Feature Request: Why don't pump controllers dynamically set RPM for heating with solar panels

[TaylorN]

In my head this is a simple problem to solve. Why can't Jandy/Pentair/etc have the variable speed pump automatically adjust RPM for solar heating. Or do they already? We already have a supply line temperature probe, I don't see why we can't have a return line temperature probe and set a min/max RPM for when there is a call for solar heat. If the input/supply water is say 8 degrees (or a user configurable threshold) or less than the output/return water, then run the pump at the min rpm (for solar). As the temperature differential ("Delta T") gets higher than 8 degrees, slowly increment the rpm say 200 RPM every Xminutes until the temperature differential is at that 8 degree threshold (plus or minus a degree or so), or until you reach the max RPM that was user set.

During spring I don't need to run the pump full blast because the solar panels aren't hot enough. And during summer, I CAN run full blast for shorter periods of time. That's just using a simple seasonal example. With proper logic in place, it would also work for time of day thermal supply, so we can collect some solar heat in the mid-morning (or cloudy day) without needing to be full speed, but the pump would ramp up later in the afternoon when their is more thermal energy available.

Seems like simple stuff to me. What am I missing?

Just trying to eek out every bit of efficiency since we live in California, and our power pricing is crazy.

 

[mknauss]

What automation system do you have?

 

[1poolman1]

In my head this is a simple problem to solve. Why can't Jandy/Pentair/etc have the variable speed pump automatically adjust RPM for solar heating. Or do they already? We already have a supply line temperature probe, I don't see why we can't have a return line temperature probe and set a min/max RPM for when there is a call for solar heat. If the input/supply water is say 8 degrees (or a user configurable threshold) or less than the output/return water, then run the pump at the min rpm (for solar). As the temperature differential ("Delta T") gets higher than 8 degrees, slowly increment the rpm say 200 RPM every Xminutes until the temperature differential is at that 8 degree threshold (plus or minus a degree or so), or until you reach the max RPM that was user set.

During spring I don't need to run the pump full blast because the solar panels aren't hot enough. And during summer, I CAN run full blast for shorter periods of time. That's just using a simple seasonal example. With proper logic in place, it would also work for time of day thermal supply, so we can collect some solar heat in the mid-morning (or cloudy day) without needing to be full speed, but the pump would ramp up later in the afternoon when their is more thermal energy available.

Seems like simple stuff to me. What am I missing?

Just trying to eek out every bit of efficiency since we live in California, and our power pricing is crazy.

How much are you willing to spend to get an option like that is the real question? When VSP came out they were "outrageously" priced at about $600 wholesale. Now the price they are online is about the same as wholesale. As these pumps keep improving in what they do, it may become an option, but the computers in the drives aren't that smart at present. Usually a solar controller or pool automation will do what you ask. The benefit is that if either the solar control or the pump drive fails you don't have to replace both.

A prime example of trying to stuff too much into a small package is the Pentair Sun Touch.

 

[TaylorN]

What automation system do you have?

Jandy Iqualink 2.0

 

[mknauss]

I am not that up on Jandy automation, but from what I see your system will do what you wish.
Read Jandy Aqualink RS - Further Reading

 

[JamesW]

Go to Speed Settings and set the speed that you want for Solar.

https://cdn.fluidrausa.com/-/media/zodiac/global/downloads/0748-91071/6594.pdf

MENU/HELP > SYSTEM SETUP > VSP SETTINGS > SELECT SPEED/LABELS > LABELS SPEEDS> CHOOSE ITEM > SELECT GENERAL LABELS/CUSTOM LABELS In the SPEED SETTINGS menu, highlight LABEL SPEEDS and press SELECT. Use the UP/DOWN arrow keys to highlight the desired PUMP, then press SELECT. Use the UP/DOWN arrow keys to highlight either GENERAL LABELS or CUSTOM LABELS and then press SELECT.

 

[JamesW]

The VSP Speed Setup table has eight entries and entries 1 through 6 are automatically associated with a function:

• When the filter/pump function runs it automatically uses Speed 1 - Pool
• If the Spa mode is enabled it uses Speed 2 - Spa
• Likewise when the Cleaner function is active it uses Speed 3 - Cleaner
• and so on with the spillover, pool heat, and spa heat functions.
• If you have a Solar system you can have Speed 7 named Solar Heat and the system automatically changes the pump speed when the Solar Heat is on.

The default VSP Speed table labels are shown in the manual and vary with the type of system you have and the dip switch settings:

 

[TaylorN]

Thanks guys.

I already manually set the RPM for solar heating, and change it per season, but it is not conducive to set it manually per day or when weather changes.

What I want is the RPM to dynamically change based on temperature differential between input water and output water. There is nothing in Jandy controller that does something like that. Jandy controller is very basic from that kind of perspective.

Which led me to just reading:

Solar Variable & Circuit Controller

EDIT [Source Code]: https://www.dropbox.com/sh/k0feg94ucntjhgi/AACU6vqU088z4NSxl2gSLIFga?dl=0 TLDR: I've been thinking about the relationship between GPM and solar heat delivered to the pool and believe it to be more nuanced than the efficiency chart we've all seen. I put together a little...

www.troublefreepool.com

...which references:

GitHub - tagyoureit/nodejs-poolController: An application to control pool equipment from various manufacturers.

An application to control pool equipment from various manufacturers. - tagyoureit/nodejs-poolController

github.com

Using that would be more along the lines of what I'd be looking for. Would only need a second temperature probe (connect to the controller(?) or somewhere) to periodically check temperature differential and adjust the RPMs accordingly.

Just wish that was in the Jandy controller out of the box.

 

[reggiehammond]

I'm not sure there's a practical effect to ramping up or down flow. The TD is fixed against the amount of thermal energy. Run faster, less TD, but more volume. Run slower, more TD, less volume. It's still the same amount of energy transferred. I can't imagine there's a lot of efficiency lost if the solar heaters are running different TDs.

 

[JamesW]

The panels should have a specified flow rate.

As long as the flow is in the range specified by the panel manufacturer, it should be good.

What is the reason you want to control the flow more precisely?

 

[Dirk]

I'm not sure there's a practical effect to ramping up or down flow.

What I want is the RPM to dynamically change based on temperature differential between input water and output water.

As James points out, your solar panels will have an optimum flow rate. As per heat exchange principles as they relate to heating a pool, the more water you pump through solar panels, the warmer your pool will get. But there is a point of diminishing return, and it's exponential. At some point, it'll cost too much in electricity to pump for very little increase in heating. And then there is the matter of how much flow and pressure your panels can handle. So panel manufacturers figure this all out for you and provide an optimum flow rate (or at least a range). My panels work most efficiently, given all the variables, at 5GPM. The manufacturer provided that number. That is per panel, times my eight panels, equals 40GPM.

Once my controller determines that there is enough heat (sun) on the panels to make the water warmer than the pool, it engages solar. That's all that needs to be calculated or adjusted. To take advantage of that heat, the flow through the panels should be at the optimum rate (40GPM in my case). There is no need, or increase in efficiency, to run the flow a little higher or lower based on how much higher or lower the available heating energy is. It doesn't work like that. It's binary, on or off, not variable.

So you only need two speeds: one for when the solar is active, and another for when it is not. The "solar on speed" is set to satisfy the optimum flow for heating, the "solar off speed" is set to accommodate whatever else is running at the time (cleaner, skimmer, SWG, whatever, or none of the above).

You don't need different solar on speeds for times of day or seasons of the year or number of clouds in the sky. Just on, or off. If you (or a controller) attempted to change the flow rate to something faster or slower, you'd just lose heating efficiency, not improve it.

 

[matthewsunshineflorida]

But there is a point of diminishing return, and it's exponential.

This is true in reverse too though, right? The manufacturer is providing that flow range for their rated BTUs which are at the highest temperature differentials. However, if the TDs are already low enough to maximize this efficiency such that it would be a diminishing return to run the pump any faster, why would we continue to run the pump at those high speeds with no efficiency gain? In other words, it isn't actually the flow itself that dials in efficiency until a diminishing return, it's TD - right? I'm not arguing we run it higher than manufacturer recommendations - I'm arguing we run it much lower when a similar TD is observed as it would be at the recommended higher speeds during peak BTU times.

What is the reason you want to control the flow more precisely?

It was out of necessity due to Irma somehow destroying my solar temp terminals and me not realizing nodejsPC could do the basics of solar without a python script. But I've been running my little project using the air terminals since late spring summer and do save a little money with no lost efficiency while also allowing for significantly faster speeds when more heat is available.

I'm not sure there's a practical effect to ramping up or down flow. The TD is fixed against the amount of thermal energy. Run faster, less TD, but more volume. Run slower, more TD, less volume. It's still the same amount of energy transferred. I can't imagine there's a lot of efficiency lost if the solar heaters are running different TDs.

While this makes sense at first glance, it doesn't prove true in practice, which is why manufacturers give recommended GPM for their panels in the first place:

• The hotter the water is heated, the closer the water temperature is to the temperature of the heat source, reducing the efficiency of the actual heating going on in the pipes. Easy way for me to think about this was if I left the water in the panels on the roof for 30 minutes, as they approach their maximum temperature, let's say 150 degrees, the rate at which temperature increases goes down as it settles closer and closer to the maximum temperature as its asymptote.
• When the water is moving through the pipes off the roof and under ground, it is losing heat to the relatively cooler environment. This effect is increased with a greater temperature differential between the heated water and the air & ground it moves through.
• Therefore, when the temperature at the return water is already so much closer to the pool/air/ground temp but still far from the solar temp, you're losing much less heat despite running it far slower to save money.

@TaylorN Now that I have a spot for another temp probe, I've considered adjusting the controller to directly adjust GPM to temperature differential rather than roof temperature - but that would probably be wasted time since it's already pretty well tuned in for my setup. You're welcome to make that happen with the code there - it's not pretty particularly since there's no direct speed assignment, but it's been rock solid with nodejsPC and pm2 since May.

 

[TaylorN]

The panels should have a specified flow rate.

As long as the flow is in the range specified by the panel manufacturer, it should be good.

What is the reason you want to control the flow more precisely?

I want to control the flow more precisely because of the power consumption from the pump in the mid-morning, cloudy, or spring/late-fall. San Diego, CA charges extreme amounts per kilowatt hour, and I don't believe it is optimal to run at the manufacturer's recommended GPM during those scenarios.

My solar will automatically turn on sometime midmorning because the air temp exceeds the threshold versus the pool water (from the solar setup by the guys who installed it), but the temperature differential is tiny. So for 2-3 hours before midday the pump is running at the manufacturer's recommended GPM, but is wasting electricity. Yes I can set the schedule so solar can't be called mid-morning and would only have a chance to turn on during the middle of the day to late afternoon, but there is some usable heat in the mid-morning that could be delivered at that time if I could just get the solar valve to open and run at the low speed my SWCG usually runs at. It would essentially collect some "free'ish" heat and delivering it to the pool.

Running at 2800RPM is about 1,000watts, which is perfect for our panels during summer time 11am to 3pm. The temperature differential is optimal. It runs off and on and is able to keep the pool really warm with very little ON time.

If its mid-morning, cloudy, or spring/late-fall, running at 2800RPM is not needed. If I can run at 1900 RPM during those times I can save like 700watts per hour and still deliver some heat to the pool. If left it at 2800rpm it would most of the day, but that heat wouldn't be worth the extra 700watts per hour. The temperature differential when running 2800rpm during mid-morning, cloudy, or spring/late-fall, is very low. Its like warming up a fire house with a match (not the best analogy). I'll have to dig up what I read in the past, but there is an ideal temperature differential, and that could easily be achieved by dynamically changing the RPM after reading the input and output temperatures. My example of 1900 vs 2800 RPM is obviously just two static numbers, but we could be operating somewhere in between all day every day. We have hardware that could easily control this stuff.

 

[JamesW]

but the temperature differential is tiny.

You can change this.

 

[TaylorN]

The panels should have a specified flow rate.

As long as the flow is in the range specified by the panel manufacturer, it should be good.

What is the reason you want to control the flow more precisely?

In my mind, that optimal flow rate provided is for summer time during the mid to later half of the day. There is no real benefit to going above that number, but there is a lot of room to play with at lower flows depending on time, season, and weather. It seems pool related equipment is lazy. Instead of being more complex they opt for the simple approach of it can't hurt to run the same GPM, regardless of if it wastes electricity. Look how long it took Variable speed pumps to come into play and for people to figure out how to use them optimally. Right? I dunno

 

[TaylorN]

You can change this.

Thanks James.

But I want the solar to turn on early in the day, I just don't want the RPM to be running as high. And it would be nice if the RPM was determined by temperature differential so I don't have to manually adjust based on time of year... let alone time of year and time of day (which is not feasible)

 

[TaylorN]

This is true in reverse too though, right? The manufacturer is providing that flow range for their rated BTUs which are at the highest temperature differentials. However, if the TDs are already low enough to maximize this efficiency such that it would be a diminishing return to run the pump any faster, why would we continue to run the pump at those high speeds with no efficiency gain? In other words, it isn't actually the flow itself that dials in efficiency until a diminishing return, it's TD - right? I'm not arguing we run it higher than manufacturer recommendations - I'm arguing we run it much lower when a similar TD is observed as it would be at the recommended higher speeds during peak BTU times.


It was out of necessity due to Irma somehow destroying my solar temp terminals and me not realizing nodejsPC could do the basics of solar without a python script. But I've been running my little project using the air terminals since late spring summer and do save a little money with no lost efficiency while also allowing for significantly faster speeds when more heat is available.


While this makes sense at first glance, it doesn't prove true in practice, which is why manufacturers give recommended GPM for their panels in the first place:

• The hotter the water is heated, the closer the water temperature is to the temperature of the heat source, reducing the efficiency of the actual heating going on in the pipes. Easy way for me to think about this was if I left the water in the panels on the roof for 30 minutes, as they approach their maximum temperature, let's say 150 degrees, the rate at which temperature increases goes down as it settles closer and closer to the maximum temperature as its asymptote.
• When the water is moving through the pipes off the roof and under ground, it is losing heat to the relatively cooler environment. This effect is increased with a greater temperature differential between the heated water and the air & ground it moves through.
• Therefore, when the temperature at the return water is already so much closer to the pool/air/ground temp but still far from the solar temp, you're losing much less heat despite running it far slower to save money.

@TaylorN Now that I have a spot for another temp probe, I've considered adjusting the controller to directly adjust GPM to temperature differential rather than roof temperature - but that would probably be wasted time since it's already pretty well tuned in for my setup. You're welcome to make that happen with the code there - it's not pretty particularly since there's no direct speed assignment, but it's been rock solid with nodejsPC and pm2 since May.

Dude!

You snuck this in while I was replying to the other messages. Excellent write-up!

I totally agree, using the air temp on the roof would probably be just as effective as setting RPM based on temp differential. Just two ways of solving the problem. I might argue temp differential would be slightly more accurate, but just being able to programmatically control RPM would be a huge increase in efficiency.

San Diego electricity prices can be anywhere from $0.25 to $0.50 per kwh during the middle of the day when solar heat is available and needed.

Time of Use, TOU, Pricing Plans, TOU Pricing Plans | San Diego Gas & Electric

www.sdge.com

just be thankful to not have to pay $0.83 per kwh during on-peak time!!!!

 

[TaylorN]

@TaylorN Now that I have a spot for another temp probe, I've considered adjusting the controller to directly adjust GPM to temperature differential rather than roof temperature - but that would probably be wasted time since it's already pretty well tuned in for my setup. You're welcome to make that happen with the code there - it's not pretty particularly since there's no direct speed assignment, but it's been rock solid with nodejsPC and pm2 since May.

Can you explain what you mean by a spot for another temp probe? Are you talking available in your piping, or on the controller? Where do you plug the second temp probe in on your controller? or are you using the temp probes separate from the controller? I haven't had a chance to dive into your complete setup yet. Probably going to be a few days.

 

[matthewsunshineflorida]

Can you explain what you mean by a spot for another temp probe? Are you talking available in your piping, or on the controller? Where do you plug the second temp probe in on your controller? or are you using the temp probes separate from the controller? I haven't had a chance to dive into your complete setup yet. Probably going to be a few days.

I just meant that I put another 1/2" NPT tee when I did my heater bypass and acid pump. Intellicenter has 3 sets of 10k ohm terminals for air/solar/water. I'm using air/water since solar is shot, but you can easily add more sensors to njsPC directly. My setup is actually very basic given what njsPC can do - I use it primarily as a "remote" on a fixed tablet by the pool with Tasker and Alexa to control the pool, music, TVs, pool alarm. I'm still only using intellicenter for the back end automation, except the solar controller and a circuit enforcer script. @rstrouse is the one you REALLY want to see. He has probes that, in conjunction with njsPC, entirely automate everything from his ph to his FC. He's also one of the primary developers! You could even run njsPC in lieu of ANY automation using just relays and probes - it's incredible how much it can do.

But for me right now, my hybrid setup with a stock intellicenter and njsPC is smooth enough that I haven't bothered to do more.

 

[KevMo]

just be thankful to not have to pay $0.83 per kwh during on-peak time!!!!

That is crazy. Many people in Texas wouldn't be able to use their air conditioners at even your lowest rates. My lowest monhly usage is usually around 1,500 kwh in February. The Texas heat and my 10.5 tons of AC pushes the usage to around 5,000 kwh in July & August.

We don't have any time of use billing. On my last bill the all-in rate was $0.1233 per kwh. I have an Emporia Energy monitor on each of my pool circuits. The total cost to run all pool related-power in August was $46.69. I am not trying to rub it in - I do eny your weather! I understand why it makes sense to carefully control the level and time of usage of your pool equipment. If you don't have an energy monitor already, I reccomemd getting one on your whole house or at least your pool. The Emporia version works well and is very easy to install and use.