OK some fan coil unit questions

[LnP]

9 minutes ago, JohnMo said:

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.

Sorry I think I'm missing something .... so regardless of the position of your summer/winter switch, when there's a call for heat from the DHW, the ASHP automatically switches from cooling to heating?

[Dave Jones]

8 hours ago, LnP said:

Sorry I think I'm missing something .... so regardless of the position of your summer/winter switch, when there's a call for heat from the DHW, the ASHP automatically switches from cooling to heating?

 

We have ours set very very simple. Dial in a temp you want and leave it on auto. in our case we chose 16C and if its above this it will cool if its below it will heat. DHW will override this depending on how you set it.

[JohnMo]

8 hours ago, LnP said:

. so regardless of the position of your summer/winter switch, when there's a call for heat from the DHW, the ASHP automatically switches from cooling to heating?

Correct

[Nic]

On 25/08/2024 at 18:51, 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.

Can I ask what fan coils you’re using please 

[JohnMo]

1 hour ago, Nic said:

Can I ask what fan coils you’re using please 

I have one and it's a Myson iVector 120, 4 pipe, so has two heat exchangers (normally one for heat, and one for cooling) but have these are piped in series, so both are always engaged allow me to heat at much lower temps.

[LnP]

8 hours ago, JohnMo said:

... 4 pipe, so has two heat exchangers (normally one for heat, and one for cooling) but have these are piped in series, so both are always engaged allow me to heat at much lower temps.

The 4 pipe has two coils and the 2 pipe has one.... so are you saying that the 4 pipe, in total has more coil, a larger heat exchanger i.e. they didn't just cut the 2 pipe in half to make a 4 pipe?

[JohnMo]

51 minutes ago, LnP said:

The 4 pipe has two coils and the 2 pipe has one.... so are you saying that the 4 pipe, in total has more coil, a larger heat exchanger i.e. they didn't just cut the 2 pipe in half to make a 4 pipe?

Looking at the data sheet

The 4 port cooling capacity is only slightly lower than the 2 port - about 5%. The heating capacity is 30% lower. So unlikely to be just cut in half.

[Dave Jones]

whats the point of having cooling and heating rads ? Not like they are going to be used at same time ?

[JohnMo]

30 minutes ago, Dave Jones said:

whats the point of having cooling and heating rads ? Not like they are going to be used at same time ?

Fan coils are designed really for commercial. A 4 port configuration is for different heat and cooling plant. Not really for a domestic setting where heat and cooling is provided by an ASHP.

[garrymartin]

To add to JohnMo's comment, it's generally because in a commercial context (think hotel) different rooms might want to be cooled or warmed independently. By having four pipes / two coils, the entire complex can maintain a cooling pipe run and a heating pipe run, and then the individual units can be set to either provide heating or cooling dependant on the occupant wishes by using either the heating pipes/coil or the cooling pipes/coil.

 

As he mentions, with a single ASHP, you can only either cool or heat - you can't do both at the same time.

 

The following text is in my notes by way of example;

 

"Two-pipe systems are less flexible than a four-pipe system.  The entire building is in either heating mode or cooling mode.  The changeover from heating to cooling or vice versa is made manually, and there is always the possibility that unusual weather patterns might cause some occupant discomfort.  Overall, the majority of the buildings on campus are on a two-pipe system.  This means when winter starts to set in, the two-pipe system must be switched from cold water to hot water.  If the weather changes and it warms up for a few days, the occupants of a two-pipe building could become uncomfortable.  The building system could then be switched back to cold water, but the manual switchover requires a couple of days.  By the time this is accomplished, the weather could cool off again.  So as you can see, when it comes to heating and cooling a space with a two-pipe system, especially in our fluctuating Kentucky weather, it is a guessing game."