I am about to lose my head...

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taekwondodo

taekwondodo

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Apr 26, 2009
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OK, not yet, but I'm about to....

This is a customer's pool - not my design, just something I've been working (dealing) with the customer for almost a year... The previous owner "home built" the pool (~17,000gal), and should have found TFP first.

All of the plumbing is 1.5", skimmers on one line, MD on another, T'ed to 2" at the pad to the pump. Return is 1.5". Pump is 2HP WhisperFlo, valve off to Polaris PB4. I know... worthless without pictures...

Filter (DE) pressure averages around 32psi clean, to 38 dirty - system is currently clean. And to really make things difficult, the whole pad is about 8' below the pool - so you have to shut-off ball valves to work at anything at the pad - or get deluged with water.

I know the pump's wayyyyyy over-sized for the pipe, and have discussed with the customer he'd be much better off changing out the pump... He doesn't have the funds right now.

Note: Using the 2.31xPSI indicates the TDH is around 90 (suction+pressure), which says the WFE shouldn't have any flow moving through the system(via the head curve). I can indeed say that there's plenty of water coming out both returns... including the sweep when the PB4 is running.

The issue that continually comes up is that right after my customer moved in, he purchased and had a Heat Pump installed (not by, or from me). It worked for a while - he was keeping it on year-around... But within a few months of being installed, it started giving an "HP3" alarm.

HP is the alarm given on the "AC" compressor: "Compressor High Pressure", and the system shuts down after three tries of starting up (hence, "HP3" flashing on the unit) and needs power-cycled to re-start.

The vendor (Rolm Industries) was swearing it was the flow switch. It's a standard binary flow-switch: Flow = closed, 0 ohms. No flow = open, infinite ohms. They sent a flow switch and asked me to install it (and paid me for it). I opened up the unit, and ohmed-out the existing flow switch. Pump on = 0 ohms. Pump off = infinite. Left the pump on. A few minutes of trying to start up, the thing goes HP, HP, HP3 and turns off. Still zero ohms on the flow switch. I took the new flow switch, taped it "closed" and wired it in (prior to cutting any pipe) and still got the HP3.

Fortunately, the system had a circuit diagram on it and I located the "HP" switch - it's on the AC-side of everything. AC ain't my bailey-wick (what does that mean, anyway...), but I'm smart enough to be able to ohm-out the HP switch and verify that it's open (infinite ohms, should be closed = zero ohms) when the system was trying to start up and the pump was on.

Stick with me... this is in "Pumping Station" (and not "Everything Else") for a reason.

So, the vendor calls up an AC guy, and the AC guy comes out and this guy "fixes" the unit by swapping out the pressure-switch on the AC side of things. The unit works great for a few months... then starts going "HP3" again.

My customer calls the vendor, vendor says we're not getting enough flow through the system... deja-vous? I tell the customer that there's no way that there's not enough flow (minimum flow for the switch to engage is 20GPM).

Then, the vendor says that because the pad is ~8' below the pool, that the extra pressure/head because of the distance the pump needs to push the water up is causing the HP (remember, the HP isn't in the flow of the water at all, it is part of the freon's circulation path). "Hello? Water drops 8' before it rises 8' - system is sealed both to and from the pool..."

Now, the vendor says they finally got it. There's too much flow through the water side of the unit - their system is rated for max 70GPM, and now they want me to put in a flow-bypass on the system.

The customer sent me the installation manual tonight, and it does indeed recommend a bypass when water is flowing >70GPM... I am just very skeptical that when I re-plumb (and charge the vendor) that this is going to work... While getting paid is nice, I want to do right by "my" customer.

So, given the details, does the last statement make any sense? IDTS, but wanted to bounce it off of others first. And, if I install the bypass, without a flow-meter on the heat-pump side, exactly how will I know how much water's going through the bypass vs. through the heat-pump? Schlock, I say...

Thanks.

- Jeff
 
You definitely need to get the filter pressure down. You don't need to change the pump, you can just switch to a smaller impeller (I'd go with a 3/4 HP impeller).

Most heaters and heat pumps do not have a "flow" switch, they have a pressure switch, which is a big difference. There can be pressure without any flow. I had a similar issue with a heat pump where the flow was blocked by internal debris in the unit. The pressure switch closed, but there was no flow and it caused the unit to malfunction. At 8 feet down, you have to adjust the pressure switch or replace it with an actual flow switch. At 8 feet below water level, the pressure switch can close even when the pump is off and the heat pump can run without any flow.

I recommend the following:

1) Replace the impeller with a 3/4 HP impeller.
2) Put a flow switch in the control loop of the heat pump.
3) Install a flow meter to the heat pump.

You should not need a bypass with the smaller impeller. The flow meter will confirm the flow rate going to the heat pump.

http://www.pentairpool.com/pdfs/WhisperFloOM.pdf

http://www.blue-white.com/products/Vari ... ctpage.asp
 
Thanks, I want to get a flow meter in the loop before I cut into or change anything, but want the Vendor to pay for it as part of the warranty - so we can take the question of flow out of the discussion. I like the idea about the impeller too - I'll look into it and talk to the customer... after we determine where we are with flow.

- Jeff
 
Something doesn't sound right about the psi. That's just about the max a pool pump can produce and would suggest something VERY restrictive on the pressure side. That or a bad guage.
 
I vote for putting a flow meter in the discharge. I agree with Dave about the pressure too. You need to verify the gauge.

Of course I don't think any of this is your problem. Maybe a rash of bad pressure switches, maybe the A/C guy overcharged the system a little and the warm weather is creating a high pressure situation, maybe it's a bad board? I don't know but I doubt it's high water flow through the system.
 
Nothing to do with the flow rate being too high is going to cause a "Compressor High Pressure" error. If the flow rate was too low you could get that error, but I agree that flow rate too low is not plausible in this situation. There are a couple of other problems on the AC side that could cause that error.
 
I agree about the high pressure - I don't like it, but can't get the customer to swap out the pump... the whole pad is a real challenge. I don't know what the self-builder/owner-before-him was thinking with 1.5" return piping.

Oh - and the gauge is good... It's just 2HP followed by a lot of backpressure caused by the pipe. It will go to zero when off, and rises as expected from 30-ish to 35ish over time.
 
Note: Using the 2.31xPSI indicates the TDH is around 90 (suction+pressure), which says the WFE shouldn't have any flow moving through the system(via the head curve). I can indeed say that there's plenty of water coming out both returns... including the sweep when the PB4 is running.
Click to expand...

With the pad below water level, filter pressure will run higher than normal (+3.5 PSI) and suction lower than normal (-7" hg). Without a suction measurement, the only thing you know for sure, assuming the gauge is correct, is that the return head is about 77' including elevation change. The suction will be very low due to the elevation change so the total head loss may be close to 77'. But I have some additional questions:

Which 2 HP does the customer have. Uprated or full rated?

How long are the runs from pool to pad?

How many return eyeballs does the pool have and what is the diameter of each?

Has the filter pressure always been that high?

Can you put the filter into bypass mode and if so, what is the pressure then?

Are there any check valves in the plumbing?

Even if I assume the worst case plumbing, I can only get the filter pressure up to about 28 PSI so I suspect something else is going on.
 
If the water flow rate is too high/fast, the ability of the heat pump to transfer heat to the water is/could be diminshed. This would result in the inabiity of the refrigerent to condense properly. If that happened, the hot refrigerent would stay at high pressure for a longer period casuing the high pressure switch to trip.
Just guessing here, but it's all i can come up with at the moment.

I wouldn't mess with the pump at this point. Just plumb in a bypass to cut the flow rate a bit and see if that fixes the problem.
 

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mas985 said:
Note: Using the 2.31xPSI indicates the TDH is around 90 (suction+pressure), which says the WFE shouldn't have any flow moving through the system(via the head curve). I can indeed say that there's plenty of water coming out both returns... including the sweep when the PB4 is running.
Click to expand...

With the pad below water level, filter pressure will run higher than normal (+3.5 PSI) and suction lower than normal (-7" hg). Without a suction measurement, the only thing you know for sure, assuming the gauge is correct, is that the return head is about 77' including elevation change. The suction will be very low due to the elevation change so the total head loss may be close to 77'. But I have some additional questions:

Which 2 HP does the customer have. Uprated or full rated?

It's an old pump - I would have to look...

How long are the runs from pool to pad?

The pad's about 15' (tops) away from the pool...

How many return eyeballs does the pool have and what is the diameter of each?

Two...

Has the filter pressure always been that high?

Yes... first measurement/reading was over a year ago at 30PSI. It's varied upwards as it gets dirty... to about 38.

Can you put the filter into bypass mode and if so, what is the pressure then?

Can't do that - standard Waterway 60 with P/P valve...

Are there any check valves in the plumbing?

No - Just ball valves. But if I had my way (i.e., if he would pay me for it) I would rip out all plumbing and re-plumb...

Even if I assume the worst case plumbing, I can only get the filter pressure up to about 28 PSI so I suspect something else is going on.
Click to expand...
 
I can get to about 30 PSI adding a little more head loss to the pad and using 2 - 3/4" eyeballs. With that, my best guess is there is about 72 GPM @ 72' of head. There is about 1' of head gain on the suction side due to the 8' water drop.

Given the flow rate is right at the edge of the recommendation, it could explain why it works for a while. Have you or the owner noticed that the problem happens after the filter is cleaned? One way to test this is to add some head loss on the return side with one of the valves or perhaps restriction one of the eyeballs.

Also, a very simple fix would be to just change out the impeller. The owner would recoup the costs in fairly short period of time.
 
The heat pump (Calorex) that I had problems with had a 1-inch pipe for a heat exchanger, and at one point, the line had a diameter of about 1/2 inch, which ended up blocked by debris that had gotten into the line. This damaged the heater and it needed to be replaced.

If possible, you should check the heat exchanger tubing for blockages. I think that downsizing the impeller is a good idea. Adding a flow meter and a flow switch would also be good ideas.
 
So - from the vendor...

"With the set up of Mr. Jones’ heat pump he is going to have intermittent HP issues. As per your conversation with Joe today we always recommend 2” plumbing to help with the water flow through the unit, the smaller the plumbing , 1 ½”, the more pressure and the faster the water flows through the heater, not giving a chance for the heat transfer to take place which can cause the unit to go off on HP. The pictures Mr. Jones sent us also show the plumbing going up and down a wall which can also cause HP issues, he also has a 2 hp pump which is moving the water at an excessive rate. We recommend a check valve on the inlet and outlet side to help with the HP issues. Please let us know if you have any further questions. Thank you."

lol...
 
taekwondodo said:
not giving a chance for the heat transfer to take place which can cause the unit to go off on HP. ..
Click to expand...

I believe I've heard that before but the idea was dismissed:wink:
Not sure a check valve will do much, nor the 2 inch pipe. But a bypass to decrease the flow might work. What you got to lose by putting one in?

FWIW, I think the guys right. If the high side cant dissipate the heat, the pressure will get too high and trip the HP switch.
 
It is pretty easy to slow down the flow rate (i.e. add head loss) and see if that helps the situation. If it works, then there are several options to consider.

But the thing I don't understand is why he said this:

, the smaller the plumbing , 1 ½”, the more pressure and the faster the water flows through the heater
Click to expand...

Smaller plumbing reduces flow rate not increases it. The velocity of the water is higher in the PVC pipe but not the heater.
 

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