Underflow flow temps.

[Fly100]

Hello all,

After your thoughts on on Underfloor water temps. Im currently running at 40c but this is resulting in long warm up times. ( due to weather and house make up its only on once everyday). However if I was to turn it to 45c warm uptimes decrease obviously but there is extra energy being used to produce the extra temprature.

 

Which is the most efficinet Im on an Oil boiler with no buffer tank and my return temps are well below the 47c mark for the boiler to condensate.

 

Thanks in advance.

FLY

[ProDave]

The UFH temperature should be regulated by a blending valve on the manifold, not by turning down the boiler temperature.

 

You really want to run UFH for longer at a lower temperature.  i.e run it all day but at a lower temperature.  That should not incrrease fuel usage, if it's been done right room thermostats will turn the heating off when the rooms reach the required temperature.

[Fly100]

4 minutes ago, ProDave said:

The UFH temperature should be regulated by a blending valve on the manifold, not by turning down the boiler temperature.

 

You really want to run UFH for longer at a lower temperature.  i.e run it all day but at a lower temperature.  That should not incrrease fuel usage, if it's been done right room thermostats will turn the heating off when the rooms reach the required temperature.

 

I should have noted that is the Manifold Mix Valve Temp not the boiler flow temp. As an oil boiler does not modulate its output I wondered if this changed the utilization.

[A_L]

2 hours ago, Fly100 said:

However if I was to turn it to 45c warm uptimes decrease obviously but there is extra energy being used to produce the extra temprature.

 

The higher flow temperature means that the rate at which the floor can accept energy is higher so assuming you do not turn it up to far, to significantly reduce condensing, there will be little loss of efficiency. There will also be a beneficial effect on boiler cycling, the burner will stay on longer and the inefficiencies associated with burner start-up/shutdown will be reduced. The boiler will probably have an output greater than the ability of the floor to accept energy so you will be unlikely to eliminate cycling entirely.

 

Therefore in conclusion you want the lowest flow temperature which does not cause rapid burner cycling. Is the 47°C for condensing a manufacturer recommendation? I ask as for gas boilers 57°C is usually considered the maximum return temp to cause condensing?

[AliG]

59 minutes ago, ProDave said:

You really want to run UFH for longer at a lower temperature.  i.e run it all day but at a lower temperature.  That should not incrrease fuel usage, if it's been done right room thermostats will turn the heating off when the rooms reach the required temperature.

 

I have experimented with this and continue to do so.

 

On the one hand, previously I set my heating back 2-3C during the night and it was running for a long time in the mornings to get back to temperature. Having changed the night time set back to 1C, which basically means the heating comes on occasionally during the night if it is very cold it seemed to get more efficient. So running a more constant temperature seems more efficient.

 

But during the day I was running lower flow temperatures for longer periods. Rooms heated up at quite different rates and the boiler would be running off and on for short periods for 3 or 4 hours.

 

I have raised the flow temperatures so that the house heats up faster in the morning, trying to run al the zones at once. This reduces short cycling of the boiler. As the floor gets warmer, the house then stays a nice temperature most of the day and the heating only comes back on if it is quite cold.

 

This seems to save on gas usage.

 

So some ways running a constant temperature helps and some weight running a higher flow temperature and shorter runs on the boiler helps.

 

I suspect that a gas boiler that is oversized for heating requirements may work better with a high flow temperature for short periods than an ASHP, but that is a guess.

 

Maybe as an experiment I should try not setting the temperature back during the night and just leaving the heating on 24 hours a day, that is the one thing I have not tried yet.

 

The trouble is there are a lot of settings to change to try these things and then you need similar weather to compare heating usage.

 

I have been monitoring gas usage the last few days after making a few changes. I will try turning up the nighttime temp tonight and see what happens.

 

 

 

 

Edited November 13, 2020 by AliG

[Fly100]

47 minutes ago, A_L said:

 

 

 

Therefore in conclusion you want the lowest flow temperature which does not cause rapid burner cycling. Is the 47°C for condensing a manufacturer recommendation? I ask as for gas boilers 57°C is usually considered the maximum return temp to cause condensing?

I was always under the impression its was 55c, but it would seem 47c for oil boilers. I will be happy to be corrected if incorrect.

[Fly100]

35 minutes ago, AliG said:

 

I have experimented with this and continue to do so.

 

On the one hand, previously I set my heating back 2-3C during the night and it was running for a long time in the mornings to get back to temperature. Having changed the night time set back to 1C, which basically means the heating comes on occasionally during the night if it is very cold it seemed to get more efficient. So running a more constant temperature seems more efficient.

 

But during the day I was running lower flow temperatures for longer periods. Rooms heated up at quite different rates and the boiler would be running off and on for short periods for 3 or 4 hours.

 

 

 

 

 

 

My house temps only drop 2 or 3 degrees over night depending on outside temps and wind direction. We are completley exposed to the West. Id dropped the temp down to 40c as we only need a small uplift in temps, thinking it would reduce the oil consumption slightly.

[AliG]

2-3C is decent drop overnight.

 

In that case it might be better to set the thermostat back one degree during the night which will have the heating coming off and on all night but not running so hard to get back up to temperature in the morning.

 

Ultimately I think all you can do is try different permutations and see which is most efficient in real use. this does require a lot of trial and error.

 

One thing I found was that in rooms with wooden floors 40C wasn't getting the floor warm enough to heat up the room. The floor might only come up to 22C and then the heating might be on for four or five hours to warm the room up. I turned up the flow to 44ish so that the floor temp was 24-25C and the room heated up in an hour or two.

 

Now it might be in this situation you could run a lower floor temperature constantly versus a higher floor temperature for an hour or two. My feeling is that there is a point where the heating ends up being on considerably longer at only a slightly lower temperature so it may not be more efficient.

[OldSpot]

On 13/11/2020 at 10:35, Fly100 said:

Hello all,

After your thoughts on on Underfloor water temps. Im currently running at 40c but this is resulting in long warm up times. ( due to weather and house make up its only on once everyday). However if I was to turn it to 45c warm uptimes decrease obviously but there is extra energy being used to produce the extra temprature.

 

Which is the most efficinet Im on an Oil boiler with no buffer tank and my return temps are well below the 47c mark for the boiler to condensate.

 

Thanks in advance.

FLY

Fly,

What oil boiler are you using?

I seem to remember Grant saying 40C is the lowest return temp to avoid corrosion?

[Fly100]

Worcester Bosch,

 

Happy to hear any differnet views as im reviewing things at the minute.

 

FLY

[Temp]

On 13/11/2020 at 10:35, Fly100 said:

However if I was to turn it to 45c warm uptimes decrease obviously but there is extra energy being used to produce the extra temprature.

 

Yes but for less time. Overall if the thermostat and time clocks aren't changed the bills shouldn't increase because the heat losses should stay the same.

 

In practice if the floor is hotter there might be increased losses into the ground.