Simple Hydronics Question with a Lot to Unpack: Why Two Pumps?

This photograph is from a youthful man who grew up together with his dad being a heating contractor, like so many guys within the enterprise. He asks numerous questions, which I feel is nice. He has a pure curiosity, which he may need gotten from his father. He additionally isn’t afraid to ask questions, which I additionally assume is nice.

After I was new within the enterprise, I wouldn’t all the time ask questions. I feel the rationale was to not seem like I didn’t know the reply already. I feel I’ve gotten over that unhealthy habits over time. I encourage you to ask inquiries to be sure to perceive that idea or urged piping diagram. A greater understanding of what you’re engaged on ends in higher work.

Two Pump Downside

He needed to know if “you get twice the stream out of those pumps or similar stream at decrease head?” What you see are two pumps flanged collectively so one pump discharges immediately into the opposite. Within the commerce, it’s known as pumped in sequence.

To reply the primary a part of his query, No. The gallons per minute stream fee stays basically the identical. If the pumps are the identical dimension, the stream stays the identical if one pump or each pumps are operating when piped in sequence.

If the pumps are piped in parallel, facet by facet, then the stream fee will increase to basically the overall of what number of pumps are operating. If the identical dimension, you possibly can assume that the stream fee doubles (though the engineers of the world will in all probability say one thing else, however very near double).

To reply the second a part of his query, No. Really it’s basically the identical stream fee however at near double the pinnacle fairly than at a decrease head. Once more, the engineers of the world will be capable of calculate that extra precisely. The rule of thumb is, pumps in sequence double the pinnacle with stream remaining the identical, whereas pumps in parallel double the stream with head remaining the identical.

Max Rankings

I texted again, “similar stream and virtually double the pinnacle of 1 pump”. He then acknowledged that one pump is rated for 17.6 gallons per minute at 15.4 toes of head, so these pumps in sequence would produce 17.6 gallons per minute at 30.8 toes of head. Realizing that this mini-pump wasn’t able to that form of efficiency, I advised him that he is perhaps studying the curve incorrectly.

He replied “that’s what that pump was rated for on the max.” Now I knew the place he had gotten off monitor. The max scores for the pump had been appropriate, however pumps don’t function at their max scores. They function at someplace in between the max scores, the place the stream fee is restricted by the pinnacle of the system.

You would possibly get near 17.6 gallons per minute if the pinnacle of the piping is about zero, otherwise you would possibly get 15.4 toes of head if the gallons per minute is about zero. Zero doesn’t occur in closed loop hydronic techniques. As soon as the pump is energized, water begins shifting and the system head is rapidly created by the friction of the water shifting by means of the pipes.

The extra gallons per minute in the identical dimension pipe creates extra head. The opposite a part of the pump head query is the size of the pipe. Once more, the longer the size, the extra head it creates. The reference I take advantage of for these calculations is the B&G System Sizer. Some techniques have little or no head loss due to over-sized pipes, like 100-plus-years-old gravity scorching water techniques. Some techniques have very excessive head loss due to lengthy piping runs, like fashionable geothermal loop fields.

The Water Does not Care

His subsequent reply was “by no means knew why that was finished.” I principally see pumps in sequence on geothermal jobs. However the image seems like a radiant flooring job, which may even have larger head due to under-sized PEX tubing or unusually lengthy loop lengths. The reason being larger head at decrease stream fee, which will be dictated by design.

My reply was “two pumps are cheaper than one pump on the similar responsibility level.” That’s what I used to be all the time advised and the price of items is a strong driver on this business. If it’s cheaper to bolt two pumps collectively than the value of 1 pump, then any person’s going to do it. The water shifting round doesn’t care.

We then moved on to sizing a pump, “need to feed a scorching water coil with little head loss, round 50k btu.” I do know from expertise {that a} typical mini-pump—select your favourite taste—will just do high-quality for that sort utility. You may assume about 5 gpm for the stream from the btus and possibly 5 toes of head from his description. That hits the curve completely on the low velocity of the mini-pump that we inventory.

Replace

For these of you monitoring my well being, I’ll report that chemo is a problem and I can’t wait till it’s over. I now have a greater perspective of individuals struggling by means of medical points.