Fan coil unit installation

[JohnMo]

Fan coil being installed in garden room to replace UFH, which really didn't work well unless at flow temperatures. Which wasn't an option with the ASHP and the main house heating demand.

 

So Christmas eBay search led to me buying a Myson iVector MkII fan coil 1.2m wide. This unit can do heating and cooling and has a variable fan cut in temperature, so should allow me run weather compensation.

 

Unfortunately the unit needs to placed on the opposite side of the summer house to the existing water entry point. So instead of running pipes internal, have decided to run them externally. 

 

Some photos of progress

 

Unit wall mounted

 

Cover installed

 

The unit I got is a 4 pipe fan coil. This unit has a dedicated cooling and seperate heating heat exchangers.  The heat transfer area of the combined heating and cooling HE's is about 50% larger than a 2 pipe fan coil. Have piped the two HE's as a single unit. I am using a Salus self balancing actuator to balance the flow rate through the fan coil.

 

Have started the external piping using 15mm Hep2O and 25mm wall thickness insulation. The insulation to aluminium tape covered to keep mice away and UV to stop sun damage. The pipes sit on metal brackets 40mm off the ground and are galvanised banded into place.

 

 

[JohnMo]

Progress today, piping all completed and system cleared of air. Unit running.

 

Have reverted to WC for house and set back to an older heating curve that worked fine.  That should lower ASHP flow temp be 5 degs, from current settings.

 

Just need to check the garden room gets up to temperature.

 

To do

Seal opening through wall

Insulation to be added to all joints

Final run around all the bottle vents to ensure all air out of system.

Paint the aluminium taped insulation to match woodwork.

[JohnMo]

So got the unit running last night and over a few hours it heated the room. Heat pump ran continuously during the period. However once heated the heat pump started to cycle an hour on hour off.  The summer house temp drops to 17 from 20 overnight. It did the same again today, took most the morning to recover, then over the next few houses drops to 17.

 

So scratching head on how to setup.

 

Can do two running regimes

Thermostat, this starts and set fan speeds, but if water drops below 32 (adjustable set point) fan stops.

Or you can run at a set fan speed, but no thermostat.

 

Anyone with some experience of what works best?

[JohnMo]

Tried the unit overnight with fan set in manual mode at a constant min speed overnight. Heat pump ran over the full period except a few defrosts (-2 overnight). This morning the summer house had settled to 20.1 degs. Will monitor it over today. 

 

Have built a WC curve based on the running parameters and added to heat pump. Curve starts at 10 deg outside temp with 29 degs flow temp. At -6 outside flow temp is 39.6 deg. Suspect a little modification will be required, so will monitor.

 

Next issue is humidity has dropped like stone, it's currently at 35%, so will reduce dMEV fan to min speed.

[HughF]

How are you finding the self balancing actuator working for you? I've got £2.99 isolation valves on my fan coils and I struggle to throttle them down to get any meaningful deltaT across them without them being noisy...

[JohnMo]

9 minutes ago, HughF said:

How are you finding the self balancing actuator working for you? I've got £2.99 isolation valves on my fan coils and I struggle to throttle them down to get any meaningful deltaT across them without them being noisy...

 

I have set my fan to manual min speed, the heat pump isn't being asked to do much, as the mixer is set to 28 deg flow to UFH.  Currently heat pump is kicking out about 36 degs. It's been cycling on off today. The room temp is very stable, water temp is varying from 36 down to about 27.

 

This is the plot from my H&T sensor to can see where the heat pump flow temp dips with the peaks and troughs. I may have to tweek the WC curve a little.

 

 

The Salus actuator is on the return piping side and "hand on" pipes, there is a difference in temperature so it's doing something. Used on a radiator straight trv from Screwfix, item 48346 - Straight TRV about £15, which gives a positive shut off for maintenance also. Have powered it on all the time to the main incoming power.

 

No noise from the valve

[JohnMo]

Tried the fan coil on auto mode again today, and just cooled the room down.

 

Reverted to manual fan operation and room temp settled to where I wanted it (after a few hours).

 

The reason could be the Salus auto balancing actuator, auto mode switches the fan to different speeds and to off, so maybe dT is just changing too quickly for the actuator to keep up as it will have been tuned for UFH, not a coil containing a litre of water.

 

So manual mode with WC is probably the way to go. It keeps it simple.

 

 

[HughF]

I run mine wide open on the isolators now that we’re up at the top end of the WC curve at 47.5 flow.

 

Mine are just the smiths ecovectors with a simple thermal switch and two speeds. The bathroom one stays on 24/7 and the downstairs ones go on/off as required by hand. My wife is of a certain age so she often turns them off in a moment of meltdown.

[JohnMo]

On 15/01/2024 at 17:10, HughF said:

How are you finding the self balancing actuator working for you? I've got £2.99 isolation valves on my fan coils and I struggle to throttle them down to get any meaningful deltaT across them without them being noisy...

Have just removed the Salus actuator, as I was getting random drops in room temperature for no apparent reason. Checked system for air and nothing found.

 

Last night the heat pump ran continuously, fan speed on fan coil is at speed one, steady temperature outside. Over a period of a few hours this morning, room temp dropped a few degrees. Removed actuator and installed a manual decorating valve and now room temp is recovering.

 

Will monitor over the next few days.

[HughF]

I must say, I've been quite pleased with the fan coil option for heating the kitchen and hallway - they definitely seem to work well.

[JohnMo]

To allow me to run the summer house temperature at the most economical temperatures and be at the right temperature at the right time, I have added a thermostat. The thermostat sets two different flow temperatures on the heat pump rather than switching off the water flow. The first is ok for a set back temperature, but also more suitable for house heating, the second temperature is 2 degs hotter (may need to adjust) and is more suited to the garden room.

 

Now have a simulator for a DHW probe installed and this has freed up a set of contacts to allow the double set point on the heat pump to be used. So when make contacts (via the thermostat NC contacts) the lower set point is set, when break contacts (thermostat demand on) another temp set point is set.

[JohnMo]

Some success after reading @Bramco reply on another thread.

 

Sort of using what he does to batch charge, but have a longer run time to keep the fan coil happy so have batch charge curve based on outside temperature, the batch charge lasts for nearer 10 to 12 hrs depending on outside temp.

 

On 01/02/2024 at 10:03, Bramco said:

 

@JamesPa  Flow out is about 30C and back is around 25C.  The ASHP is set to 35C but even when it's not defrosting, it never reaches this, so it runs continuously for the full 4 hours.  When it has to defrost, you can see a dip in both the ASHP output and input and the UFH feed and return.

 

I think we'd set the ASHP setpoint to 35C to aim to get a flow temp approaching that but with the way things work, i.e. the ASHP never really reaching the setpoint, it's actually probably working optimally, in that when the ASHP doesn't have to defrost it runs continuously, so is probably getting a great COP.  Sadly can't see this on the Cool Energy units - I'm considering putting one of the open energy monitor ASHP kits in so that we can see what we're really achieving but that means draining down the ASHP loop to put a heat meter in, so will have to be done in the summer.

 

Graphs below to give you an idea of how things work - our build was almost passive house, very airtight, MVHR, insulated slab with embedded UFH loops, so we don't need much heat and when the slab is warm we don't lose heat v fast.

 

Warm night, so a bit above normal, no defrost.

 

 

Cold night with defrost. Given it was very cold, the immersion in the UFH tank we use for a boost when it's below 5C was probably also on.

 

 

So now have the heat pump set up to run and chase a slightly elevated temperature, with floor acting as huge buffer, so getting long run times, which in turn keeps the fan coil happy and charges the floor in a single run, heat pump is not having to modulate much.

 

Leave it run a few days then assess if I should dump WC all together. The flow temp today got to 31 and the house thermostat tripped the UFH off at 20.5.

Edited February 3 by JohnMo

[JohnMo]

Bit of fine tuning over the last few days (still a little more to do, to optimise flow temps) have added a double set point to the heat pump. This is selectable by volt free contacts. Both high and low temperature run the same WC curve but start at different flow temperatures.

 

Normal curve

Start temp is 28 at 12 deg outside temp increasing to 32 degs at -9

 

High temp curve

Start temp is 31 at 12 deg outside temp increasing to 35 degs at -9

 

So basic operation is the garden room has a thermostat, which is timed to call for heat about an hour or so before I need it hot. This opens the double set point contacts via the thermostat and brings the heat pump on to its higher operating curve, all other times it's on the lower operating curve. The house thermostat is set to 0.5 degs hotter than at the same time, and house floor then acts as a buffer. The heat pump runs continuously during this period except for defrosts.

 

The fan coil is left in auto mode, with a target temp of 22. It was -5 overnight and has got up to 1 deg today, no issues with the fan coil room temp didn't drop below 20 degs was up to 22 this morning.