Saturday, January 2, 2010

Project #1 - programmable thermostat

My first project is a programmable thermostat for a boiler mounted in my apartment. In a town where I live there is a small CHP power station (combined heat and power). It was built long ago to support the industry with hot water for technical processes, and actually generates very little electricity (6MW in winter, during other seasons even less). The station supplies almost all apartment and commercial buildings in the area with hot water for heating and washing purposes. My building is probably the only exception. Such solution is both blessing and curse, as it gives me better control over heating, but is not forgiving of any mistakes ($$$).

The boiler is 24kW Nike Mini from Italian company Immergas, not the latest model, but still quite new. It is a combi-boiler - it produces hot water for both heating and domestic uses. The boiler can be set to provide domestic water only, or both heating and domestic water. Domestic water flows through heat exchanger and then directly to taps. Water for heating flows in a closed circuit and it's moved by electrical pump. The temperature of the heating water is measured by a sensor, and when it's too low, the boiler ignites itself and works for some time (it's either fixed time or until the temperature raises to acceptable value - I don't know).

The problem is that the boiler doesn't measure the temperature inside the apartment, so it doesn't switch off even if the temperature reaches preferred value. It also has no means of time-related programming, so it runs all the time, even when nobody's home. That's why the programmable thermostat is necessary. This device switches the boiler on only when the current temperature in the apartment (precisely in one of the rooms) is lower than value set in thermostat's memory.

Of course Immergas sells all kinds of thermostats for its boilers. Small electronic companies and workshops also sell thermostats which can easily be adapted to control my boiler. But by making it I hope to learn some new skills and test some solutions which might be useful later.

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