HEAT LOAD ESTIMATING USING THE RULE OF THUMB 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 rule of thumb or check figures method.  This method allows a set number of watts per m² of floor space. This method doesn’t make any allowances for insulated or uninsulated ceilings or west or non- west facing walls. Neither does it allow for variations in the number of people occupying the space or the type of activity. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 This is the floor plan for a job I worked on recently.  The floor area is 5 m x 4 m = 20m². © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 The heat load is 2400 watts.  Therefore, this method of heat load estimation recommends a system with a cooling capacity of 2400 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