OK some fan coil unit questions

[MikeSharp01]

3 hours ago, Originaltwist said:

these DIY jobs?

Interesting. I have one 'radiator' unit I brought to put in the MVHR supply line to allow heating / cooling but I could get another and make two of these, one for each bedroom! 

[joth]

15 hours ago, MikeSharp01 said:

Secondly do I need to provision for a condensate drain back to the plant room and away or can an evaporative approach be taken as in most fridges?

 

I run the condensate drains into the nearest bathroom waste stack. Put it through a dry-running trap and down the drain it goes. Not sure why you'd want it in the plant room specifically.

However, as said above if you run the ASHP just above dew point and can still avoid short cycling (e.g. by running UFH+FCU together no zoning) then you can probably skip the condensation drain altogether. 

[haythorn_1]

How do you run it with no zoning? Do you take it off the same manifold as the UFH? Or just have a separate manifold with no actuators?

[JohnMo]

58 minutes ago, haythorn_1 said:

How do you run it with no zoning? Do you take it off the same manifold as the UFH? Or just have a separate manifold with no actuators?

You take it off the UFH manifold, I have tee'ed into the flow and return before the UFH manifold. I have a 2 port valve that isolated that circuit only when there is a call for DHW. All other times the 2 port valve is open.

 

Thing to also remember a decent fan coil will just look after itself. They generally have an in-built controller, modulating fan speed based on target temperature. They generally need an external temp sensor for cooling, but work well without doing heating. I just set mine to manual for cooling. No real need to stop flow going to the fan coil, as they work differently to radiators.

[Originaltwist]

On 19/08/2024 at 10:51, JohnMo said:

Mine runs via two thermistors, one temp above for heating and the temperature below for cooling. A simple pipe stat x2 could do that. Normally open for one normally closed for the other.

thanks @JohnMo that would work - expensive though. This liitle chap starts at 40c and stops at 25c , a bit limited but under £10 from RS

i have to say I have searched in vain for something similar for the cold side

 

[JohnMo]

I was thinking more simple, but also adjustable 

 

https://www.toolstation.com/corgi-pcs-dual-pipe-cylinder-thermostat/p68281

 

[G and J]

3 hours ago, JohnMo said:

I was thinking more simple, but also adjustable 

 

https://www.toolstation.com/corgi-pcs-dual-pipe-cylinder-thermostat/p68281

 

Has that got 3 connections (common, no, & nc I mean)?

[JohnMo]

1 hour ago, G and J said:

Has that got 3 connections (common, no, & nc I mean)?

You would need two one for heat one for cooling. One uses common plus normally open, this would then close when you hit say 25 the fan would start. When cooling set to say 15 but wire to the normally closed, any flow temp above 15 would not switch on fan. You most likely run via a relay to stop power back feeding itself. You would only use this on @Originaltwist fan coil.

[haythorn_1]

On 19/08/2024 at 17:59, JohnMo said:

You take it off the UFH manifold, I have tee'ed into the flow and return before the UFH manifold. I have a 2 port valve that isolated that circuit only when there is a call for DHW. All other times the 2 port valve is open.

 

Thing to also remember a decent fan coil will just look after itself. They generally have an in-built controller, modulating fan speed based on target temperature. They generally need an external temp sensor for cooling, but work well without doing heating. I just set mine to manual for cooling. No real need to stop flow going to the fan coil, as they work differently to radiators.

 

Where do you have the pump in this setup?

[G and J]

2 minutes ago, haythorn_1 said:

 

Where do you have the pump in this setup?

I think I know the answer to this but as I’m not sure I’ll wait for others who do know to answer.    

[JohnMo]

46 minutes ago, haythorn_1 said:

 

Where do you have the pump in this setup?

In the heat pump, just a single circulation pump. Everything run as a single zone or DHW heating.

Edited August 25 by JohnMo

[haythorn_1]

Makes sense. I guess the only draw back is you cannot circulate water through the UFH without the heat pump being on. I have read some do this to distribute water that has been heated by sun in exposed rooms.

[JohnMo]

28 minutes ago, haythorn_1 said:

cannot circulate water through the UFH without the heat pump being on

You can and mine does it all the time.

 

I run pretty much pure weather compensation so the heat pump is energised and ready to go and circulation pump on all the time, except 

 

1. During cooling the house drops below 20.4.

2. During heating the house goes over 23.1

A thermostat stops the cooling or heat demand.

 

During cooling and heating I have the temperature settings set, so they automatically modulate the heat pump output to match demand. So in cooling when the house is sitting at about 21 the heat pump compressor will run for about 10 mins every the hour or two. When the sun's out and we get plenty of temperatures rise, the heat pump compressor can run 40 mins an hour every hour. All done by the heat pump sensing the return temp - the restart hysterisis of 4.9 for the compressor and flow temp target set to 14.5, so when the floor goes above 19.4 the ASHP compressor starts. Heating is done in a similar way. The continuous circulation helps even room temp and gives the fan coil a flow of cool water for continuous slow cooling effect.

[haythorn_1]

Wow, good to know. Thanks!

[JohnMo]

1 minute ago, haythorn_1 said:

Wow, good to know. Thanks!

It's taken me a year to get there!

[G and J]

6 hours ago, G and J said:

I think I know the answer to this but as I’m not sure I’ll wait for others who do know to answer.    

 

5 hours ago, JohnMo said:

In the heat pump, just a single circulation pump. Everything run as a single zone or DHW heating.

WOO HOO!   I got it right.   I think I’m starting to get there!  If it wasn’t so late I’d crack open a cream soda to celebrate!

[G and J]

3 hours ago, JohnMo said:

You can and mine does it all the time.

 

I run pretty much pure weather compensation so the heat pump is energised and ready to go and circulation pump on all the time, except 

 

1. During cooling the house drops below 20.4.

2. During heating the house goes over 23.1

A thermostat stops the cooling or heat demand.

 

During cooling and heating I have the temperature settings set, so they automatically modulate the heat pump output to match demand. So in cooling when the house is sitting at about 21 the heat pump compressor will run for about 10 mins every the hour or two. When the sun's out and we get plenty of temperatures rise, the heat pump compressor can run 40 mins an hour every hour. All done by the heat pump sensing the return temp - the restart hysterisis of 4.9 for the compressor and flow temp target set to 14.5, so when the floor goes above 19.4 the ASHP compressor starts. Heating is done in a similar way. The continuous circulation helps even room temp and gives the fan coil a flow of cool water for continuous slow cooling effect.

To check my understanding, your summer/winter switch determines if you are in mode “1. During cooling…” or mode “2. During heating…”.

 

I’m guessing automating that switch would require logic beyond thermostats.  Do you have a schematic/written description of the settings in case someone else needs to fix a fault with the system?  (If you do guess who wants a copy!)

 

 

[JohnMo]

5 minutes ago, G and J said:

your summer/winter switch determines if you are in mode “1. During cooling…” or mode “2. During heating…”.

Correct

 

8 minutes ago, G and J said:

guessing automating that switch would require logic beyond thermostats.

My automation is simple - the wife says for for a day or two "it's cold/hot isn't it". Flick summer winter switch, set thermostat to heat or cool. Takes about a minute twice a year - not worth the effort to automate. Trouble with automation you could get into heat cool ping pong without realising 

[G and J]

1 minute ago, JohnMo said:

My automation is simple - the wife says for for a day or two "it's cold/hot isn't it". Flick summer winter switch, set thermostat to heat or cool

That made me laugh.  I’d still love to understand your system at a very detailed level, mind, but it still made me laugh. 

[JohnMo]

Will go on to the computer tomorrow and add a copy - has all the settings etc

[G and J]

31 minutes ago, JohnMo said:

Will go on to the computer tomorrow and add a copy - has all the settings etc

You star.  🙂

[JohnMo]

9 hours ago, G and J said:

You star.  🙂

As promised - system layout and control. My DHW is a bit more convoluted than normal as the cylinder is remote from everything else and needed an additional pump, so hydraulically separated via a CCT

Heating Layout and Control.pdf

[G and J]

7 hours ago, JohnMo said:

As promised - system layout and control. My DHW is a bit more convoluted than normal as the cylinder is remote from everything else and needed an additional pump, so hydraulically separated via a CCT

Heating Layout and Control.pdf 45.58 kB · 11 downloads

Thank you.  
 

Rather than fire tons of questions at you I’m going to try and work out as much of that as I can first.   Then I’m going to fire tons of questions at you, but at least I’ll have tried lol

[LnP]

12 hours ago, JohnMo said:

As promised - system layout and control. My DHW is a bit more convoluted than normal as the cylinder is remote from everything else and needed an additional pump, so hydraulically separated via a CCT

Heating Layout and Control.pdf 45.58 kB · 13 downloads

Very interesting. Thanks @JohnMo for sharing. I'm not clear though what happens to the ASHP when you're in summer mode and the DHW calls for heat. I can understand how a call for heat from the DHW makes the 3 port valves turn and the CCT pump start. But won't that send chilled water to the cylinder? What tells the ASHP to switch to winter mode and start producing heated water?

[JohnMo]

1 minute ago, LnP said:

Very interesting. Thanks @JohnMo for sharing. I'm not clear though what happens to the ASHP when you're in summer mode and the DHW calls for heat. I can understand how a call for heat from the DHW makes the 3 port valves turn and the CCT pump start. But won't that send chilled water to the cylinder? What tells the ASHP to switch to winter mode and start producing heated water?

When on cooling mode there is always a slug of cold water that gets sent to cylinder coil. Not much different to the ASHP being off, the whole pipe contents will have cooled down to atmospheric temp. So a call for DHW heating then a similar slug would also get sent to the cylinder. Nothing clever seems to occur.