Coffee with Caleffi: Hydronic Piping Systems – Proven Designs (Part 1)

Mechanical engineer leads technical webinar for plumbing contractors, designers and wholesalers.
Coffee with Caleffi: Hydronic Piping Systems – Proven Designs (Part 1)

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John Siegenthaler, mechanical engineer with Caleffi Hydronic Solutions, leads an online webinar “Part 1: Hydronic Piping Systems – Proven Designs,” from noon to 1 p.m. CT on Thursday, Sept. 22.

He will examine the basic approaches and discuss how they should be selected based on factors such as heat source, zoning, thermal mass of the heat emitters and type of piping used.

There is no cost for the complimentary education series, Coffee with Caleffi, but registration is required.

Topics include:

  • Proven approaches that will yield consistent performance
  • The correct way to pipe a hydronic distribution system

The following is a Q&A from last month’s webinar, “Pumped Glycol vs. Drainback Revisited,” led by Bob “Hot Rod” Rohr, Caleffi training and education manager.

Q: Isn’t deionized or demineralized water more aggressive as it’s stripped of all minerals that make it attack copper system components?

A: You are correct that purifying water can also create more aggressive water. We suggest between 10-30 on the TDS meter at the top of our Hydrofill when filling. As Mark mentioned, the metals in the system will buffer that filtered water to a safe level.

I am a fan of using hydronic conditioning additives; Rhomar 922 is one example. These will buffer pH, lock up some hardness, scavenge O2 and provide a film coating inside the pipes and components. They should be added to good-quality water however, or you compromise the inhibitors from day one. These are basically the same inhibitors that are added to solar and hydronic glycols. Just add them to the water when filling. Most manufacturers offer spray aerosol cans that treat about 35 gallons of fluid — very user-friendly.

You are wise to question water quality. This has become a big concern in the solar and hydronic world. Failed copper or braze joints can often be traced to water quality. A few basic tests will steer you to the need to filter your water or not. A pH and TDS meter will tell you a lot.

Q: For the modulation of the pump of the iSolar controller, does the pump have to be particular to this setup or will a standard pump/circulator work? I assume the controller’s Triac will not act as speed control for a Grundfos Alpha Circulator?

A: Yes. Any typical PSC type circ pump can be operated via the Triac relay. We have used both Wilo and Grundfos brands in the pump stations.

It is also correct that an Alpha or other ECM cannot run via the Triac output. If you can find an ECM with a PWM input, the iSolar control lets you select Grundfos, Laing or Wilo. Find this selection in the Pump Control parameter. Rumor has it we may see small PWM, ECM circs soon. They exist in Europe already, but in non-UL, 230V versions.

I have tested the Grundfos PWM ECM solar pumps with the Caleffi controls, they work fine together.

Q: On the one tank drainback, doesn’t the collector have to drain back into the air space? You have it shown at the liquid level. If the pump turns off, doesn’t the collector have to be able to drain back and have an air gap?

A: I believe Apricus had a DB tube system on the market called the Wombat (I think). I don’t have any experience with that model. I tried both heat pipe and U-tube style in drainback applications without much luck. I do have an Oventop tube array (heat-pipe-style evac tube) on my house as a DB and I just put glycol in it. I test that fluid from time to time to see how it is getting along, as not 100 percent drains back.

No air gap or vacuum breaker needed on a properly installed DB. When the pump stops, that air bubble rises up the one side and “breaks the siphon,” allowing drainback. Now, some installers add a small copper tube into that air space to ensure the air bubble can get into the piping. Some of our drawings show that detail. Personally, I have never added that additional line and so far, no problems.

Q: Why do you need check valves on both supply and return piping rather than just one?

A: It is possible to get some ghost flow with check protection on just one of the lines to the collector. Hot and cold water can flow in two directions inside a pipe under the right conditions. We learned this with primary secondary piping via closely spaced tees. If the piping was vertical from those tees, thermosiphoning was possible. A single check did not always stop that 100 percent, nor did thermal drops.

Our European partners that developed our solar pumping stations were insistent that two “gravity gates” be used — one in supply, one in return. With that in mind, they developed that check/ball valve with a mechanism to force open the check, or allow flow past it in a 45 position.

The Germans use one method where the edge of the ball lifts the check. The Italians found another approach to the manual check opening function by milling the edges of the ball. We show our version on slide 15.

Q: Who makes a high-head, low gpm variable-speed pump that is 120-volt? Can the drainback feature on the iSolar controller be used with a non-variable-speed pump?

A: I’ve found the Grundfos 15-100 3-speed fits most systems up to maybe three or four collectors, 4-5 gpm sized arrays. At 1.1A, it can be run as a VS from the iSolar controllers.

Yes, the DB function can be used with any common pump with a 1 amp or lower rating. We offer the Grundfos UP15-100, Wilo Star S-16 and Wilo Star S-21.

Q: Do you add both the pressure drop through the piping and the elevation to size the booster pump?

A: Yes. I would consider that pressure drop, especially the installers that are using the corrugated stainless tubing that has some high-pressure drop potential.

Q: When using two pumps, booster and variable speed, is the booster pump always first in line?

A: Our iSolar controllers only have two options from drainback mode. One pump with variable speed or two pumps in fixed speed for both. If you had a control, that could run the booster at full speed, then the operating pump on a VS function, which would be nice. I would still have the operating pump below and pumping through the booster pump.

Q: Wouldn’t having the booster pulling through the variable-speed pump even cause more cavitation for the booster pump?

A: I have been taught by the pump people to avoid any pressure drop devices on the suction side of a pump or circulator. Usually on a two-pump system they are fairly low-head circs, but it is still a best practices approach, IMO. Certainly with high-head, higher rpm circs, cavitation potential could increase. I prefer to pump through the un-powered pump regardless of the size or speed of the pump(s).

See the webinar:


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