Hot tub mod to make use of overnight cheap rate

bintyandthebeast

FreeBear said:

bintyandthebeast said:

FreeBear said:

bintyandthebeast said:

- there is no timer on the internal heater, it’s set-and-forget. If I wanted to raise temp I would need to go out at midnight every day to do this and shortly before 5am to reduce temp again manually (taking my sorry self outside in the cold and wet in the middle of the night!)

A programmable (smart ?) thermostat with a remote temperature sensor would do the job. But.... They are not designed for use outside, so would need a suitably sealed box. Nor are they capable of switching large loads, so you'd need to use a contactor (heavy duty industrial relay) to switch the heating element on/off.

Point me in the right direction and I'll take one!

One at random - https://www.ebay.co.uk/itm/293794288892 - Comes with a remote sensor that you can dangle in the water (check that it is waterproof first). It claims to have a 16A relay fitted, but I would never trust a cheap Chinese relay to switch heavy loads repeatedly. You also need to check the range of temperatures that can be programmed in.

Or if you are feeling masochistic, whip up a control system using an Aduino, ESP32, or Raspberry Pi.

Great for a controller but still needs the immersion part which seems to be the issue unfortunately

ThisIsWeird

bintyandthebeast said:

ComicGeek said:

FFHillbilly said:

does the solar diverter not have a timer function? that would be the simplest way of doing it. the Myenergi Eddi has a boost function, just set the boost times for the cheap rate period

just read it again and I see the solar diverter is currently installed on the hot water only. also I did have an idea of adding a contactor to control the power supply to the hot tub, but this coming on off in the middle of the night is unlikely to work as the hot tub may require buttons to be pressed to get it to turn on?

what about just adding a heat pump to it? https://www.thetubcompany.co.uk/heat-pumps/

The heat pump was what I was thinking. Strangely we have just had a swimspa and heat pump installed by The Tub Company this summer. 

There's no timer function on the swimspa (like the OP's hot tub) - you set the required temperature and then the heater kicks in as and when to achieve this. But the heat pump I have installed (to replace the electric heater) has an integral timer within the app control, so I can either set it to run at cheap night time rates, or in the afternoon when I'm likely to have excess solar generation or spare capacity in the batteries. 

I'm also getting an efficiency of 800% from the heat pump on a warm day like today, so major running cost savings. 

That would be ideal but ROI would be maybe 7/8 years based on what I can see. If I found one for say £1,000 that would be great but they're considerably more than that. Maybe one day when we can stretch to a swimming pool we'll get one 🤔

Keep an eye out on t'Bay and Fb for second-user - I bet they'd be a small fraction of the new price.

Possibly.

bintyandthebeast

I guess what I need is someone with electronics experience who could build & install something that would have a timer between 12 and 5am to override the thermostat so the tub runs up to 40 degrees. No idea if that's a realistic possibility

ComicGeek

bintyandthebeast said:

ComicGeek said:

FFHillbilly said:

does the solar diverter not have a timer function? that would be the simplest way of doing it. the Myenergi Eddi has a boost function, just set the boost times for the cheap rate period

just read it again and I see the solar diverter is currently installed on the hot water only. also I did have an idea of adding a contactor to control the power supply to the hot tub, but this coming on off in the middle of the night is unlikely to work as the hot tub may require buttons to be pressed to get it to turn on?

what about just adding a heat pump to it? https://www.thetubcompany.co.uk/heat-pumps/

The heat pump was what I was thinking. Strangely we have just had a swimspa and heat pump installed by The Tub Company this summer. 

There's no timer function on the swimspa (like the OP's hot tub) - you set the required temperature and then the heater kicks in as and when to achieve this. But the heat pump I have installed (to replace the electric heater) has an integral timer within the app control, so I can either set it to run at cheap night time rates, or in the afternoon when I'm likely to have excess solar generation or spare capacity in the batteries. 

I'm also getting an efficiency of 800% from the heat pump on a warm day like today, so major running cost savings. 

That would be ideal but ROI would be maybe 7/8 years based on what I can see. If I found one for say £1,000 that would be great but they're considerably more than that. Maybe one day when we can stretch to a swimming pool we'll get one 🤔

I got mine for £1079, supply and install. That was for a larger 12 kW model, so might be worth looking at - the pool heat pumps aren't as expensive as house heat pumps. 

Even today when it was 8 degrees outside it was running at 600% efficiency, delivering 12kW of heat for only 2 kW of electricity. 

FFHillbilly

bintyandthebeast said:

ComicGeek said:

FFHillbilly said:

does the solar diverter not have a timer function? that would be the simplest way of doing it. the Myenergi Eddi has a boost function, just set the boost times for the cheap rate period

just read it again and I see the solar diverter is currently installed on the hot water only. also I did have an idea of adding a contactor to control the power supply to the hot tub, but this coming on off in the middle of the night is unlikely to work as the hot tub may require buttons to be pressed to get it to turn on?

what about just adding a heat pump to it? https://www.thetubcompany.co.uk/heat-pumps/

The heat pump was what I was thinking. Strangely we have just had a swimspa and heat pump installed by The Tub Company this summer. 

There's no timer function on the swimspa (like the OP's hot tub) - you set the required temperature and then the heater kicks in as and when to achieve this. But the heat pump I have installed (to replace the electric heater) has an integral timer within the app control, so I can either set it to run at cheap night time rates, or in the afternoon when I'm likely to have excess solar generation or spare capacity in the batteries. 

I'm also getting an efficiency of 800% from the heat pump on a warm day like today, so major running cost savings. 

That would be ideal but ROI would be maybe 7/8 years based on what I can see. If I found one for say £1,000 that would be great but they're considerably more than that. Maybe one day when we can stretch to a swimming pool we'll get one 🤔

The ROI is never going to be 7/8 years. You can probably get them installed for under £1000. I work at several holiday cottages and they all have them, they say that the cost is 25% of mains electric heating. they only run the hot tubs in summer months so they are always going to be efficient so it makes sense. it seems like the ideal application for a HP to me, only used in warmer months so ambient temp is 10-20 degrees, and only required to heat to 40 degrees means they can get a CoP of 4 easily, or 4 times better than regular electric heating

bintyandthebeast

I’ve found these guys who tell me my warranty can be left intact with their range: https://energiwizz.com/products/
looking at the spec I am not sure it will do what I want (make use of the overnight cheap rate for electric) but does indicate it will save me money. 

As we have solar panels and an “efficient” hot tub the running cost issue I’m trying to reduce is for winter months. We’ve woken to frost this morning and can get to -12 to -16 degrees here. Even with the covered pergola helping with maintaining temp for the tub and keeping the efficiency of the heat pump as high as possible I don’t see a COP of 4 being realistic. I do in summer, but that’s not when I will need to make a saving. 

If I were able to get a time installed to turn on the circulation pump and heater overnight then (in my mind) that’s the winner. I reckon I’d save what I am hoping to & warranty remains intact.

ComicGeek

bintyandthebeast said:

I’ve found these guys who tell me my warranty can be left intact with their range: https://energiwizz.com/products/
looking at the spec I am not sure it will do what I want (make use of the overnight cheap rate for electric) but does indicate it will save me money. 

As we have solar panels and an “efficient” hot tub the running cost issue I’m trying to reduce is for winter months. We’ve woken to frost this morning and can get to -12 to -16 degrees here. Even with the covered pergola helping with maintaining temp for the tub and keeping the efficiency of the heat pump as high as possible I don’t see a COP of 4 being realistic. I do in summer, but that’s not when I will need to make a saving. 

If I were able to get a time installed to turn on the circulation pump and heater overnight then (in my mind) that’s the winner. I reckon I’d save what I am hoping to & warranty remains intact.

I'm not convinced you have the summer months sorted. Unless I've missed something, you don't have a home battery. So currently the hot tub heater kicks in whenever it needs to to keep the tub at the set temperature - at times that will coincide with excess PV generation, but you can't control that and the likelihood is that your heater is operating mainly in the early morning after cool nights and when the PV isn't yet producing. You really need to monitor the hot tub circuit and see how much it's drawing and when. The circulating pumps will also have a significant 24/7 base load - my swimspa has a base load of around 300W, and can draw 9kW when all jets are on!

At least with the heat pump option you can set the timer on the heat pump - I can set mine to run during off peak, or manually turn it on when I've got excess PV to dump in the pool.

That weblink is for just one of the many pool heat pump suppliers, but they look expensive. I got a 12
kW Inverpac heat pump installed for half the price of the supply only price for their 5.5 kW. Your ROI is dependant on finding the right product for the right price. You would be best to find an installer first, and then talk options with them in terms of budget.

DanielBeynon

I know this is an old thread but in case someone comes across it.

I bought a heavy duty wifi control that I put between the supply and the tub.  It's worked great for a few years so far.  I've set it so the tub comes on 1am-6am aligned with my 5p cheap rate:

https://toughleads.co.uk/collections/hot-tub-leads-and-accessories/products/heavy-duty-wi-fi-control-switch-230-415v-16a-32a-options

I then run it an hour in mid morning and an hour early evening aligned with my 14p "mid" rate window and we've never had issues with the water.  Hope that helps