Commercial sized solar thermal installations can seem rare at times in our area.  However, when they do occur contractors, wholesalers and yes even engineers accustomed to residential installations can run into serious  but common stumbling blocks late in the game which can result in costly change orders and delays. Here are two that have come up on my recent consultation ventures.

Inadequate Pumping Power: 

With multiple banks of collectors, reverse return piping on the roof, and manifolded storage tanks piping distance can quickly add up. Two banks of five collectors can result in between 140 to 310 feet of copper and solar manifolds before you even get down through the roof! At a minimum flow rate of 7.5 GPM with a 50% glycol mixture frictional resistance could well exceed 25-35 head/ft by the time we factor in piping to the mechanical room and solar tank coils. Cold morning startups will certainly provide a workout for even adequately sized pumps.

A lot of us may flip through a manufacturer’s catalog and find a commercial pump station with a pump capable of 10 GPM or 30ft of head. In a rush we could look at this and estimate that this will get the job done, before we actually plan the piping runs and quickly forget about it until it’s piped in the system. “Hey it can move 8.5 GPM and the collectors are only 16 feet above the pump it could work right?” Not really.  If we take the time to actually calculate head loss and look at the pump curve these “commercial” pump stations might be able to do 4-6GPM once the system has warmed up on a system similar to the one described above, early morning startups aside.

Let’s just get this fact out there, most pre-engineered and factory assembled “commercial“ pump stations are more accurately described as heavy duty residential pump stations. If we are designing a system that has more than 5 collectors we have to assume that all the mechanicals will be site assembled from hand-picked equipment that we size ourselves, pumps, air scrubbers, isolation valves, temp gauges and more, some of which will not be regularly stocked items resulting in costly delays and pricey shipping bills.

Bottom line, know how to calculate pressure drop and read a pump curve, its basic knowledge and readily available online. Guesswork just doesn’t cut it.

Here is another issue that can catch anybody off guard.

Mismatched Controls:

I think a lot of us have wised up over the past few years to the fact that we need a control with the correct number of relays and triacs to control all of our systems functions, pumping speed, diverting etc. Heck, we don’t even stock controls that don’t have variable speed at here at T.P.! They are a thing of the past if you ask me. Yes, we all have learned to at least check that relays equal number of motors we are powering, but are the relays rated to do the job?

Well, for commercial systems probably not. Our go to control, the iSolar Plus, can do most every function we want for a residential or commercial solar system save a few specialized functions that the new BX control will handle. But if we look at the specs the iSolar Plus has 1 amp relays, which are fine for our standard small circulators that run between 60-90 watts. Did you know the “commercial” pumps draw 170 watts on high speed? Not a good combo for an iSolar Plus with a 1 amp relay and a 120V wall socket (as an update we have checked on this issue and come up with some reassuring answers, but this is still a good lesson for any professional).

This is another case where our familiarity with residential systems lulls us to sleep. Any one of us could easily fall into the trap where we smartly remember that we need a diverter valve in the system and say “hey we need an iSolar Plus on arrangement blah, blah, blah, to handle that if we want heat dumping as well! Good catch me.” (Pat self on back).  We order the bigger pump station made by the same manufacturer we always use and assume they will work together and no one is the wiser until you try to commission the system and it doesn’t work the way we thought it would. This means change order time and hopefully the customer isn’t around to watch us scratch our heads while we look like amateurs trying to figure out the issue.

The moral of this post is to read product literature, check your pump curve and work with people who you trust to know what they are talking about. Here at Thermal Products we’re not always perfect but we focus on the details and work to help you through the design process on every system so you can avoid costly and silly mistakes like these.

Remember 1 quality installation serves your business better than 10 mediocre ones! Help give solar thermal a good name.

John Ginda

Outside Sales/Solar Training/Consulting

Thermal Products Inc.