suggested by ASHRAE and includes two detailed examples.

Course Content

This course is a PDF document.

HVAC Cooling Load Calculations and Principles

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Course Summary

Heating and cooling load calculations are carried out to estimate the required capacity of heating and cooling systems, which can maintain the required conditions in the conditioned space. To improve a building's overall cooling efficiency, it is helpful to understand what sources of heat gain or loss create the greatest cooling or heating load on the air conditioning system. By reducing those loads, air conditioning first costs and energy costs can be lowered and comfort can be improved.
There are two categories of cooling loads: 1) sensible cooling load and 2) latent cooling load.

Sensible heat is dry heat causing change in temperature but not in the moisture content. Factors that influence the sensible cooling load are glass windows or doors, sunlight striking windows, skylights, or glass doors and heating the room, exterior walls, partitions (that separate spaces of different temperatures), roofs, floors over an open crawl space, air infiltration through cracks in the building, doors, and windows, people in the building, equipment and appliances operated in the summer and lights. Other sensible heat gains are taken care of by the HVAC equipment before the air reaches the rooms (system gains). Two items that require additional sensible cooling capacity from the HVAC equipment are: ductwork located in an unconditioned space and the ventilation air (air that is mechanically introduced into the building).

Latent heat is the heat, when supplied to or removed from air, results in a change of moisture content - the temperature of the air is not changed. Factors that influence the latent cooling load are - people, moisture release appliances and air infiltration through cracks in the building, doors, and windows.
Note that the space heat gain and the space cooling load are “not” equal. Heat gain is the rate at which heat enters a space, or heat generated within a space during a time interval.

Space cooling load is the rate at which heat is removed from the conditioned space to maintain a constant space air temperature. The difference between the space heat gain and the space cooling load is due to the storage of a portion of radiant heat in the structure. The convective component is converted to space cooling load instantaneously.

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.