- Thermal Audit
Taco Solar X-Pump Block
This was originally in the solar install page, but was moved out now that it has been recommissioned as a heat dump to the floor heating system.
A Taco solar X-Pump block (two pumps, a heat exchanger and electronic controls) was used to transfer heat from the collector to the storage tank above, not using the in-tank coil, and it did simplify the installation. However, this system has now been relegated to transfer heat to the floor heating system. The x-pump block wasn't doing well at efficiently transferring heat on dull days and it appears that the RESOL brand controller operating a pump and in tank coil (located at the bottom of the tank where it is coolest) was about 10% more efficient. I might have spent more time trying to optimize it but Taco's product managers did not return my numerous queries and the flow meter option they advertised is not available nor is it possible to interface with the unit electronically.
The Taco unit was easy to set up and works out of the box without changing any settings. It needs a minimum of two temperature sensors; the storage tank sensor and the solar collector output. The thermisters are connected with low voltage 18 gage wire designed for thermostats. There is a hole in the solar manifold for a temperature probe (see photo below) but it was too small for the Taco supplied thermisters, so the thermister was tie wrapped to the brass union and covered with pipe insulation. This mounting position underestimates the manifold temperature by about 4 degrees when the pump is not running, but is adequate to guide the pump controller. Once the pump is running, the error is smaller.
Inside the pump, the wires are simply screwed to the terminal block on the bottom of the image shown below. This is the back of the black colored module containing the LCD readout that you can see in the complete picture of the Taco pump block above.
The back of the Taco SXPB-1 contains the heat exchanger.
The Taco x-pump block consumes about 0.73 kWh on a sunny day when measured with a kWh meter over the run of the sunlit period. Solar storage on such a day (based on Sept 17, 2009) was 23,394,667 J or 6.5 kWh. Therefore, pumping overhead is .73 / 6.5 or about 11%. We chose not to insulate the pumps because they run very hot and we didn't want to overheat them. Since the heat is useful when installed in conditioned space of a house (e.g. a heated basement), it is not really a waste but does complicate being self sufficient. The total annual cost would appear to be about .72 kWh * 365 * $0.12/kWh or $31 at current electric rates. Adding a second panel would not have added additional pumping costs and would reduce the relative overhead.
See the article "Solar Hot Water - Economic Viability on the Canadian East Coast" for more.