Do fan coil radiators need a condensate waste?

[SBMS]

Pretty much as title says..  considering fancoil rads for our upstairs again instead of a ducted AC system… would like to use them for cooling as well. Does each fan coil need a condensate drain for cooling?

[JohnMo]

Ideal answer is yes, then you can flow any temperature you want, without concern.  If you are also flowing through UFH loops, you can get away without. All really depends on flow temp. Risk free answer is you need drains

[SBMS]

11 minutes ago, JohnMo said:

Ideal answer is yes, then you can flow any temperature you want, without concern.  If you are also flowing through UFH loops, you can get away without. All really depends on flow temp. Risk free answer is you need drains

Does all flow and return pipe work need lagging as well if running cold water through?

[joth]

Yup agree with all that. A few additional motivators for including condensate drains would be 

- if you want to use cheap overnight rate or free solar PV to "boost" the cooling then you need to be able to run at cold temps, ideally sub 10° to get most from the HP

- if you have one big FCU ducted into multiple rooms it will likely have to work harder than lots of smaller FCUs, each installed inside the single room it services. 

- if you have lots of solar gains, poor insulation or even poor airtightness then o/c the FCUs will need to work harder (aka colder) than a super insulated low solar gain building 

 

Tldr YMMV but having the drains gives flexibility 

[joth]

20 minutes ago, SBMS said:

Does all flow and return pipe work need lagging as well if running cold water through?

Yes. Not just pipework but all pumps, valves, filter, etc.

And pipes lagged before clipping.

All standard practice in commercial but good luck finding a residential installer competent at doing this

Edited December 2 by joth

[SBMS]

3 minutes ago, joth said:

Yup agree with all that. A few additional motivators for including condensate drains would be 

- if you want to use cheap overnight rate or free solar PV to "boost" the cooling then you need to be able to run at cold temps, ideally sub 10° to get most from the HP

- if you have one big FCU ducted into multiple rooms it will likely have to work harder than lots of smaller FCUs, each installed inside the single room it services. 

- if you have lots of solar gains, poor insulation or even poor airtightness then o/c the FCUs will need to work harder (aka colder) than a super insulated low solar gain building 

 

Tldr YMMV but having the drains gives flexibility 

Thanks @joth  do you have fan coils yourself?

[joth]

12 minutes ago, SBMS said:

Thanks @joth  do you have fan coils yourself?

Yes think I was one of the first on here to do this, mostly documented in this thread

Although the second one I got for the office (eBay job ripped out of a restaurant) seems to have died so I'm now eyeing up getting a third. 

 

 

[JohnMo]

Converse to the above, my pipes are not insulated in the room and I have no condensation drain. But I flow at UFH (cooling) flow temps, over a long period - so above dew point. Certainly not as effective as really cool flow temps, but acceptable 

[G and J]

We’ll be running drain pipes to our Fancoil locations in case.  The cost of a bit of pipe for first fix is tiny. The hassle of doing it later is huge.  
 

However, to get lots of supercool from our fancoils I’ll need to zone them and that won’t be day one, we’re going to try using them above the dew point.  (Crumbs, I almost sound like I know what I’m talking about!)

[SBMS]

7 hours ago, G and J said:

We’ll be running drain pipes to our Fancoil locations in case.  The cost of a bit of pipe for first fix is tiny. The hassle of doing it later is huge.  
 

However, to get lots of supercool from our fancoils I’ll need to zone them and that won’t be day one, we’re going to try using them above the dew point.  (Crumbs, I almost sound like I know what I’m talking about!)

Have you picked a fan coil unit?

 

also - what happens if the units are cooling and then the DHW program starts? 

[G and J]

1 hour ago, SBMS said:

Have you picked a fan coil unit?

Not finally, as we won’t be buying them till next summer at the earliest and availability changes and new stuff is launched.  I’ve been working on the premise in various design areas that by finding one solution that is economically and technically viable, and allowing for the requirements that that option requires, we have a base case which we may be able to improve upon when the time comes to order.  
 

I’ve been looking at Reverso units, which seem a sensible design and cost.

[G and J]

1 hour ago, SBMS said:

what happens if the units are cooling and then the DHW program starts? 

It’s a bit like alcohol and sound logic.  Both exist but not at the same time.

 

In our case we might use spare solar power directly to heat the water when the sun shines and we need cooling.  But we might not, we might just use schedules to have a blast of hot water (should be reasonably efficient on a warm day therefore not take too long and still have a decent COP), and then run on gentle cooling the rest of the day.

 

At the mo I think I’ll be wiring to allow the installation of a solar diverter but start without one.  Less (kit) is more (money left in the piggy bank).  Or maybe less (kit) is less (balance on the mortgage).

[-rick-]

I would assume that if the water circuit diverts to DHW then the flow through the fan coil would stop. However, unless you spent extra on controls the fan would keep going until the temperature in the non-flowing water normalised and at that point no further cooling would take place until the flow started again. I think most fan-coils sense the water temp so if it goes outside of range the fan stops, but it wouldn't be a big deal if it carried on - it would just circulate air, not provide cooling.

[joth]

1 hour ago, SBMS said:

also - what happens if the units are cooling and then the DHW program starts? 

This will be heat pump and install dependant, but for me with ecodan 8.5kw with 2 zones (ufh gf, FCU FF) it works well enough 

3 port Diverter valve switches before any hot water hits the pipework, but means the UVC gets an initial slug of cold water before staring to heat.  At the end of the cycle it's a bit more issue as a slug of hot water gets into the FCU and can cause unpleasant warm air to blow into the bedrooms mid sleep. Simple controls don't work well for this as system is calling for cold, I use sensors on the pipe to detect the warm water and shut off the FCU fan and close zone actuators to the FCU (this means if the loft supply air is cooler than bedroom I can keep blowing that in even while the warm slug passes around).

 

A neat thing is because I have glycol free system in winter the freeze protect keeps slightly cool water circulating, the same sensors see that cool water and route it to the FCU for "free" bedroom cooling even when the system is otherwise in heating mode. (Otherwise our bedrooms still get too warm even when subzero outside...)

 

[G and J]

16 minutes ago, joth said:

(Otherwise our bedrooms still get too warm even when subzero outside...)

That’s the bit we are worried about.

 

18 minutes ago, -rick- said:

I would assume that if the water circuit diverts to DHW then the flow through the fan coil would stop.

Others on here having described using pipe temperature sensors to control the fan on the Fancoil in what sounds like a relatively simple and elegant set up.   I think our FC will be used for cooling only, in which case the fane will only come on if the room controller says ‘cool me’ and the pipe sensor says ‘I’m just soooo cool’.

 

Hopefully that will mean that the ‘burp’ of unwelcome hot or cold from the FC will be minimised.  

[G and J]

22 minutes ago, joth said:

the UVC gets an initial slug of cold water before staring to heat

Ouch.   Hadn’t thought of that.  I’m going to have a long pipe run from ASHP to UVC so that might require some thought.
 

As it will only happen when I need cooling - therefore on warm days - maybe it’s not an issue but a simple delay on the 3 port valve might sort it.

[joth]

11 minutes ago, G and J said:

Ouch.   Hadn’t thought of that.  I’m going to have a long pipe run from ASHP to UVC so that might require some thought.
 

As it will only happen when I need cooling - therefore on warm days - maybe it’s not an issue but a simple delay on the 3 port valve might sort it.

I don't think it's worth trying to fix this. Without having a 4 pipe ASHP then it's inherently a bit wasteful to switch the primary circuit from cold to hot and back again. Either you nick energy from the uvc to ramp up the switch over, or wait longer having the ASHP do it all, the electricity usage will net out about the same.

To avoid switching, As we use ASHP almost exclusively during octopus overnight cheap rate, on really hot days I have it just stay in cooling mode all the time and do DHW from the immersion as this can happen in parallel, and on cheap rate is still good value. 

Also, the cooling is only really needed in the night (for bedrooms) so in can blast dhw reheat off PV+ASHP midday. 

I use Loxone to decide and it's fairly complex (but all just optimisation layer,  things tick along acceptably even on default settings)