HEAT LOAD ESTIMATING USING THE QUICK SELECT METHOD © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence.

HEAT LOAD HEAT LOAD ESTIMATING ESTIMATING USING THE USING THE

QUICK SELECT QUICK SELECT METHODMETHOD

© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

Hello, I would like to show you Hello, I would like to show you how I estimate heat loads using how I estimate heat loads using the quick select method.the quick select method.

This method of estimating heat This method of estimating heat load uses a simple sizing chart load uses a simple sizing chart and is most suitable for and is most suitable for domestic applications. A chart domestic applications. A chart like this gives estimated heat like this gives estimated heat loads for given floor areas (in loads for given floor areas (in square metres) with variations square metres) with variations for day or night operation and for day or night operation and for insulated ceilings and west for insulated ceilings and west facing walls.facing walls.


The chart has seven The chart has seven columns.columns.

A simple building A simple building survey will guide you to survey will guide you to which column is suitable which column is suitable for any particular for any particular application.application.


The first columnThe first column from from the left is the the left is the recommended cooling recommended cooling capacities of the air capacities of the air conditioners for the conditioners for the various floor areas and various floor areas and situations. For example, situations. For example, insulated ceiling, insulated ceiling, uninsulated ceiling, west uninsulated ceiling, west facing or other direction facing or other direction walls and day or night walls and day or night operation. operation.

The information is The information is obtained from the obtained from the building survey. building survey.


The second columnThe second column is is the floor area in square the floor area in square metres for applications metres for applications where the unit will where the unit will operate at night only. operate at night only. The ceiling is insulated.The ceiling is insulated.


The third columnThe third column is the is the floor area in square floor area in square metres for applications metres for applications where the unit will where the unit will operate at night only. operate at night only. The ceiling is The ceiling is uninsulated.uninsulated.


The fourth columnThe fourth column is the is the floor area in square floor area in square metres for applications metres for applications where the unit will where the unit will operate during day operate during day time. The ceiling is time. The ceiling is insulated and the walls insulated and the walls do not face west.do not face west.

FRESH OR FREEZING: HEAT LOAD ESTIMATING USING THE QUICK SELECT METHOD

The fifth columnThe fifth column is the is the floor area in square floor area in square metres for applications metres for applications where the unit will where the unit will operate during daytime. operate during daytime. The ceiling is The ceiling is uninsulated and the uninsulated and the walls do face west.walls do face west.


The sixth columnThe sixth column is the is the floor area in square floor area in square metres for applications metres for applications where the unit will where the unit will operate during daytime. operate during daytime. The ceiling is insulated The ceiling is insulated and the walls face west.and the walls face west.


The seventh columnThe seventh column is is the floor area in square the floor area in square metres for applications metres for applications where the unit will where the unit will operate during daytime. operate during daytime. The ceiling is The ceiling is uninsulated and the uninsulated and the walls face west.walls face west.


Let’s look at a recent job. Let’s look at a recent job. This is the floor plan for a bedroom we had been This is the floor plan for a bedroom we had been asked to measure for an air conditioning system.asked to measure for an air conditioning system.

The building surveyThe building surveygave this information:gave this information: the floor area is 20m²the floor area is 20m² the roof is insulatedthe roof is insulated the bedroom will bethe bedroom will be

for night use onlyfor night use only there are no westthere are no west

facing walls.facing walls.


Using the Using the second second columncolumn in the air in the air conditioning sizing chart conditioning sizing chart I can see that the I can see that the cooling capacity for 20 cooling capacity for 20 square metres is 2250 square metres is 2250 watts.watts.

This means that the This means that the quick select method for quick select method for estimating heat load estimating heat load recommends a system recommends a system with a cooling capacity with a cooling capacity of 2250 watts. of 2250 watts.


Once the heat load Once the heat load has been has been estimated, the next estimated, the next step is to select an step is to select an appropriately sized appropriately sized air conditioner. To air conditioner. To do this I need do this I need information from information from the air conditioner the air conditioner manufacturers. manufacturers. Most manufacturers Most manufacturers will have a brochure will have a brochure that contains the that contains the specifications of a specifications of a range of systems. range of systems.


We have to be careful when recommending We have to be careful when recommending the right size air conditioning system. the right size air conditioning system.

When a heat load estimate is calculated it When a heat load estimate is calculated it provides a guide to the required cooling provides a guide to the required cooling capacity for a system which will create capacity for a system which will create satisfactory conditions within the air satisfactory conditions within the air conditioned space. This calculation is made conditioned space. This calculation is made for a given set of conditions, and usually for a given set of conditions, and usually assumes an ambient temperature of about assumes an ambient temperature of about 32 °C and a relative humidity of about 65%.32 °C and a relative humidity of about 65%.

An over sized system will not always An over sized system will not always provide satisfactory performance. In some provide satisfactory performance. In some cases, a slightly smaller system may be cases, a slightly smaller system may be more desirable.more desirable.


An over sized system will rapidly cool An over sized system will rapidly cool the area without allowing sufficient the area without allowing sufficient time for de-humidification (moisture time for de-humidification (moisture removal). Frequent cycling of the removal). Frequent cycling of the system on and off by the thermostat system on and off by the thermostat can also result in more wear and tear can also result in more wear and tear than if the system runs steadily for than if the system runs steadily for longer periods.longer periods.

On the other hand an under sized On the other hand an under sized system will be incapable of providing system will be incapable of providing comfort during times of extreme heat. comfort during times of extreme heat.


HEAT LOAD ESTIMATING USING THE QUICK SELECT METHOD © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence.

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