SWIM PC AUTOMATION and MONITORING
CANADIAN RESEARCH and DEVELOPMENT ACTIVITIES
Multi Family Solar Hot Water Preheat in Surrey BC
This solar water heater consists of 18) 4x10 boxed and glazed solar collectors all plumbed to a 1000 gallon open vented tank in the basement. Heat exchange from this solar heated tank to the cold water on its way to the hot water tanks are coils of 3/4" copper pipe immersed inside the tank.
The system was installed by Renew Energy in 2010 but not completely. As usual, the controls were tied into the building's automation system. A controls programmer or a mechancial engineer came up with a solar control algorithm that was entered into the DDC and never checked or looked at again. Three years later the owner contacted Renew Energy for a system check up and what is discovered is that the system is not operational and may have never operated. This kind of story is very very common with solar systems installed as part of Canada's Eco Energy Program. There was no monitoring and the idea of long term commissioning doesn't fit well with construction law in general. Everything needs to be signed off as fully complete before payment is issued. Monitoring and a longer term commissioning are unique requirements of any clean tech initiative.
Renew had no access to trend logs from the building automation system so they installed a SWIM PC solar hot water system controller from Hot Sun. They bypassed the existing ddc control system and ran solar on the Hot Sun controller and monitored the data. They found that there was a high water load at this facility. The solar panels heated the tank right up to set point on sunny days and the entire 1000 gallons of hot water got fully consumed every day.
One issue discovered through proper online monitoring was with the solar sensor. Boxed and glazed collectors have a well inside the box of the collector between the copper grid and the glass. It has always been thought that this temperature was well above the collector temperature and a solar differential setting of something like 18F was used. That solar differential means the collector has to be 18 degrees warmer than the tank for solar to be on. What our monitoring demonstrated was that the collector quickly cools to just a degree or two above tank temperature. Solar stops and the solar panel then heats up again. Then solar is on then off then on as seen in the monitored data above for Oct 24, 2013. Our monitoring is calculating the energy based on the difference in temperature into the collectors vs out assuming flow is constant over 3 minute intervals so our energy data is meaningless. It is also not efficient and not good for equipment to be cycling. It is far better that solar stays on when it can add heat to the tank. The remedy in this case is to change the solar differential to 1 and 0.5 so that solar turns on when the collector is 1 degree above the tank and solar shuts off (the solar off differential) when the solar temperature is only 0.5 degrees above tank temperature. Most solar controllers for hot water systems have factory set differentials or adjustable ones that don't go down low enough to eliminate this cycling. Could it be that there are billions of dollars worth of solar hot water systems all operating on the wrong solar differentials?
The moral of the story is you have to monitor solar thermal systems. Here we are 3 years after installation trying to properly commission the system for the first time. Give the solar company the controls part of the job along with the plumbing. Building automation may be a major committment on the part of a new building but that doesn't mean it has to control everything. It has limitations and this is one of them. This is why Hot Sun developed our own monitoring equipment.
This size installation can be done for about $40,000 The expected energy delivery on an appropriate load should be in the neighborhood of 200 GJ. This needs to be confirmed with our data over time. That's hopefully a cost of equipment to annual energy delivery ratio of $0.72/kwhr making this particular installation potentially viable. Stay tuned.