quote" Can I run my pool heater with the pump on low speed? "quote

If the pressure switch in your heater recognizes the flow it will work. You'll actually find that you get better heat transfer if the heater will work on the low pump speed.

quote" Will this make the heater less efficient and or damage the heater? "quote

Not at all.

See ya,
Kelly

Yep, if the pressure switch gives the green light to the ignition control, you're good....

Keep in mind, if you are dialed too low in terms of flow, hard to imagine with Hayward 4015, the heater may cycle off as the flow fluctuates or the filter gets dirty....

Quote "You'll actually find that you get better heat transfer if the heater will work on the low pump speed."

This is actually incorrect. Heat transfer is greater when there is a bigger difference between the heat of the flame, and the temperature of the heat exchanger. This happens when the water is moving fast.

brandon - I am not familiar with that heater, but if it gives the option of bumping up to high speed automatically when the heater cycles on, that is the perfect setting to use. The pump can save money running on low speed for most of the time, and then bump up to high speed and get more efficiency out of the heater when it is needed.

quote, I am not familiar with that heater

How can one make a statement about a pool heater that is as common as water in a pool as far as this industry goes and then make any difinitive statement about said heater?

In a sealed combustion chamber such as the StaRite, you are highly vulnerable to condensation. Condensation occurs from excessive water flow as the transfer does not happen. As with every heater there is a desired temperature rise. On average, 13-15 degrees and a desired flow rate, usually 30gpm. At these levels, the heater works excellent and transfer may not be as good for the heater in terms of sooting potential, but it is certainly faster. With a Northstar pump that is fully capable (depending on this installation) of delivering flow rates in excess of the heater design, it seems obvious that higher flow may not be the best option. When the heater senses the excessive flow, the internal bypass (put there for this purpose) will open and allow efficiency to take place at the lower design flow rate.

Put you finger on top of the stove. Does it hurt more if you hold it there or touch and release real fast?

The 400k StaRite heater has a minimum flow rate of 40gpm, and a max of 120gpm. There is no temperature rise listed in the manual. (For comparison, the 400k Jandy LJ heater wants between 30 and 125gpm with a temp rise of 30-39 degrees F. Remember that temperature needs to be measured in the manifold, before the internal cold-water mixing happens.)

The 1.5 hp Northstar pump has a flow rate on HIGH speed of between 108 and 43gpm depending on the total head of the plumbing. They have no ratings published for the LOW speed though. (Is it half of the HIGH speed ratings, or 2/3, or 3/4? Anyone have an idea?)

So it is entirely possible that the low speed flow rate is too low for the heater. However, if this is the case, the heater will shut down on over-temp protection to prevent damage. You still don't want to be bouncing off of the over-temp limit constantly though - this is bad for the heater over time.

The best flow rate for efficiency is to be just over the point where the internal bypass opens. But the only people that know that number are the engineers at Sta-Rite.

repair_guy - at the beginning of your paragraph, you say you have to be careful of condensation with too high of a flow rate, but then at the end the paragraph, you say that the internal bypass will allow the excess flow to bypass the heat exchanger and operate correctly. So which one is it?

That condensation will occur way before 125gpm. Kind of like the same way a heater will burn down way before 150 on the high limit. And, we all know the governor on that flow valve is always corroded or rusty on that heater or any Raypak for that matter.

The comment originally addressed heat transfer. Heat transfer will certainly be great at low speed but at the same time it may not be good for the heater. With the StaRite heater having an optimal flow rate of 80gpm, that too is odd as I know of no pool built that runs optimally at that rate unless it is on 3" plumbing.

"The 1.5 hp Northstar pump has a flow rate on HIGH speed of between 108 and 43gpm depending on the total head of the plumbing. They have no ratings published for the LOW speed though. (Is it half of the HIGH speed ratings, or 2/3, or 3/4? Anyone have an idea?)"

1/2 the rpm = 1/2 the flow, 1/4 the head and 1/8 the power.

I would advise on running the pump on high speed while the heater is running. A heater requires 10 GPM for every 100K of BTUs.

A 1.5hp pump typically runs at 3/16 if an HP at 1725RPM. The max of the pump curve is 60gpm@10' of TDH. To get 40gpm with this system you would need to have less than 20' of TDH which at this flowrate through a 2" pipe is certainely feasible, but not realiable. As the strainer baskets clog and the filter soils it may be very hard so satisfy the flow rate required for the heater (and this is at the low end of the scale). On high speed you know that you will always be able to achieve sufficient water flow through the system. The energy costs are not going to be that much more and the high speed will help with circualation and skimming action with the extra boost in water flow.

Relying on the saftey switches to compensate for bad design is never a good idea.

A closed pressure switch is not a good indicator of whether or not a heater is recieving sufficient flow. These are typically set to turn on at 1 psi.

"The best flow rate for efficiency is to be just over the point where the internal bypass opens. But the only people that know that number are the engineers at Sta-Rite."

The Sta-rite heater has a built in flow control that works similar to rakpak's unitherm governor. It opens as the temperature rises inside of the exchanger. The reason for this flow control isnt for efficiency, it to help reduce the condensation on the heat exchanger.

There really is no hard data in relation for efficiency pertaining to flowrates that I have ever seen.

The only way to know how effective you heat recovery is to compare the flue gas temperature to the ambient air temperature. Remembering that the greater the heat recovery the more condensation will occur. A temp rise test will only tell you if the water is moving through the heater properly, but tells you nothing about how many BTU"s are getting transfered into the water.

I have a question relating to flow IÂll have a heat pump heater. I am interested in the meaning of this statement:
"1/2 the rpm = 1/2 the flow, 1/4 the head and 1/8 the power."

Assume my pool has 35,000 gallons, and a Total Head of 60 feet. Also assume that I have a Pentair WhisperFlo 2 HP 2-speed Full-Rated pump (WFDS-8). Max pump flow is about 100 GPM at that Head. But the pump can turn the water once every 8.3 hours or so since the 2" piping has a max flow of about 72 GPM.

Now, If I operate the pump in Lo speed (1/2 the RPM), 1/2 the flow will be 1/2 of 100 GPM (or 50 GPM). And the pump will consume 1/8 the power compared to Hi speed. So, does this also mean that the Total Head, as seen by the pump, is 1/4 of 60 (or 20)?

I am just trying to understand if a 2-speed pump has the guts to turn the pool water (in this case, 35000 gallons) in 12 hours while in Lo speed.

ThanksÂ
-Gorilla

Guess my math was incorrect... a properly plumbed pool will have multiple lines to/from pool, so there is no limit of 72 GPM like I stated above.

Still curious if the rest of my rationale is correct.

-Gorilla.

I think I have it figured out... 12 hours equates to just under 50 GPM for a 1 turn rate... the 2-Speed pump (WFDS-6 or WFDS-8) can hit 100 GPM at 60 feet TDH on Hi speed, and about 50 GPM on Lo speed. I aswered my own question on the TDH being 1/4 on Lo speed (Hey, I am learning!!)

So it looks like after adding a heat pump, whether on Hi or Lo speed, they'll be no issues (assuming I have no more than 60 feet TDH).

Respond to my post if you think I missed anything.

-Gorilla

Wait I am confused are you putting a heat pump to run w/ the 400K heater? You want all of this to work on low speed?

Racket,

I may have hijacked brandon4589's thread. If your question was addressed to me, then I plan to install only a heat pump... no other heaters for me.

It seems like if I could get 50 GPM on lo speed (and it's theory for now since I did not build my pool), then that would be sufficient flow for a heat pump (the one I am looking at has a minimum flow of 40 GPM).

-Gorilla

One thing you have to be very careful of when dealing with 2 speed pumps when using the low speed on the pump are the RPM's of the pump motor:
This will be shocking to many but pumps motors do not all run at 3450 RPM's- this is an average but in the real world motors run plus or minus 4-5% on either side of 3450.

Also pool pump curves are much more accurate on high speed. Operating at 1/2 the RPM's at low speed should say that the GPM are 1/2 the GPM at high speed. It it much more common than not; that the low speed GPM will be 10-20% less than 1/2 the GPM's at high speed.

This is due to impellers being designed to meet the GPM's on single speed pumps. When 2 speed were introduced no new impellers were designed for the 2 speeds and the exact same impellers are used that were used on single speed pumps.

There are many pitfalls when using 2 speeds for pools. This is just another one.

Deeker,

Thanks for the info. Very interesting stuff. What I am hearing is that pump manufacturers are purposefully providing false Lo-Speed pump curve data to the consumer.

Any other pitfalls I should be aware of besides the phony curve issue?

-Gorilla

Gorilla,
Maybe not a good excuse but two speed pool pumps are about 1% of all pump sales for a mfg. No doubt more engineering needs to be done on the low speed as well as better data provided.
Also not all mfg. are equal in the lack of correct data - one or two do have the right or close to right curves.

There is also fault that needs to be pointed at the motor mfg. Jandy, Hayward and Pentair do not make the motor. Most are supplied by AO Smith. Anybody with an experience in the industry will tell you the motor provided 10, 15, 20 years ago is far cry in quality and durability than the motors supplied today.

As far as other pitfalls with 2 speeds, beside lack of correct flows, are pools today have many more features that need to operate and these features require flow. Salt, cleaners, multiple skimmers, heaters, etc are just a few features that require more flow than most 2 speeds on low speed can handle.

Also if you have 45 GPM on low speed that will be with a clean filter. Flow reduces quickly when any restriction, such as dirt in the filter, occurs and your 45 GPM flow reduces dramatically.

I say that many people who have a 2 speed learn all the above very quickly and end up running their 2 speed pump at high speed because of some of the things I described above.

In my opinion, and others may disagree, 2 speeds are for portable spas. The pump is almost part of the spa, small body of water with very little restriction.

Deek

"In my opinion, and others may disagree, 2 speeds are for portable spas. The pump is almost part of the spa, small body of water with very little restriction. "

You can say that now,after the invention of the variable speed pool pumps, but prior to that they did serve a puropose.

I should clarify further - 2 speeds can serve a purpose on a limited number of pools, mainly older pools, but on the majority of pools today the increase in features and additional equipment that pumps need to operate has all but made them useless.
I also agree with you that variable speeds have probably driven the final stake into the heart of a 2 speed on a pool.

I decided to opt for the IntelliFlo 4x160 over the 2-speed pump... seems like a worthwhile upgrade!!

-Gorilla