Our new home is well under way, and I am looking at monitoring various parts of the house and systems. The first I am looking at is the gas storage hot water service.
With the hot water system, I want to monitor the water flow, gas flow and the temperature at the top and bottom of the tank. The temperature at the top and bottom are easy, I will use a couple of DS18B20s strapped to the inlet and outlet pipes. I know this method of measurement is not very accurate, but for my purposes the readings are adequate. The water flow is also easy with a standard pulse output “pelton” wheel.
That only leaves monitoring the gas flow, I suppose I could purchase a flow sensor specifically for natural gas, but I suspect it would be quite expensive.
Since the flow rate is constant I should be able to get a good estimate of the gas usage by timing the on periods of the gas, and using the rated gas usage calculate the actual reading. The question now becomes how do I measure the on time, is the gas control non electronic, the gas is controlled by a temperature sensor in a mechanical method such as has been used for more than 60 years, or is it electronically controlled. Since it has not been installed yet, I have to guess and as the ‘old’ method needs a pilot flame which uses gas 24/7 I don’t expect that will be used any longer so I am expecting an electronic control. I can probably measure the on time by sensing the on time of the gas solenoid which I expect to be 24 Volt AC. that being the case it is easy to rectify and scale the voltage to a value suitable for a microprocessor. If that method is unavailable, I could use an infra-red non contact sensor to detect the flame, however I would lose some accuracy and the cost and complexity would increase.