Frost Stat

[Biggles]

My CH control is good when I have the inverter on as I have a remote room stat, which requires the inverter to be on.

 

I arrived at the boat today and it was 8c and not that cold outside and now I am concerned that the boat could freeze up although I do have all wet systems anifreezed.

 

So what I want to have is a frost stat that is TOTALLY not dependent on any external power. Basically a BiMetal switch set to say 5c that I can hack into my GSM remote switching curcuit.

 

I guess what I need is some sort of old type room stat.

 

Any suggestions?

[by'eck]

Can't remember the make hooked up to my Mikuni as not on boat, but its AA battery driven.

 

It offers adjustable target and fall back temperatures and a fixed 5°C frost setting, either of which can be chosen. Two on/off cycles per day as well.

 

Google for battery driven timer stat.

Edited November 27, 2012 by by'eck

[Ally]

Beware, some frost stats are detrimental to such as a webasto or eberspacher as they cause them to flick on and off too frequently without performing the full function. What system do you have? It may be preferable to fit a seven day timer that runs say 4-8 times a day.

[by'eck]

Just found the Siemens one fitted to my boat on the Mikuni site. Click for info.

 

 

The RJD10 doesn't cause excessive cycling and in any case is Mikuni recommended. Typically it cuts in about 2° below the target temperature and cuts out on or 0.5° above.

 

In the timed AUTO mode it works to one of two daily on/off cycles to maintain the target temperature. This typically means its off for at least 45 minutes before it cuts in again within a single timed period, although it has the familiar advance button for manual override.

 

The frost setting if selected maintains the fixed 5°C continuously. I would guess it cuts in around 3°C to achieve this.

 

The adjustable fall back temperature is the one it maintains in AUTO during an off period. Like the frost setting its also selectable for continuous operation. It could therefore be used as a higher frost setting, say 8°C.

Edited November 28, 2012 by by'eck

[Old Son]

I have a Horstmann DRT-2. It has around 6No. on's and off's plus the thermostat functionality. The good part is that it runs on either 1 or 2 1.5 volt batteries that last around 12 months. I use it with an eberspacher hydronic 10. I tend to set the tempratures a little high and adjust the heat in the boat with the TRV's on the radiators.

[mrsmelly]

My CH control is good when I have the inverter on as I have a remote room stat, which requires the inverter to be on.

 

I arrived at the boat today and it was 8c and not that cold outside and now I am concerned that the boat could freeze up although I do have all wet systems anifreezed.

 

So what I want to have is a frost stat that is TOTALLY not dependent on any external power. Basically a BiMetal switch set to say 5c that I can hack into my GSM remote switching curcuit.

 

I guess what I need is some sort of old type room stat.

 

Any suggestions?

 

Are you on mains hook up? Personaly if I were a hobby boater on mains I would do what my bro in law does and leave two oil fired rads on, works a treat for him. Of course if you are not then a 12v timer would be my choice.

 

Tim

[Biggles]

Just found the Siemens one fitted to my boat on the Mikuni site. Click for info.

 

 

The RJD10 doesn't cause excessive cycling and in any case is Mikuni recommended. Typically it cuts in about 2° below the target temperature and cuts out on or 0.5° above.

 

In the timed AUTO mode it works to one of two daily on/off cycles to maintain the target temperature. This typically means its off for at least 45 minutes before it cuts in again within a single timed period, although it has the familiar advance button for manual override.

 

The frost setting if selected maintains the fixed 5°C continuously. I would guess it cuts in around 3°C to achieve this.

 

The adjustable fall back temperature is the one it maintains in AUTO during an off period. Like the frost setting its also selectable for continuous operation. It could therefore be used as a higher frost setting, say 8°C.

 

 

I have a spare one of these supplied by Mikuni so OEM. I installed the RF version which requires the inverter to be on hence the need for a simple frost stal.

 

Thanks for suggesting this I had wondered if having 2 controllers on one circuit wold be a problem but I suspect it won't it will only call on one or the other and if other kicks in one will override the other. The main thing is the standard one will work as a frost stat.

 

I am off grid but not live aboard but am here 3-4-5 days a week.

[by'eck]

I have a spare one of these supplied by Mikuni so OEM. I installed the RF version which requires the inverter to be on hence the need for a simple frost stal.

 

Thanks for suggesting this I had wondered if having 2 controllers on one circuit wold be a problem but I suspect it won't it will only call on one or the other and if other kicks in one will override the other. The main thing is the standard one will work as a frost stat.

 

I am off grid but not live aboard but am here 3-4-5 days a week.

 

You haven't mentioned what heating system you are controlling but the Mikuni/Webasto/Eberspacher are commanded on or off by a simple switch which is what most of these controllers provide.

 

However having two will not necessarily work if they are in the same command circuit. e.g. if wired in series then if either stat commands off the heater won't come on. If in parallel then if one stat commands on the other will be ignored.

 

The Siemens one I suggested will cover all requirements except 7 separate day timing.

[Biggles]

Mikuni. MX60 and they would be wired in parallel. I will give it a look in the next few days.

[Biggles]

Reporting back.

 

Got the the boat today. I deliberately didn't turn the CH on prior to setting off for the boat. The reason for this was to see if the frost stat (parallel controller) would kick in.

 

The only way of checking this was to see if the water in the tank was warm.

 

I am pleased to report the frost stat works. The water in the tank was well above tepid meaning the boiler had fired. Both the stats were reading 5°c so the boat was well above frost levels.

 

Outside it was -1.5°c

 

Job Done :-)

[by'eck]

Good to hear your frost stat setting worked.

 

I'm in a similar situation with an unattended boat in a marina, on shore power with batteries floating.

 

Mikuni MX40 left powered feeding three radiators & calorifier coil.

 

Same Siemens thermostat/timer in frost stat mode fixed at 5°C and not subject to timer.

 

When working in normal room temp mode it seems to trigger on about 2° below target temperature, so I'm guessing around 3°C.

 

Question is will the Mikuni be cycling on for too short a period than is good for it in present conditions, north west England.

[smileypete]

Good to hear your frost stat setting worked.

 

I'm in a similar situation with an unattended boat in a marina, on shore power with batteries floating.

 

Mikuni MX40 left powered feeding three radiators & calorifier coil.

 

Same Siemens thermostat/timer in frost stat mode fixed at 5°C and not subject to timer.

 

When working in normal room temp mode it seems to trigger on about 2° below target temperature, so I'm guessing around 3°C.

 

Question is will the Mikuni be cycling on for too short a period than is good for it in present conditions, north west England.

It'll help if the stat is some way away from the rads and pipes.

 

There are cheap 12V temp controllers that let you set the differential, so it could come on at say 1C and off at 7C:

 

http://www.ebay.co.uk/itm/221147036126

http://www.willhi.com/Documents/WH7016Cdatasheet.pdf

 

Another way to do it is with a latch relay and delay relay, bit fiddly though.

 

cheers, Pete.

~smpt~

[Biggles]

I think the cycling won't really be an issue. It will take a fair time to raise 2c. Plenty long enough for a proper burn cycle.

[by'eck]

I think the cycling won't really be an issue. It will take a fair time to raise 2c. Plenty long enough for a proper burn cycle.

 

That's re-assuring thanks. Stat is on opposite bedroom wall to radiator which will help.