Thread: Information & diagram on how to install External Thermostat to Heat Pump

Yep, connecting external equipment to heat pump control panels is easy, which pump do you have? I can post diagrams for Dream and Duratech. If it's not one of those, I can try to obtain the information for you.

On the main circuit board there is a link (marked EXT in the diagram below) that can be replaced by external control equipment. You can connect your external stat in this place.

You can also connect additional equipment, such as a timer, in series with this link and it is the correct place to control the heat pump by external equipment. The electronics only require a low current contact rather than the high current contact you would need if you attempt to control the power supply to the heat pump or to the compressor itself. There is also some electronics behind this link that protects the compressor against rapid cycling or any other circumstance that may damage it.

Just two steps:

1. Take the live and neutral supply for the stat from the mains input connector block. (You should include a small fuse holder with a 3 amp or 3.15 amp fuse for safety).
2. Connect the stat contact in place of the link marked EXT.

BTW this link can control the pump from any other device you might think of such as a timer - just make sure that you use a volt free contact for all external devices and connect them all in series.

You've got the best bloke giving you info on heaters
Manky Sanke knows his onions

Originally Posted by mwy62831

Manky Sanky


Thanks for the information, I will give it a go . I am thinking of using a TLZ 11 Microprocessor or similar used by many of the Koi suppliers (Pro Digi-Stat Controller. Is that what you would recommend ?

I've never used that stat, or any other proprietary stats, when I've controlled heat pumps by external equipment because I used to design and and fit custom made control panels for all types of leisure equipment including swimming pool filtration equipment and heat pumps.

So I can't vouch for it personally but it has a good specification and is designed around well tried and tested digital technology and microprocessors that are widely used. This range is also recommended for koi keepers and I've not heard any bad reports. The only negative point I have about this range is that, they are designed to be installed in control panels where fingers don't have access so the connector terminals aren't enclosed to avoid accidental contact, especially with the mans terminals. I normally advise potential users that they can fit the stats in a suitable plastic box or glue a suitable finger shield over any exposed connection.

Originally Posted by Manky Sanke

Yep, connecting external equipment to heat pump control panels is easy, which pump do you have? I can post diagrams for Dream and Duratech. If it's not one of those, I can try to obtain the information for you.

This is excellent news. Do you have a diagram for Duratech that you can share for me?

Many thanks.


Sent from my iPhone using Tapatalk

There y'go Ash,

As with the Dream heat pump below there are just two steps:

1. Take the live and neutral supply for the stat from the mains input connector block. (You should include a small fuse holder with a 3 amp or 3.15 amp fuse for safety).
2. Connect the stat contact in place of the link marked DI01 and GND

As with the Dream heat pump, this link can control the pump from any other device you might think of such as a timer - just make sure that you use a volt free contact for all external devices and connect them all in series.

That's correct Scratch,

The external stat should be set to the required temperature and the internal stat should be set to a higher temperature. I recommend setting the internal stat to a degree or so higher than the external stat so that the internal stat will prevent the pond temperature rising above this point if the external stat should fail in the "calling for heat" mode.

edit: I went in too fast, found another topic "what do you do in winter" that goes into more details on temps.. oops , plus I also found my answer in an excellent article Aeromonas alley

Really happy to came across this thread and already ordered an external controller. Thanks! Maybe a bit off-topic and probably already discussed but can't find it straight away. What temps do you advice to keep, that is, for an uncovered pond. I'd like to follow the seasons/winter. I don't want to go below 4-5 degrees, but what is considered the "danger zone". I've read 8-12degrees, other say 6-10.. just curious on your findings

cheers
philippe

So I spoke to a technician of where I bought the heatpump. He said most "swimmingpool" heatpumps have thermostats not lower then 15degrees, because otherwise the gas inside could go liquid when everything is too cold, and it may damage/break the heatpump. He said you can go down to 10degrees with external stat but shouldn't go much lower. Any of you here have any experience/advice on this? I'd say all those heatpumps are more or less similar, if not from the same chinese manufacturer. Mine doesn't go lower then 15 degrees, but would like to go a bit lower during winter

I couldn't agree with that. I ran a swimming pool company for over 30 years and I never heard of such a limitation. I've worked on more installations than I can remember where heat pumps were the source of heat for swimming pools and/or environmental control systems which heated and dehumidified pool buildings which were intended to be in use all year even in the harshest winter.

The reason heat pumps for swimming pools don't control water or room temperatures below about 15°C is simply that no one would want to swim at that temperature or be in a pool hall that was only heated to 15°C. So there was no need to design a stat that had a control range that went below that value - pure economics, nothing else.

As for the supposed risk that the refrigerant might turn from a gas to a liquid, anyone who understands how a heat pump works would know that it's important for the refrigerant to condense to a liquid after the expansion valve before it re-evaporates to a cool gas in the evaporator before being re-compressed to a hot gas by the compressor. See the diagram below for a basic explanation and my more detailed explanation on my website on this link:
Good water guide: pt 8

Trust me, in thirty plus years of seeing air source heat pumps operating in freezing conditions, I've never seen that happen or heard of anyone else having that problem.

Heat pump efficiency reduces as air temperatures fall but a common refrigerant, R22, evaporates from its liquid phase to its gaseous phase at -40.8°C (ok, I knew it was very low but I confess that I just looked it up). Therefore, as long as the air temperature is a few degrees above that, it will always be in its gaseous state when it reached the compressor. Even if the air temperature was below that so that the refrigerant was still liquid when it reached the compressor, as soon as it began to compress, the heat would instantly turn it back to a gas again.

Heat pumps become very inefficient at low temperatures but they don't blow up, catch fire or go into catastrophic meltdown!!

Not a clue without a bit more information but I could possibly tell you if you posted a picture of where it connects to inside.