I read an interesting article recently about how to calculate the size of an on-demand hot water heater.  OK, while not exactly what most people would consider light reading, what I thought was interesting was how much energy it takes to generate something we take for granted.  The article discussed how running a single shower would require the incoming water to absorb energy at a rate of about 75,000 BTUs per hour and that if the tankless water heater was 80% efficient, then the heater would need to have a rated input of 94,000 BTUs per hour.  If you want the ability to run two showers simultaneously, then the numbers double so that the tankless water heater would have a rating of 188,000 BTU.  (For reference, the boiler I have for heating my house and domestic hot water can modulate  read more... »

The Mill Creek NetZero Home (MCNZH) will collect solar energy in three different ways: using passive solar design, using photovoltaic (PV) modules, and using solar hot water (SHW) collectors. The SHW collectors are the ones that heat water - they are the black ones at the top of the above picture.

According to a recent article in Home Power magazine (Oct/Nov 2008, p.40), SHW collector efficiency is 50%-70%. That's pretty good when you consider that the best PV module is about 17% efficient.

I've been contemplating the design of the MCNZH's SHW system for months now. The pieces started to fall into place once the federal government released a crucial tool: The  WATSUN 2008 SHW System Simulator.  read more... »