Flow Meter

CountryTodd

I'm looking for a flow meter to install in our solar loop. I don't need anything fancy. High temp rating, ideally 3/4" copper connection, low flow (1-4 gpm) scale and ok to use in a glycol system. There must be something better than this

https://www.amazon.com/Hedland-EZ-View-Flowmeter-Polysulfone-Water/dp/B005Q1JS24

This Caleffi flow meter is more in my price range, but I believe that this is designed to attach to a Caleffi manifold so the fitting on one end would be odd. Is there a way to adapt to copper? Also, the temp range isn't listed.

http://www.houseneeds.com/heating/radiant-heat-pex-tubing/dahl-pex-tube-fittings-compression-adapter-flow-meter-34-inch

SWEI

These are frequently used in solar systems and seem to hold up well.

hot_rod

CountryTodd said:

I'm looking for a flow meter to install in our solar loop. I don't need anything fancy. High temp rating, ideally 3/4" copper connection, low flow (1-4 gpm) scale and ok to use in a glycol system. There must be something better than this

https://www.amazon.com/Hedland-EZ-View-Flowmeter-Polysulfone-Water/dp/B005Q1JS24

This Caleffi flow meter is more in my price range, but I believe that this is designed to attach to a Caleffi manifold so the fitting on one end would be odd. Is there a way to adapt to copper? Also, the temp range isn't listed.


Here is the one you are looking for
http://s3.supplyhouse.com/manuals/1300720735365/50941_PROD_FILE.pdf

http://www.houseneeds.com/heating/radiant-heat-pex-tubing/dahl-pex-tube-fittings-compression-adapter-flow-meter-34-inch

Be careful of the temperature range on plastic flowmeters.

SWEI

hot rod said:

Be careful of the temperature range on plastic flowmeters.

Definitely. Polysulfone will hold up, but polypropylene end pieces will soften before that. They make brass ones.

hot_rod

SWEI said:

hot rod said:

Be careful of the temperature range on plastic flowmeters.

Definitely. Polysulfone will hold up, but polypropylene end pieces will soften before that. They make brass ones.

What about glycols in plastic meters, at 250F? Pressure rating also.
I've seen those plastic turn dark amber color where you cannot see the float inside, temperature and fluid perhaps?

Remember flat plate collectors stagnate at well over 325F, evac tubes maybe 500F.

CountryTodd

Brass seems like the best choice but I haven't found one yet.

CountryTodd

http://www.solarpanelsplus.com/pdfs/flow-meters.pdf

Product # NA255110, listed on the site above seems to be a discontinued item but some vendors still list it "in stock".

hot rod and others, what do you think of this option?

SWEI

hot rod said:

What about glycols in plastic meters, at 250F? Pressure rating also.

We use them (and I see them from others) on the supply side of drainback systems. Tank high limit (sensor near the bottom) is at 170°F. If properly placed, they do dual duty as a sightglass. I'd like to find a glass version, but most of those seem to be set up for very low flows.

hot_rod

Yeah, we upgraded that product the correct number is NA223529
NA12259 is the 3/4 sweat tail

Another caution with the plastic versions is on drain back systems you need to install a spacer to prevent the disc from closing off flow, preventing drain back

The Caleffi has a small rotary wheel

Bob Harper

It depends whether you're looking for a flow indicator vs. an actual flow meter as in measuring the flow volume or rate. Then it becomes a matter of accuracy and budget. As stated by Hotrod, the materials must be compatible with the process and conditions of use. You can find cheap meters that may claim accuracy of plus or minus 10% when they really are plus or minus 50%. Until you have a meter that has been calibrated, its really just a glorified flow indicator. This Caleffi states an accuracy of 15% at a flow rate of 1-5 l/min. On the low end, it could read 1L/m when it's actually 0.85 L/m which may be too low to detect. On the top end, you could be off by 3/4ths of a liter either way. Just understand the limitations of your equipment and don't ask them to do what they cannot. If this hysteresis is acceptable that's fine but it is incapable of fine measurement. Another factor rarely mentioned in low end meters is repeatability, which is often more valuable to industrial processes. When it reads say 3 L/m does that rate mean so much specifically or that it serves as a repeatable reference number to balance against other zones? That's the question.

CountryTodd

Sounds like the classic case of getting what you pay for.

matt_sunwaysolar

These are the ones I use:

http://www.caleffi.com/usa/en-us/catalogue/quicksettertm-balancing-valve-132432a

Price is a little higher and you have to pull the pin to register the flow rate, but pretty accurate and haven't had any issues in the field, with probably 50 or so installed. They are brass and can be used with drainbacks.

The problem with the Caleffi's with the rotary wheel is that there are a lot of failure points. I've had the springs dislodge, the float get stuck(up or down), the float crack and the whole mechanism get clogged with debris that made its way in. Especially on a glycol loop, not something that you want to be servicing much. I've had similar issues with a few of the Blue-White's too.

Additionally, plastic threads are pretty easy to crack or cross, so not my preference.

SWEI

Matt, I assume these are being installed on the return line? Looks like a nice unit, and I like that they come with an insulation shell.

The downside for me is that now I need a separate sight glass. I'd prefer to keep that inline to minimize complexity and potential failure points. Is anyone aware of a source for a section of glass pipe with fittings?

matt_sunwaysolar

SWEI- Yes, the line returning to the collectors.

We use Apollo sight glass fittings, but get them from HTP (formerly Solar Skies) with their DB units. I've looked to source them independently, but they're fairly expensive solo. As far as sight glasses themselves, HVAC/boiler supply houses should have everything (likely including the fittings).

SWEI

Perhaps I'm just a bit dense, but 'returning to' seems like it could mean what I would call the supply (cold) side. I like to see a globe valve in the hot (collector output) side line just above the tank for throttling.

Working on a new single tank design here, so the 'sight glass' needs to be in the supply riser above the pump, parallel to and near the top of the tank.

hot_rod

SWEI said:

Perhaps I'm just a bit dense, but 'returning to' seems like it could mean what I would call the supply (cold) side. I like to see a globe valve in the hot (collector output) side line just above the tank for throttling.

Working on a new single tank design here, so the 'sight glass' needs to be in the supply riser above the pump, parallel to and near the top of the tank.

http://www.supplyhouse.com/pex/control/search?SEARCH_STRING=gauge+glass

I think there is a company on Long Island, NY that makes the site glass packages too.

Knowing that it all gets fairly dirty or foggy I use Uponor pex.
I think HTP uses some sort of plastic with a crimp fitting on their newest version DB tanks.

It depends on the diameter of the tank or drainback as to how long of a site tube you need. A tall skinny tank might need 12" or more to watch the fluid level from cold, to highest temperature.

Also the volume, with my 500 gallon tank, you need quite a large expansion space.

SWEI

The design is for a system which will be certified and sold, so I don't think PEX will fly. I'm leaning towards a foot of polysulfone pipe at this point.

hot_rod

SWEI said:

The design is for a system which will be certified and sold, so I don't think PEX will fly. I'm leaning towards a foot of polysulfone pipe at this point.

Select plastics carefully to be sure it is compatible with common fluids. Glycols and alcohol find their way into drainbacks and some of the new solar fluids are bio based.
http://www.rtpcompany.com/technical-info/chemical-resistance/

matt_sunwaysolar

HTP is still using the PEX tubes, which in my opinion and experience, is a bad choice. The expansion factor of PEX is way too high for the temperature differential. They turn to spaghetti and look awful. That's best case; worst they expand themselves out of the compression fitting/ gasket they come with. I've even had the pump on the other side of an HX fail, letting the solar side get so hot (from lack of heat transfer) that the PEX tube burst. We lost most of the glycol, luckily the pump didn't burn out.

I only use glass. AET's polycarbonate also discoloration heavily and can crack from excessive heat.

Glass has been pretty fail-safe for me. Doesn't expand or contract much, doesn't discolor, doesn't crack (short of heavy impact, which I've never actually experienced). Not very expensive either.

In standard HVAC-speak, the "supply" refers to the side delivering heat, while the "return" refers to the side going back to be heated after delivering heat. Kind of backwards for solar thermal thinking, but collectors are a boiler.

SWEI

I'd prefer glass. I'm going to see if I can find straight, valveless fittings from one of the sight glass makers.

If I'm going to combine the flow meter and flow restriction point, it needs to be on the hot side, just above the tank.

matt_sunwaysolar

Any reason not to do the site glass on or near the vessel itself? And won't you need it to be "side-arm" or "t'd off" of the main loop piping? (Otherwise, it's just a pipe length, which should be full during operation.?)

The Caleffi unit that I linked has a circuit-setting valve as well, so that it can throttle flow. That way, you could save a valve?

Any reason in particular you're putting it on the hot side? Is there any fear that too much restriction on the suction-side may cause pump cavitation upon start up?

hot_rod

SWEI said:

I'd prefer glass. I'm going to see if I can find straight, valveless fittings from one of the sight glass makers.

If I'm going to combine the flow meter and flow restriction point, it needs to be on the hot side, just above the tank.

Glass sounds like the best option. You may want to remove and package that glass tube separately for shipping. It is very breakable when mounted on or along a tank or pump station.

On a few DB I just block open the 132 pull ring so it always reads flow at a glance. Cut a piece of 1/4 copper tube and squeeze it around the stem when the ring is pulled out.

The valve function would make this a balance valve, isolation valve and flowmeter all in one. We also have a temperature gauge adapter for it.






I think those sight glass fittings are just compression ells with o-rings instead of the brass ferrule.

http://www.bargainfittings.com/index.php?route=information/information&information_id=9

SWEI

Dale Pickard turned me on to the idea of using one size smaller pipe on the collector hot line (he calls it the downcomer) to help the pump maintain positive pressure at the top of the loop. I've tried it and it works quite well on larger arrays. Systems with under 100 ft² of collector area require larger piping than would be dictated by flow velocity calculations in order to ensure reliable drainback. The HTF has a tendency to 'rain' on the downhill side, leaving zero pressure at the top of the collectors. We started adding a globe valve on the hot line just above the tank to regulate flow in place of the ball valve typically installed on the pump outlet. The result is a faster system fill in the AM (air goes through a choked valve far faster than water does) and no more 'raining' noises. A Caleffi 132 in place of the globe valve would take care of two of the functions, but we still need a way to set and monitor the fill level. A sidearm-style sight glass adds cost, fittings, and potential failure points. A variable area flowmeter (e.g. Blue-White, Pentair) installed on the cold riser above the pump provides the sight glass function so we need to replace that if we move to a 132 on the hot return.

Iconprocontrols

I would suggest you to try these peddlewheel flowmeters work really well, I have tried them in our firm.

EBEBRATT-Ed

Just an Idea.

Pipe the flow meter in with a 3 valve bypass with a drain. Then you can "put it in the system" when you want and "drain it" when you don't.

Then the flow meter and it's construction are less important