In many apartment buildings gas consumption for hot water is measured by the volume of hot water used - not volume of gas. The conversion from hot water volume to gas consumption must assume an input cold water temperature and an output hot water temperature. What are these assumed temperatures, and how are they derived (for examle is the output hotwater temperature measured at the first tap in the apartment, or at the hotwater system often 10-100's meters away)? They appear to be assumed as constant - is this really the case?
Any light on this would be appreciated.
This is a great question. I can't give you details about your individual circumstances - you'll need to contact your building manager or body corporate who will be able to give you specific info, but in the meantime, here is a general explaination that may be useful:
In an apartment building, each unit is fitted with a sub-meter that records the amount of water used, while the distributor for the property records the amount of gas used to heat that water. In order to calculate your bill, the total amount of gas used is divided by the total amount of water used - resulting in a mega joules amount known as the common factor. Your hot water usage (recorded by your individual sub-meter) is then multiplied by the common factor. The result is the total amount of gas you will be charged on your bill.
Get in touch again if you have further questions - hope this has been helpful!
Thanks for the explanation - this is a very logical and generally fair way to measure gas consumption under these circumstances. The only issue I would have with this is the following:
In a centralised system such as exists in high rise buildings there is a loop of hot water piping, and to ensure that residents don't need to wait too long for the heated water to be available at their unit this loop continually circulates hot water from the top of the building to the bottom. This means a relatively 'fixed' but considerable amount of energy is used to heat this water which is not actually used by any customer, in fact it is wasted. So if the building is fully occupied this 'fixed' cost is spread across all residents - and that seems fair. If only 10% of the building is occupied (for some reason) then this 10% are billed the total 'fixed' cost. And, although unlikely, if only one resident was using hot water for a period they would pay all this fixed cost - which could increase their bill considerably - could be 10-100 times a normal account!!
So my question is, if there are no residents using hot water in any billing period who is billed for this fixed cost?
You'll have to speak to your property manager for an answer to this one.
It'll depend on how your building's hot water is managed - sometimes the centralised hot water system is owned and operated by the body corporate, other times by the retailer. Generally, the gas hot water used in common areas and property facilities is paid by the body corporate.
Once again - we can't speak for your individual situation so we encourage you to get in touch with your property manager for more info.
The following link to the Jemena Site gives an excellent overview of tthe design of Centralised Gas Hot Water Systems