Putting a Smart Switch on my Hot Tub heater

[Dirk]

I think he needs to qualify his statement a bit more that SSR can handle higher loads (amperage) then mechanical contact relays.

However this does not come without some other complexities. You need to read the fine print...

Solid state relays are SPST,... Three-phase loads can be controlled using 2 or 3 SSR’s. Use 3 SSR’s for Y or star 3-phase loads using a neutral line. Two SSR’s will control “delta” loads with no neutral line. Three solid state relays are also used when there is no neutral load to provide redundancy and extra assurance of control.

To dissipate the heat, an SSR must be mounted on a finned heat sink or aluminum plate. An SSR should be located where the ambient temperature is relatively low, since the current switching rating is lowered as the temperature increases.

Another SSR characteristic is a small leakage current across the output when the relay is open. Because of this, a voltage will always exist on the load side of the device.

It is essential that a properly rated, fast blowing I2T fuse be installed to protect the load circuit.

I found similar caveats. And they are considerably more expensive, too.

 

[phonedave]

… old school analog switches with the big chunky levers …

www.concordaerospace.com

However, for the record, I do have a lot of smart stuff in my house - but then I work in that industry (kind of) so there is that.

 

[JamesW]

You don’t switch AC with relays…you need to switch at zero cross-over, use something like this SSRL with SCR technology.

For a standard resistance heater, there is probably no reason to use anything other than a regular relay.

Some equipment might require equipment protection, but the resistance heater in hot tubs is controlled by a regular On/Off relay.

 

[wayner]

I just wonder is it that much of a savings to require such efforts?
If the tub is at temperature & closed, maintaining that temp is not that hard & requires little energy. You can further assist this (prevent heat loss) by adding a solar cover under the regular cover.
Its been hashed out here time and again that it’s much cheaper to maintain the temp of your tub than to turn it down then back up again which is what this is essentially doing.
The only time it is more cost effective is if you will be not using the tub for an extended period. So we suggest turning it down while on vacation.
If energy consumption is an issue reducing the circulation pump frequency will help. Most people find the factory default schedule is a bit overkill.

I have been monitoring the switch and it seems that the heater kicks on about twice per day for about 30 minutes at a time. So it isn't like there is going to be a huge fall in the water temp when the switch is off and not allowing the heater to kick on. So by controlling when the water is heated I will save, best case scenario, $1 per day on weekdays and $0.25 on weekends. The heater will likely kick on more as temperatures fall.

I don't know that it makes sense to have the circ pump run less frequently. Isn't that a protection for freezing during very cold temperatures as the water lines are not insulated? I am also putting temperature probes in the water and in the tub enclosure and it seems that the tub enclosure stays pretty warm. So it will be interesting to see if the enclosure goes down below 0C on the coldest days here in Toronto which are usually around -15C or so.

 

[wayner]

I believe the poster's intent was to shift power usage to a (much cheaper) time of day, not to save energy overall.
"Overnight my costs are 2.4c/kWh. From 4-9pm the cost is 24c/kWh – 10X higher."

This is exactly the point. I want the heater on from 11pm-7am, maybe on a bit during the rest of the day, but I never want it to come on from 5-9pm when my power is very expensive.

 

[wayner]

Nice project. Results will be interesting, so I'm mostly just following along.

I would say that is too close (agreeing with Matt). That 80% rule is what I would have also quoted. A bigger margin would have been even better, to cover the hammering he's describing. I would have chosen a lesser device (cost and ratings) and then had it operate a high-wattage relay. That would have taken all the heat stress off the device, and placed it on a dumb relay, properly rated to take it. You'd lose the monitoring, but I suspect you're going to eventually lose that device anyway. Mounting it in a water tight (air tight) box will hasten its demise.

Yes, the other thing I was considering was using a dry contact relay to flip an actuator. That is the old school way of doing it, one downside of that is that I don't get the power monitoring. The nicest thing about the power monitoring is that I know when the heater is actually on and heating the pool. I would lose that unless I came up with another way of sensing an active power load.

 

[Mdragger88]

I have been monitoring the switch and it seems that the heater kicks on about twice per day for about 30 minutes at a time. So it isn't like there is going to be a huge fall in the water temp when the switch is off and not allowing the heater to kick on. So by controlling when the water is heated I will save, best case scenario, $1 per day on weekdays and $0.25 on weekends. The heater will likely kick on more as temperatures fall.

I don't know that it makes sense to have the circ pump run less frequently. Isn't that a protection for freezing during very cold temperatures as the water lines are not insulated? I am also putting temperature probes in the water and in the tub enclosure and it seems that the tub enclosure stays pretty warm. So it will be interesting to see if the enclosure goes down below 0C on the coldest days here in Toronto which are usually around -15C or so.

Saving $1 a day is certainly a worthwhile venture.
I am lucky that we don’t get as cold as you so I don’t worry about circulation frequency as much unless there’s an extended power outage. Even when we had one at the beginning of this year my tub kept its temp pretty well for the several days we were out.

 

[wayner]

I am trying to use some DS18B20 temperature probes to monitor the temperatures of (1) the water, (2) the inside of the tub enclosure, and (3) the ambient air temperature. I wanted to use these with another Sonoff device which is a THR320D - which is a switch which also has an RJ9 input for the temperature probes. But I am having issues getting the third party temperature probes to work and I might have to use a Raspberry Pi instead for that.

Once I have the temperature probes I may then just write my own code to use as a "thermostat" and keep the tub temperature setting at the max. This way I can have more control over heating both in terms of when to use the heater and whether I also want to let the temp go down a bit on weekdays as I almost never use the tub during weekdays, usually just on weekends.

And having a probe inside the enclosure lets me monitor the temperature inside the enclosure to assess the risk of freezing. If the enclosure is always well above freezing, even on the most frigid days, then I need to worry less about having the heater kick on to keep the temperature up. But it seems like a 1200 litre tub of water, even well insulated, and a heater kicking on a couple of times a day keeps the temperature warm-ish inside the enclosure. And this is despite some gaps at the bottom of the enclosure which are, presumably, air vents.

As someone said earlier, none of this is necessary, but for an enthusiast it is interesting and fun to know more about the functioning of your tub.

 

[Newdude]

Saving $1 a day is certainly a worthwhile venture

Ok. Here me out. I know a way for you to save $3+ a day. It's this thing that's kinda like your pump, except it can run much slower for mondo savings. Wait !!! Maybe it'll make more sense in Mistyspeak.

= = =

= = =

 

[Mdragger88]

Ok. Here me out. I know a way for you to save $3+ a day. It's this thing that's kinda like your pump, except it can run much slower for mondo savings. Wait !!! Maybe it'll make more sense in Mistyspeak.

= = =

= = =

Except I don’t think his venture has quite the initial investment like a vsp.
I’ll get a scooter soon enough lol

 

[wayner]

Ok. Here me out. I know a way for you to save $3+ a day. It's this thing that's kinda like your pump, except it can run much slower for mondo savings. Wait !!! Maybe it'll make more sense in Mistyspeak.

= = =

= = =

How is it mondo savings in a spa? How much do the pumps run in a spa?

In a pool that runs 12-24 hours per day I can see that, but in a spa it doesn't run that much, unless you are in the spa for hours per day. And when you are in the spa don't you want the pumps running at full power to give as much pressure to the jets as is possible?

But even in my pool my pump uses about 1kW. I run it around 16 hours per day, and during low price times when the all in cost would average about $0.10/kWh. How much would I save with a variable speed?

 

[Newdude]

How is it mondo savings in a spa? How much do the pumps run in a spa?

It was a long standing side convo about getting rid of her single speed pool pump. Sorry for the distraction.

 

[Dirk]

I am trying to use some DS18B20 temperature probes to monitor the temperatures of (1) the water, (2) the inside of the tub enclosure, and (3) the ambient air temperature. I wanted to use these with another Sonoff device which is a THR320D - which is a switch which also has an RJ9 input for the temperature probes. But I am having issues getting the third party temperature probes to work and I might have to use a Raspberry Pi instead for that.

Once I have the temperature probes I may then just write my own code to use as a "thermostat" and keep the tub temperature setting at the max. This way I can have more control over heating both in terms of when to use the heater and whether I also want to let the temp go down a bit on weekdays as I almost never use the tub during weekdays, usually just on weekends.

And having a probe inside the enclosure lets me monitor the temperature inside the enclosure to assess the risk of freezing. If the enclosure is always well above freezing, even on the most frigid days, then I need to worry less about having the heater kick on to keep the temperature up. But it seems like a 1200 litre tub of water, even well insulated, and a heater kicking on a couple of times a day keeps the temperature warm-ish inside the enclosure. And this is despite some gaps at the bottom of the enclosure which are, presumably, air vents.

Check this out, there may be something you can use:

The Ultimate Thermometer

How ultimate? Hey, it’s me! Since I became a pool owner I’ve been trying to find a good solution for reading both my pool temperature and my outdoor temperature. I’ve been through the obvious ones: floating in the pool, or stuck to a window. But I also had a need for my home automation system...

www.troublefreepool.com

As someone said earlier, none of this is necessary, but for an enthusiast it is interesting and fun to know more about the functioning of your...

@Newdude, see? If you don't want to be my friend, I'll just go make another!

 

[Dirk]

Yes, the other thing I was considering was using a dry contact relay to flip an actuator. That is the old school way of doing it, one downside of that is that I don't get the power monitoring. The nicest thing about the power monitoring is that I know when the heater is actually on and heating the pool. I would lose that unless I came up with another way of sensing an active power load.

I was thinking your Sonoff would run the relay. You'd lose actual watts used (if it can do that), but you'd still have access to the on-off times. I suppose when you wrote "actually on" you meant not monitoring just when the timer was supposed to turn the pump on/off, but actually monitoring the current flow. But there might be another way to keep an eye on that (some sort of device that wraps around the wire and monitors the current). There's probably a Raspberry Pi solution for that. The device I'm using in the thread I just referred you to could probably do that, too.

 

[wayner]

This Sonoff switch is a "wet contact", no point in using this larger, more expensive device to flip a relay. By actually on I did mean when the heater was actually heating water. There probably is some other device to use, I haven't seen one, but I am sure there is something out there. Or you could put a temp sensor on the heater.

 

[wayner]

Check this out, there may be something you can use:

Looks very cool, I am playing around with HA these days. I have a Home Automation system called Control4, which is very good, but it is a closed system and you technically need a dealer to do a lot of things to the system unless you are ok with Jailbreaking your system, which I have done. But then you need drivers to integrate it with other types of hardware. It seems like almost any type of smart/IOT device now has interfaces with HA and I may also use some sort of interface between HA and Control4.

 

[phonedave]

but I never want it to come on from 5-9pm when my power is very expensive.

Between 5 and 9 PM is when I am using my hot tub 90% of the time.

 

[wayner]

Between 5 and 9 PM is when I am using my hot tub 90% of the time.

That doesn't really matter with respect to when the heater is active. The switch that I installed just cuts power from the power block to the heater, but the pumps still get power and work. And in my tub when the main pumps are going the heater shuts off, I guess that there is not enough power to the tub to power the two main pumps plus a 5.5kW heater.

So as long as the tub is at the desired temperature at 5, or close, then this isn't an issue. Currently the temperature decay of the tub is such that the heater only kicks on about every 12 hours, it may kick on more now that the weather is below freezing. And once you are done with the tub you don't really care how warm it is until the next time you use it, so the temp may fall while you are using it between 5 and 9, and it won't heat up until 11pm, but that doesn't matter.

 

[Mdragger88]

That doesn't really matter with respect to when the heater is active. The switch that I installed just cuts power from the power block to the heater, but the pumps still get power and work. And in my tub when the main pumps are going the heater shuts off, I guess that there is not enough power to the tub to power the two main pumps plus a 5.5kW heater.

So as long as the tub is at the desired temperature at 5, or close, then this isn't an issue. Currently the temperature decay of the tub is such that the heater only kicks on about every 12 hours, it may kick on more now that the weather is below freezing. And once you are done with the tub you don't really care how warm it is until the next time you use it, so the temp may fall while you are using it between 5 and 9, and it won't heat up until 11pm, but that doesn't matter.

I was under the impression that’s why you’d want a 220v tub - so you could run jets & heat at the same time especially in colder climates. I guess they don’t all operate this way?

 

[wayner]

I was under the impression that’s why you’d want a 220v tub - so you could run jets & heat at the same time especially in colder climates. I guess they don’t all operate this way?

My spa is a Jacuzzi J-345 from about 2006, but I know that others have said that their spas also don't heat while the jets are going. My heater is 5.5kW. So that is about 23A at 240V. Adding a couple more kWs for the pumps would be getting up there.