ASHP & sizing fan coil units

[Fenton H]

Hi I found this group forum when looking for a reliable way to size fan coil units (FCUs).  I'm about to start a major renovation of our house in the south east of England which will include an ASHP for heating and cooling.  Does anyone know whether the FCU heating outputs quoted by suppliers are normally about right for an ASHP operating at 40-45C?  The house will be close to passive standards so I'm not too concerned about being exact, but I don't want to seriously oversize the kit. Same for cooling, I'm not too concerned as it's only a secondary consideration and I'm assuming that if the FCUs are right for heating they should be fine for cooling.  It looks like I might have to start getting into the detail and estimating the temperature drop across the FCUs to size them - can anyone with ASHP experience please advise a typical temperature difference between the ASHP water inlet and outlet when operating at efficient temperature, say 45C ASHP outlet temp? 

 

 

[ProDave]

I can't contribute to the question, but I looked for a couple of FCU's a while back (to add cooling to our house, UFH used for heating) and found them both hard to find, and very expensive for what is a very basic piece of kit from a technical viewpoint.  So if you have found a good cheap source please share.

[jack]

1 hour ago, Fenton H said:

.. and I'm assuming that if the FCUs are right for heating they should be fine for cooling.  

 

Not quite. I believe the ones designed for cooling have a condensate try and drain. I believe the ones that are okay for cooling will be fine for heating, but not necessarily the other way around. 

 

If you're talking about heating/cooling capacity, I think it's probably the other way around (ie, you need more heating capacity than cooling capacity, in general). Personally, I'd be concerned about dry air if this is to be your sole method of heating the house. 

[Nickfromwales]

1 hour ago, Fenton H said:

I'm assuming that if the FCUs are right for heating they should be fine for cooling

Ahhh, the A-word  

You will need to confirm that the unit has a condensation trap and drain point, as when cooling is used it’ll likely produce condensation. That also means a gravity waste pipe to drain that away in each location. 

Likewise, please keep us informed as an all-in-one solution is difficult to find in anything near a decent price range. Check out BPC’s website for  some examples of bare units with which to construct such a setup. 

[TonyT]

And or a condensate pump 

[Fenton H]

Thanks for all the info.  I'll definitely update with prices if I manage to find any decent units.

 

I'm also hoping that even if FCUs are a bit expensive it will compare favourably with the cost of installing UFH.  And in any case there's no other way to cool using an air-to-water ASHP is there?  I'd be interested if anyone can recommend other options for cooling using air-to-water (cooling via UFH isn't really an option in the bedrooms as they'll be carpeted). I'm not keen on air-to-air as it's outside of RHI payback, doesn't provide hot water,  I don't want 2 separate ASHP systems etc.

[jack]

1 hour ago, Fenton H said:

I'm also hoping that even if FCUs are a bit expensive it will compare favourably with the cost of installing UFH.  And in any case there's no other way to cool using an air-to-water ASHP is there?  I'd be interested if anyone can recommend other options for cooling using air-to-water (cooling via UFH isn't really an option in the bedrooms as they'll be carpeted). I'm not keen on air-to-air as it's outside of RHI payback, doesn't provide hot water,  I don't want 2 separate ASHP systems etc.

 

I use an ASHP to heat and cool our downstairs floors. They're polished concrete, so it's really effective (it's like walking into a cave in the middle of summer - on a really hot day the kids come inside and lie down on it to cool down quickly!) The one carpeted room downstairs doesn't get heated or cooled anywhere near as well as the bare floors, so I think you're right to be concerned about UFH upstairs if you're having carpets.

 

If I were doing this again, I think I'd go for tiled floors in bedrooms, and put down large rugs in the colder months. You'd then just need to heat enough to keep the chill off in winter, but you'd have the full effect of UFC for summer. The alternative would be an air conditioner for summer.

 

Depends on what your insulation levels are like, and what temperature you like your bedrooms, but we're happy with no heating in the bedrooms.

 

[Fenton H]

On 25/02/2021 at 18:09, ProDave said:

I can't contribute to the question, but I looked for a couple of FCU's a while back (to add cooling to our house, UFH used for heating) and found them both hard to find, and very expensive for what is a very basic piece of kit from a technical viewpoint.  So if you have found a good cheap source please share.

Well I found a nice wall mounted model (panasonic), there's some really good sizing data for them in the specs, such as here:

 https://www.seconrenewables.com/panasonic-aquarea-air-radiator-4237-p.asp

You're right that they are a bit expensive (£600 for the small model- £700 for the bigger one on https://www.easyheatpumps.com/cart/)  - but they're designed for heating and cooling bedrooms, and look pretty easy to install.  As my only other option is UFH, which wont cool very well, I can justify the cost but if its an additional unit on top of UFH I can see it's a bit prohibitive.

[ProDave]

1 minute ago, Fenton H said:

Well I found a nice wall mounted model (panasonic), there's some really good sizing data for them in the specs, such as here:

 https://www.seconrenewables.com/panasonic-aquarea-air-radiator-4237-p.asp

You're right that they are a bit expensive (£600 for the small model- £700 for the bigger one on https://www.easyheatpumps.com/cart/)  - but they're designed for heating and cooling bedrooms, and look pretty easy to install.  As my only other option is UFH, which wont cool very well, I can justify the cost but if its an additional unit on top of UFH I can see it's a bit prohibitive.

That is my issue.  £600 for a box containing a water to air heat exchanger, a fan, and a drip tray to collect any condensation.  For that money, you can buy a complete air to air ASHP aka an air conditioning unit.

 

[Fenton H]

I agree ProDave, mad price.  At least there's possibly less installation work, no additional compressor outside and the controls are included/integrated (no additional remote to lose or eat up those AAA batteries ?).  I've also come across various half decent looking 'refurbed' wall hung models (radiator type heat/cool similar to the panasonic aquarea) on sites such as ebay for 250 quid.  I haven't looked at them in detail as not something I'd use for our new-build but might be worth considering as a low cost option?

Edited February 27, 2021 by Fenton H
typo

[volcane]

@jack
how do you control your slab cooling? I'm about to install a 8kW Daikin LT split ASHP but both supplier and installing plumber are very dismissive of the cooling ability, despite what the Daikin literature says. I have a fully tiled ground floor.

Is it as simple as, switch the ASHP to cooling and set the thermostats to the desired temperature and let the ASHP reach that?

[jack]

2 hours ago, volcane said:

how do you control your slab cooling? ...

Is it as simple as, switch the ASHP to cooling and set the thermostats to the desired temperature and let the ASHP reach that?

 

I should probably use a thermostat, but I just run it open circuit at 16 deg C, and switch it into cooling mode manually when needed. Usually only bother if we have a run of hot weather predicted, as it takes a while for the house to get hot.

 

If you plan to use a thermostat, bear in mind that when cooling you'll need to have it trigger when the temperature goes above a setpoint, whereas for heating it's the other way around. I don't know whether some thermostats have N/O and N/C outputs so you could have one pair connected for heating and the other for cooling, and then just change the mode at the ASHP on a seasonal basis. Alternatively, use a separate cooling thermostat.

 

2 hours ago, volcane said:

I'm about to install a 8kW Daikin LT split ASHP but both supplier and installing plumber are very dismissive of the cooling ability, despite what the Daikin literature says. I have a fully tiled ground floor.

 

What's their basis for saying this? I only have a 5kW unit (which has even lower cooling capacity) but I wouldn't be without it during hot periods in summer. It's extremely pleasant walking around on cool floors when it's really hot outside. People who come into our house for the first time at times like this are always stunned at how pleasant it is. It's a very different feeling to cooling via air conditioning.

 

[Hobbiniho]

I have the panasonic air rads and find they work quite well, although i wouldnt want them in a bedroom due to the fan noise, worth noting that they have a minimum flow temp of 30degrees in heating mode, as has been said they are expensive for what they are. i was also looking at dimplex smartrads but decided to stick with the panasonic to match my heatpump