Pumps for Nozzles and for Liquid Cooling
10.18.04 - Note that one or two pumps are required for the Sola Roof system. One is for providing the liquid to the soap spray nozzle, and the other is used in the dynamic liquid cooling process. One pump may be used for both functions by using appropriate valves, or two pumps may be used if each is dedicated to a single function.- Marcin
Rick uses two pumps - 'I have always used two separate pumps. One reason is that these two processes could be operating at the same time. The other is that the control valving as compared to the pump cost is not much difference. Another is that the pumps can have different specification. However, in general the same model 40 psi, 40 gpm can be used but the pump for the bubble generators could supply a large roof area. Say each bubble generator requires 4gpm to the nozzles then one could use one pump for about 20 units (remember that there is line loss and pressure at the nozzle must be uniform). For the liquid solar process it is good to have pumps in the 1 to 2 Kw power range and have more pump units. This makes the system redundant and reliable and an individual pump is easily replaced. Balancing is never a problem since a single pump 2000 square feet). They are both (relatively) low pressure and high volume supply - so the centrifugal pumps are a good choice.
10.17.04 - I looked over the Dankoff pumps and the one that would be best for the typical Sola Roof is their Sun Centric? centrifugal pump (the picture looks just like the AC pumps from http://www.starite.com/ - look at pool pumps - Dyna-Glas and Dura-Max models) for swimming pool circulation and other high volume low head applications. The spec sheet show 50 gpm at 20 ft lift, which is great and would serve 1000 square feet or more of liquid solar process to establish a good thin film flow of cooling liquid over the inner cover of the building envelope. This will consume about one Kilowatt per hour and would be capturing about 80 Kw of solar thermal gain per hour during the mid day hours - using the entire south facing side of tunnel the size of Ross's greenhouse (during the winter day) or the north facing side during the summer day. See the Summer & Winter slides at http://www.solaroof.org/gallery/seasons
Positive displacement is not necessary for the liquid cooling or bubble generation and takes too much horsepower to make a high pressure low volume flow. There are some fire fighting foam generators that use these pumps and no fan or blower, just the water pressure and a mixing venturi to produce foam like a cannon. But this is a very different type of foam, not high expansion and not capable of flowing like air to fill the channels in the cavity space. It is best to have a lower volume higher pressure (40 psi) centrifugal pump for supply the bubble generators. One pump can supply 4 bubble generator units. One higher volume lower pressure pump (20 psi) for the liquid cooling and one fan or blower motor for each bubble generator. This is not more equipment than is used in a conventional greenhouse to control exhaust fans, window vents opening/closing, curtain operation and the heating system. Remember that these motors can operate 10 to 15 years and the Sola Roof has no other moving parts to wear and tear. Curtains are replaced every 3 to 5 years, windows that open will break sooner or later and furnaces and their fuel and their heat distribution systems are much more complex. Depending on the climate you can save up to 1.5 to 3.00 dollars per square foot per year - about the same as the Sola Roof equipment cost - make the best capital investment and collect all the benefits for years to come. - Rick