Flow rates for Carpet, Wood ,Concrete and Tiles

[Ben 64]

Hi Everyone,

 

Hoping you can offer some

guidance. I’ve just built a Barn with Heatmiser underfloor heating everywhere (no radiators) .

All powered by an source heat pump.

 

I have the length of my pipes and currently all the flow rates are set by default to 1.5. ( for the house to not feel chilly the flow temp needs to be at 44-46, was on 50 the other day when we were at -5/-7)

 

I have read up about the loop length  needing to be divided by 40 to a obtain  the flow rates, I was just wondering if that’s set in stone for all types of floor etc or should I be having less or more flow rates dependant on the floor type?

( As I have three rooms that are carpet, bathrooms are tiles and everywhere else is concrete floor.)

 

And does it matter how far away the room is from the plant room?

 

Thanks for your help 

[IanR]

Flow rates are not set in stone so you can adjust these to suit your installation. But I'd check a few basics first.

45° is a high flow temp for UFH via heat pump. Do you know the return temp? Are you leaving the heat pump on for long periods or are you using it like a gas boiler, ie. trying to warm the house just during occupied periods?

What's your floor build up? and pipe spacing?

[JohnMo]

The lower the flow rate, the higher the delta T and least amount of heat from the floor.  So you end with high flow temps.

 

I have Salus self regulating actuators on three of my loops with flow temp below 30 the DT is 4 and over 30 its 7. These loops are basically 100m and the flow rates are 2.5l/min. The other 4 loops are just adjusted to give the temp in the the other rooms that I want.  So bedrooms are cooler, ensuite is warmer.

 

As said 45 flow temp is hot, 1.5 l/min is low, unless you loops are short. Lower the temp considerably and up the flow rates and run for longer.  This help CoP.

[Ben 64]

Thank you for your replies.

Currently I’m running it more like a conventional heating.

on 3 hours in the early morning and 4 hours in the afternoon for it to warm up when we arrive back home.

 

When a Mitsubishi engineer came out he was surprised at how efficient it all was- as it was reading 3.8?

 

If I had the pump on all the time, wouldn’t it cost me more electricity/money?

 

I don’t know the pipe spacing but I do have this from the installation company .

 

When I tried a lower temperature the house wasn’t warm enough

 

 

[JohnMo]

1 hour ago, Ben 64 said:

If I had the pump on all the time, wouldn’t it cost me more electricity/money?

The simple maths

 

For a given external and internal temperature, the heat input will match the heat losses.

 

With a heat pump the lower the flow temp the better the CoP.

 

I have a full set Midea performance data so will use that. For a 5 deg day

 

So let's do 7 hours at 45 degs, so about 5.51kW X 7 = 38.6kWh of heat into the house, CoP of 3.27, so an electrical input of 11.8kWh.

 

Spreading the heat over 24 instead of 7.  38.6/24=1.6kWh

 

However the minimum output of the heat pump is 1.988kW.  So run time would be 19.4 hrs. (38.6/1.988) instead of 24.

 

Flow temp is now 30, CoP is now 5.23 and electrical input 380W.  19.4 hrs X 380W = 7.38kWh

 

So 38% less electrical use for the same heat. So no it won't cost you more money.

 

That's why they make a big thing about weather compensation.

 

 

 

[Ben 64]

33 minutes ago, JohnMo said:

The simple maths

 

For a given external and internal temperature, the heat input will match the heat losses.

 

With a heat pump the lower the flow temp the better the CoP.

 

I have a full set Midea performance data so will use that. For a 5 deg day

 

So let's do 7 hours at 45 degs, so about 5.51kW X 7 = 38.6kWh of heat into the house, CoP of 3.27, so an electrical input of 11.8kWh.

 

Spreading the heat over 24 instead of 7.  38.6/24=1.6kWh

 

However the minimum output of the heat pump is 1.988kW.  So run time would be 19.4 hrs. (38.6/1.988) instead of 24.

 

Flow temp is now 30, CoP is now 5.23 and electrical input 380W.  19.4 hrs X 380W = 7.38kWh

 

So 38% less electrical use for the same heat. So no it won't cost you more money.

 

That's why they make a big thing about weather compensation.

 

 

 

Wow! That’s quite amazing.

 

I will have to change How my zones are setup then.

 

How have you set yours up?

 

As this is how it’s setup for the kitchen, lounge  , utility area as its setup on the one zone on my Heatmiser app.

Have also attached a heat graph ( the kitchen warms up when the sun is out due to the glass )

 

and the estimated consumed energy summary from my Mitsubishi App for the last 5 days.

Your help is really appreciated 

[JohnMo]

36 minutes ago, Ben 64 said:

How have you set yours up?

 

I've played with many options.  My system is heat pump ready, but on a gas boiler.

 

Started last year with every room as a zone, a buffer that wasn't correctly plumbed, lots of short cycling.  Slowly refined it, testing gas usage, flow temperature and comparing against a heat meter.

 

Have tried batch heating, at high flow temps, fixed medium flow temp controlling heating on thermostats, and weather compensation.

 

Some finding

If you have some zones on and others off, in my house the flow temp is generally 2 degrees hotter, for the same overall house temp.  I have run the buffer on a thermostat and the UFH on a fixed flow temp, gas to heat efficiency 95%.

 

Also found that cheaper Reliance mixer isn't as good as an Ivar one.  The benefit of the Ivar is the ability to adjust internal recycling proportion, so fine tuning is better.

 

Basically now set up on full weather compensation, through Ivar mixer.  All room thermostats moved to about 21 degrees (out of the way). Set flow temp to give main room 19 degrees and bedrooms 17/18 (Adjusted flow rate). Compensation curve varies between 25 at 10 degrees outside to 32 degs at -9 deg outside.

 

Gas to heat efficiency now running at 102%.  Have now added a nighttime setback of 2 degs for 7 hours to see how that goes.

 

Currently I do not need the thermostats, they are just there to save decorating.

[Ben 64]

14 hours ago, JohnMo said:

The simple maths

 

For a given external and internal temperature, the heat input will match the heat losses.

 

With a heat pump the lower the flow temp the better the CoP.

 

I have a full set Midea performance data so will use that. For a 5 deg day

 

So let's do 7 hours at 45 degs, so about 5.51kW X 7 = 38.6kWh of heat into the house, CoP of 3.27, so an electrical input of 11.8kWh.

 

Spreading the heat over 24 instead of 7.  38.6/24=1.6kWh

 

However the minimum output of the heat pump is 1.988kW.  So run time would be 19.4 hrs. (38.6/1.988) instead of 24.

 

Flow temp is now 30, CoP is now 5.23 and electrical input 380W.  19.4 hrs X 380W = 7.38kWh

 

So 38% less electrical use for the same heat. So no it won't cost you more money.

 

That's why they make a big thing about weather compensation.

 

 

 

I have increased the flow rates to as close as 2.5 as I can. One bedroom can’t go that high as it loosens too much and pops in the air so fluid goes everywhere.

 

From looking at the smart meter- having the flow temp on 35 compared to 44-45 doesn’t seem to be much less in KW and if it doesn’t heat up the house as much and had to be on longer It won’t be as effective .
Maybe as mine is all electric with no gas and radiators it’s different to yours?

 

Will see what the pump says in 5 days time and post my findings 

 

Thanks for your help

[IanR]

17 hours ago, Ben 64 said:

Currently I’m running it more like a conventional heating.

on 3 hours in the early morning and 4 hours in the afternoon for it to warm up when we arrive back home.

 

With a heat pump you need to have the heating system running for much longer periods, this allows you to reduce the flow temp (once the slab is up to temp) and run the heat pump more efficiently. Your heat pump is only capable of putting around 1/3rd of the energy that a gas boiler can, into the UFH, so it needs to run at least 3 times as long to put the same energy into the house. Run it for even longer and you can run at lower temps and improve the efficiency.

 

My system is heated via a heat pump with a flow temp of 32°C/33°C and a return temp of around 28°C, once everything is up to temp. The heat pump is allowed to run for up to 15 hours. It doesn't actually run for all that time, it just comes on and off during that period, when it needs to. At the start of the heating season though, it needs to run almost constantly for the allowed period for a couple of days to "charge" the slab up, but once up to temperature the slab stays a pretty a constant 21°C to 22°C at the surface. For heating, at the low flow temps, the heat pump is running at a COP of over 5. For hot water though the flow temp is 50°C, which drops the average COP a little.

 

If you are struggling with getting your house up to temp, I'd let it run 24 hours a day until the target temp is met, then reduce the flow temps until you are in the 35°C to 40°C range where the heat pump efficiency will have improved, and then see if there's some "head room" in your system to start to restrict the number of hours the heat pump can run for.
With regards to flow rates, this is more about balancing the system and getting each zone to it's target temp, at the same time.

[Ben 64]

The outside temperature has definitely helped the house temperature- but the readings are showing , that the raising of the flow rates and lowering of the flow temperature has helped the energy consumption of the unit.
The flow temperature is currently set to 35c.

The house isn’t feeling cold either.

 

I’m not using a timer and just have the thermostat set to 22 for the kitchen and 21 for the bedroom

 

Thank you for your help, it’s much appreciated