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

 Hello, I would like to show you how I estimate heat loads using the quick select method.  This method of estimating heat load uses a simple sizing chart and is most suitable for domestic applications. A chart like this gives estimated heat loads for given floor areas (in square metres) with variations for day or night operation and for insulated ceilings and west facing walls. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 The chart has seven columns.  A simple building survey will guide you to which column is suitable for any particular application. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 The first column from the left is the recommended cooling capacities of the air conditioners for the various floor areas and situations. For example, insulated ceiling, uninsulated ceiling, west facing or other direction walls and day or night operation.  The information is obtained from the building survey. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 The second column is the floor area in square metres for applications where the unit will operate at night only. The ceiling is insulated. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 The third column is the floor area in square metres for applications where the unit will operate at night only. The ceiling is uninsulated. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 The fourth column is the floor area in square metres for applications where the unit will operate during day time. The ceiling is insulated and the walls do not face west. FRESH OR FREEZING: HEAT LOAD ESTIMATING USING THE QUICK SELECT METHOD

 The fifth column is the floor area in square metres for applications where the unit will operate during daytime. The ceiling is uninsulated and the walls do face west. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 The sixth column is the floor area in square metres for applications where the unit will operate during daytime. The ceiling is insulated and the walls face west. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 The seventh column is the floor area in square metres for applications where the unit will operate during daytime. The ceiling is uninsulated and the walls face west. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 Let’s look at a recent job. This is the floor plan for a bedroom we had been asked to measure for an air conditioning system.  The building survey gave this information: the floor area is 20m² the floor area is 20m² the roof is insulated the roof is insulated the bedroom will be for night use only the bedroom will be for night use only there are no west there are no west facing walls. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 Using the second column in the air conditioning sizing chart I can see that the cooling capacity for 20 square metres is 2250 watts.  This means that the quick select method for estimating heat load recommends a system with a cooling capacity of 2250 watts. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 Once the heat load has been estimated, the next step is to select an appropriately sized air conditioner. To do this I need information from the air conditioner manufacturers. Most manufacturers will have a brochure that contains the specifications of a range of systems. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 We have to be careful when recommending the right size air conditioning system.  When a heat load estimate is calculated it provides a guide to the required cooling capacity for a system which will create satisfactory conditions within the air conditioned space. This calculation is made for a given set of conditions, and usually assumes an ambient temperature of about 32 °C and a relative humidity of about 65%.  An over sized system will not always provide satisfactory performance. In some cases, a slightly smaller system may be more desirable. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 An over sized system will rapidly cool the area without allowing sufficient time for de-humidification (moisture removal). Frequent cycling of the system on and off by the thermostat can also result in more wear and tear than if the system runs steadily for longer periods.  On the other hand an under sized system will be incapable of providing comfort during times of extreme heat. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence