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

This picture is from a youthful man who grew up along with his dad being a heating contractor, like so many guys within the enterprise. He asks a whole lot of questions, which I believe 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.

Once I was new within the enterprise, I wouldn’t at all times ask questions. I believe the explanation was to not appear to be I didn’t know the reply already. I believe I’ve gotten over that unhealthy conduct through the years. I encourage you to ask inquiries to be sure to perceive that idea or prompt piping diagram. A greater understanding of what you’re engaged on leads to higher work.

Two Pump Downside

He wished to know if “you get twice the movement out of those pumps or identical movement 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 movement charge stays primarily the identical. If the pumps are the identical dimension, the movement stays the identical if one pump or each pumps are operating when piped in sequence.

If the pumps are piped in parallel, aspect by aspect, then the movement charge will increase to primarily the full of what number of pumps are operating. If the identical dimension, you possibly can assume that the movement charge 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. Truly it’s primarily the identical movement charge however at near double the top fairly than at a decrease head. Once more, the engineers of the world will have the ability to calculate that extra precisely. The rule of thumb is, pumps in sequence double the top with movement remaining the identical, whereas pumps in parallel double the movement with head remaining the identical.

Max Scores

I texted again, “identical movement and nearly double the top of 1 pump”. He then acknowledged that one pump is rated for 17.6 gallons per minute at 15.4 ft of head, so these pumps in sequence would produce 17.6 gallons per minute at 30.8 ft of head. Realizing that this mini-pump wasn’t able to that form of efficiency, I instructed 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 have been right, however pumps don’t function at their max scores. They function at someplace in between the max scores, the place the movement charge is restricted by the top of the system.

You would possibly get near 17.6 gallons per minute if the top of the piping is about zero, otherwise you would possibly get 15.4 ft of head if the gallons per minute is about zero. Zero doesn’t occur in closed loop hydronic programs. As soon as the pump is energized, water begins transferring and the system head is shortly created by the friction of the water transferring by 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 programs have little or no head loss due to over-sized pipes, like 100-plus-years-old gravity sizzling water programs. Some programs 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 carried out.” I largely see pumps in sequence on geothermal jobs. However the image seems like a radiant flooring job, which might even have larger head due to under-sized PEX tubing or unusually lengthy loop lengths. The reason being larger head at decrease movement charge, which might be dictated by design.

My reply was “two pumps are cheaper than one pump on the identical obligation level.” That’s what I used to be at all times instructed and the price of items is a robust driver on this business. If it’s cheaper to bolt two pumps collectively than the value of 1 pump, then any individual’s going to do it. The water transferring round doesn’t care.

We then moved on to sizing a pump, “must feed a sizzling water coil with little head loss, round 50k btu.” I do know from expertise {that a} typical mini-pump—select your favourite taste—will do exactly tremendous for that kind utility. You’ll be able to assume about 5 gpm for the movement from the btus and perhaps 5 ft 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 medical points.