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

HEAT LOAD HEAT LOAD ESTIMATING ESTIMATING USING THE USING THE

SHORT SHORT COMPREHENSIVE COMPREHENSIVE

METHODMETHOD

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

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

The short comprehensive method for The short comprehensive method for heat load estimating is used where heat load estimating is used where the construction of the structure or the construction of the structure or use of the space is considered use of the space is considered different to the expected average. For different to the expected average. For example, a living area where there is example, a living area where there is an unusually large amount of glass in an unusually large amount of glass in the walls, or where an area will have a the walls, or where an area will have a large number of people in it for long large number of people in it for long periods of time.periods of time.


To use this method I use To use this method I use some charts and forms. some charts and forms. Copies of these are in the Copies of these are in the Training Room. Training Room.

This is a chart for This is a chart for calculating heat through calculating heat through the ceiling and the floor.the ceiling and the floor.


This is a chart for This is a chart for calculating heat through calculating heat through the walls.the walls.


This is a chart for This is a chart for calculating heat through calculating heat through the windows.the windows.


This is a form for calculating the comprehensive heat load.This is a form for calculating the comprehensive heat load.


I have been I have been asked to asked to calculate the calculate the heat load for heat load for bedroom 1.bedroom 1.

Here it is on Here it is on the plan.the plan.


The building survey gave this information.The building survey gave this information.


Let’s have a look at my Let’s have a look at my calculations. There are a few calculations. There are a few steps. Here’s the first onesteps. Here’s the first one

Step 1Step 1 is calculating the heat is calculating the heat load through the ceiling and load through the ceiling and floor.floor.

If the floor area is 4 m x 5 m, If the floor area is 4 m x 5 m, total floor area equals 20 m². total floor area equals 20 m².

Use line A on the chart. It Use line A on the chart. It shows that the heat load shows that the heat load through the floor and ceiling through the floor and ceiling is is 200 watts200 watts..


200 watts200 watts is the is the first sub-total on first sub-total on the form for the form for calculating calculating comprehensive comprehensive heat load.heat load.


Step 2Step 2 is calculating the heat is calculating the heat load through the internal and load through the internal and external walls.external walls.

The internal wall length is 4 m The internal wall length is 4 m + 5 m, equalling 9 m+ 5 m, equalling 9 m

Use line A on the chart. It shows Use line A on the chart. It shows that the heat load through the that the heat load through the internal walls is internal walls is 360 watts.360 watts.

The external wall length isThe external wall length is4 m + 5 m, equalling 9 m.4 m + 5 m, equalling 9 m.

Use line D on the chart. It shows Use line D on the chart. It shows that the heat load through the that the heat load through the external walls is external walls is 600 watts.600 watts.


360 watts360 watts is the is the second sub-total second sub-total on the form for on the form for calculating calculating comprehensive comprehensive heat load.heat load.


600 watts600 watts is the is the third sub-total on third sub-total on the form for the form for calculating calculating comprehensive comprehensive heat load.heat load.


Step 3Step 3 is is calculating the calculating the heat load through heat load through the windows.the windows.

Total window area Total window area for the bedroom for the bedroom is 1.8 x 1.2 x 2, is 1.8 x 1.2 x 2, equalling 4.32 m².equalling 4.32 m².

If the windows If the windows had been either had been either west or south west or south facing, then facing, then multiplying or multiplying or dividing factors dividing factors would need to be would need to be applied.applied.


Use line C on the chart. It Use line C on the chart. It shows that the heat load shows that the heat load through the windows is through the windows is 1350 watts1350 watts


1350 watts1350 watts is the is the fourth sub-total fourth sub-total on the form for on the form for calculating calculating comprehensive comprehensive heat load. heat load.


Step 4.Step 4. The room to The room to be air conditioned is be air conditioned is a bedroom. a bedroom. Therefore Therefore 400 watts400 watts is added to the load is added to the load to compensate for to compensate for the heat produced the heat produced by the people by the people sleeping in the sleeping in the room.room.

400 watts400 watts is the is the fifth sub-total on fifth sub-total on the form for the form for calculating calculating comprehensive comprehensive heat load. heat load.


So the total cooling So the total cooling capacity for this capacity for this application is the application is the sum of all of the sub-sum of all of the sub-totals calculated.totals calculated.

Total heat load=200 Total heat load=200 + 360 + 600 + 1350 + 360 + 600 + 1350 + 400 totalling 2910 + 400 totalling 2910 watts. watts.

This means that an This means that an air conditioning air conditioning system, which has a system, which has a cooling capacity of cooling capacity of 2910 watts, will 2910 watts, will provide satisfactory provide satisfactory performance in this performance in this application.application.


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.


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