Interesting experiment

[Beelbeebub]

Over the current cold snap I've had 2 flats empty.

 

As an experiment I turned the boiler flow down to 40.

 

Bith flats are single glazed and solid walled with no additional insulation.

 

One was a mid level flat (ie between occupied flats) and the other was ground floor (suspended floor, no insulation beyond underlay and carpet)

 

Both flats one bed around 80m2

 

The rads in the flats were fairly good. We tended to bung in big k22s unless there was an issue with depth from wall. The pipework is a mishmash of 15, 22 copper with some speed fit here and there. Basically you big standard victorian flat/terrace that has been upgraded piecemeal over the decades.

 

Both easily (as in the boiler was cycling) maintained a steady 18C through the cold weather (-4C lows, 2C day)

 

An interesting, albeit small, datapoint in the "most British homes will need massive upgrades" and "you can't use a heat pump on an old property" debate.

Edited January 9 by Beelbeebub

[SteamyTea]

Keep them empty and I shall come over and put some decent logging in.

Then I can publish a paper about them, mostly at your expense.

[marshian]

3 hours ago, Beelbeebub said:

Over the current cold snap I've had 2 flats empty.

 

As an experiment I turned the boiler flow down to 40.

 

Bith flats are single glazed and solid walled with no additional insulation.

 

One was a mid level flat (ie between occupied flats) and the other was ground floor (suspended floor, no insulation beyond underlay and carpet)

 

Both flats one bed around 80m2

 

The rads in the flats were fairly good. We tended to bung in big k22s unless there was an issue with depth from wall. The pipework is a mishmash of 15, 22 copper with some speed fit here and there. Basically you big standard victorian flat/terrace that has been upgraded piecemeal over the decades.

 

Both easily (as in the boiler was cycling) maintained a steady 18C through the cold weather (-4C lows, 2C day)

 

An interesting, albeit small, datapoint in the "most British homes will need massive upgrades" and "you can't use a heat pump on an old property" debate.

 

Be interested on how much the boilers cycled - my bet would be not much more than they would with a flow temp of 50 and a room temp target of 20.

 

It must be a fairly decent boiler to get down to 40 flow temp setting - My old Glow worm gas boiler had a minimum of 39 - that was the lowest temp it could be set too but damn thing wouldn't stop cycling constantly unless you put the flow temp up to 45 then it could just about cope with restarts.

[andyj007]

surely you need to have the boiler on timer for 10mins an hour  max , as this is all the ashp would run at max for as it goes through defrost mode twice an hour and only just reaches ia 35 degree high point twice for 5mins each time i that hour..  this is why radiators and old houese struggle ..  whilst a great desiged house with Under floor , can just about maintain a half decent indoor 20-21 temp at those flow rates,, an old house  one wth small small rads has zero chance .. IMO  

Edited Friday at 07:02 by andyj007

[ProDave]

1 hour ago, andyj007 said:

surely you need to have the boiler on timer for 10mins an hour  max , as this is all the ashp would run at max for as it goes through defrost mode twice an hour and only just reaches ia 35 degree high point twice for 5mins each time i that hour.

That is most definitely not normal behaviour for an ASHP. If it is defrosting that often there is something wrong.

[Beelbeebub]

2 hours ago, andyj007 said:

surely you need to have the boiler on timer for 10mins an hour  max , as this is all the ashp would run at max for as it goes through defrost mode twice an hour and only just reaches ia 35 degree high point twice for 5mins each time i that hour..  this is why radiators and old houese struggle ..  whilst a great desiged house with Under floor , can just about maintain a half decent indoor 20-21 temp at those flow rates,, an old house  one wth small small rads has zero chance .. IMO  

Boiler was running about 20-30 minutes per hour. Temperature rose fairly quickly showing that the heat input from the 40C rads was well above heat loss. I have no doubt we could reach 20-21C at less than 45C in these conditions and the heavy construction means the property wouldn't cool significantly during any defrost cycles. The takeaway is the radiator size is the important factor not the construction.

 

 

 

 

 

Edited Friday at 09:50 by Beelbeebub

[SteamyTea]

23 minutes ago, Beelbeebub said:

heavy construction means the property wouldn't cool significantly during any defrost cycles

Makes no difference, it is the overall thermal conductivity of the building that governs the heat loss times.

[JohnMo]

Just to give you area of what happens during a defrost. This mine

 

So green is the return temp, that drops around 3 degs through the defrost cycle. The flow temp (red) drops a good 17 degs. However the time period is 5 mins in total. Run time between defrosts being about 1hr and 10 mins.

Edited Friday at 10:39 by JohnMo

[Beelbeebub]

3 hours ago, SteamyTea said:

Makes no difference, it is the overall thermal conductivity of the building that governs the heat loss times.

It governs the heat loss but the drop in internal temperature is also affected by the thermal mass.

 

Stop heating a tent and it gets cold almost immediately.

 

Stop heating granite cottage and you won't notice for an hour or so.

 

It's exactly why the HPs need a certain system volume. If thry only had 10 liters they might not be able to defrost before thry froze the water.  If they have 200l the water temp will barely dip.

[SteamyTea]

1 hour ago, Beelbeebub said:

Stop heating a tent and it gets cold almost immediately.

 

Stop heating granite cottage and you won't notice for an hour or so.

Really.

 

Nylon is a typical tent material, it has a thermal conductivity of 0.25 W.m^-1.K^-1.

Granite is 2 W.m.^-1.K^-1.

Say the tent material is 0.001m thick and the granite wall is 0.6m thick.

 

Nylon

U-Value = 1(L/k) = 1/(0.001 [m] / 0.025 [ W.m^-1.K^-1]) = 250 W.m^-2.K^-1

 

Granite

U-Value = 1(L/k) = 1/(0.6 [m] / 2 [ W.m^-1.K^-1]) = 3.3 W.m^-2.K^-1.

 

It is the thermal conductivity that is important.

 

To emphasise this more, think about the units involved.

Thermal losses are measured in watts [W], which is a joule per second [J.s^-1), so is energy divided by time.

 

Specific Heat Capacity is a measure of energy stored, joules [J] and has nothing to say about time.

 

Make a tent out of 0.6m thick nylon walls and the U-Value will be 0.4 W.m^-2.K^-1.

 

Looking at the mass, Nylon is 1150 kg.m^-3, granite is around 2700 kg.m^-3.

So a granite has a density of 2.35 that of nylon. So even of the building was made from 0.6m thick nylon, it would still be lighter.

 

If just adding mass to a building's external structure reduced the thermal losses, life would be easy, just pile mud up to the top of the chimney and be done with it, and call it a cave.

 

[Beelbeebub]

36 minutes ago, SteamyTea said:

Really.

 

Nylon is a typical tent material, it has a thermal conductivity of 0.25 W.m^-1.K^-1.

Granite is 2 W.m.^-1.K^-1.

Say the tent material is 0.001m thick and the granite wall is 0.6m thick.

 

Nylon

U-Value = 1(L/k) = 1/(0.001 [m] / 0.025 [ W.m^-1.K^-1]) = 250 W.m^-2.K^-1

 

Granite

U-Value = 1(L/k) = 1/(0.6 [m] / 2 [ W.m^-1.K^-1]) = 3.3 W.m^-2.K^-1.

 

It is the thermal conductivity that is important.

 

To emphasise this more, think about the units involved.

Thermal losses are measured in watts [W], which is a joule per second [J.s^-1), so is energy divided by time.

 

Specific Heat Capacity is a measure of energy stored, joules [J] and has nothing to say about time.

 

Make a tent out of 0.6m thick nylon walls and the U-Value will be 0.4 W.m^-2.K^-1.

 

Looking at the mass, Nylon is 1150 kg.m^-3, granite is around 2700 kg.m^-3.

So a granite has a density of 2.35 that of nylon. So even of the building was made from 0.6m thick nylon, it would still be lighter.

 

If just adding mass to a building's external structurereducedd the thermal losses, life would be easy, just pile mud up to the top of the chimney and be done with it, and call it a cave.

 

No, I'm not talking about the energy lost.

 

I'm talking about the temperature inside.

 

The high thermal mass of the building means the radiators being off for 5, maybe 10 minutes whilst the HP defrost results in a negligible drop in room temperature.

 

If the thermal mass was low, the room temp would drop much faster

 

Take a 2 liter coke bottle of air and a 2liter coke bottle of water outside on a cold night.

 

Which one stays warm the longest? They both have the same thermal conductivity and thus losses for a given dT.

[SteamyTea]

31 minutes ago, Beelbeebub said:

Take a 2 liter coke bottle of air and a 2liter coke bottle of water outside on a cold night

How, and where, is the energy lost to induce the temperature change in the fluid?

[Beelbeebub]

31 minutes ago, SteamyTea said:

How, and where, is the energy lost to induce the temperature change in the fluid?

I think we are at cross purposes here.

 

I am *not* disputing that the amount of energy lost during a given "radiators off" period is governed by the insulation levels of the building (the U value)

 

I'm simply pointing out that, in a heavy masonry building, the resultant drop in temperature due to that amount of energy being lost is negligible.

[SteamyTea]

2 minutes ago, Beelbeebub said:

think we are at cross purposes here.

Probably.

 

But mass, in itself, does not correlate to power.

 

There is a lot of misunderstanding and myths about heavyweight and lightweight construction.

Even when I have read papers about 'identical' house, with different construction methods, on closer inspection, they are not identical at all.

 

I once went to see a 'solar house' in St. Issy, it had a huge block of concrete inside to help stabilise the temperature.

This concrete was around the internal air temperature, so, at best, very little power delivery.

The 0.4m of polystyrene, and the 'Toblerone' shape would have made the biggest difference.

 

Adding 'thermal mass' sounds scientific, but as it cannot have meaningful units associated with it, it is just puff.

[Beelbeebub]

Agreed there is confusion but heavy masonry walls, especially external ones, do help stabilise temperature when the heat input (rads) is turned off for a period.

 

The big passive concrete block in the middle doesn't do much (as you say, it delivers very little power)

 

The same (or ideally greater) mass distributed in the walls and floor woukd stabilise the temperature more for a given insulation level.

 

If you had 2 hollow cubes.

 

One concrete with an insulation jacket and the other just the insulation (adjusted so U values were the same)

 

They are both at steady state (say 20C inside and 0C outside for 1kw input)

 

You then turn the heater off for 10 minutes.

 

The temperature in the concrete cube will fall less in the 10 minutes than the plain cube. Though the plain cube internal temp will also rise faster when the heating is restored.

[Beelbeebub]

I'm saying that my poorly insulated but heavy walled flats won't cool down any noticeable amount whilst the defrost cycle is occurring.

 

The only effect of defrost cycles would be to reduce the average power input. As long as that average power output is enough to maintain the desired temp there isn't a problem.

Edited Friday at 18:26 by Beelbeebub

[JohnMo]

4 hours ago, SteamyTea said:

Adding 'thermal mass' sounds scientific, but as it cannot have meaningful units associated with it, it is just puff.

Isn't thermal mass just another way of saying thermal inertia, which is defined by the heat capacity, so it does have SI units. The empty bottle of coke has the same heat capacity of air, so not much. The full of coke bottle has loads of heat capacity in comparison. 

 

You just don't like the term, but resistance is futile - life is too short move on.

 

A timber framed house insulated with PIR insulation has a good U value, so does one stuffed with cellulose. The cellulose is way more dense, has way more thermal heat capacity, by virtue of its density.

 

So if temperature within the insulated envelope are equal and you switch of the heating, the building with dense materials will be the one I will be in.

 

Example - We have a well insulated house and a well insulated summer house. All run from the same heating system, the summer house temp drops in the numbers of degrees, the house barely changes temp in the same time period. Heating up, summer house heats really quickly, just heating air, the house can takes hrs of heat to move it tenths of a degree.

 

One day of data top line is the house, bottom the summerhouse 

 

[marshian]

8 hours ago, SteamyTea said:

Really.

 

Nylon is a typical tent material, it has a thermal conductivity of 0.25 W.m^-1.K^-1.

Granite is 2 W.m.^-1.K^-1.

Say the tent material is 0.001m thick and the granite wall is 0.6m thick.

 

Nylon

U-Value = 1(L/k) = 1/(0.001 [m] / 0.025 [ W.m^-1.K^-1]) = 250 W.m^-2.K^-1

 

Granite

U-Value = 1(L/k) = 1/(0.6 [m] / 2 [ W.m^-1.K^-1]) = 3.3 W.m^-2.K^-1.

 

It is the thermal conductivity that is important.

 

To emphasise this more, think about the units involved.

Thermal losses are measured in watts [W], which is a joule per second [J.s^-1), so is energy divided by time.

 

Specific Heat Capacity is a measure of energy stored, joules [J] and has nothing to say about time.

 

Make a tent out of 0.6m thick nylon walls and the U-Value will be 0.4 W.m^-2.K^-1.

 

Looking at the mass, Nylon is 1150 kg.m^-3, granite is around 2700 kg.m^-3.

So a granite has a density of 2.35 that of nylon. So even of the building was made from 0.6m thick nylon, it would still be lighter.

 

If just adding mass to a building's external structure reduced the thermal losses, life would be easy, just pile mud up to the top of the chimney and be done with it, and call it a cave.

 

 

@SteamyTea mate never stop what you do - it's brilliant and 100% appreciated - from a maths perspective it's art

[SteamyTea]

5 hours ago, JohnMo said:

Example - We have a well insulated house and a well insulated summer house

They have different sizes, surface areas, form factors and volumes though.

 

When it comes to thermal effusivity, which is the product of specific heat capacity, density and conductivity, the materials hopium and unobtainium are often used as examples.

[Beelbeebub]

We are drifting away from the thread.

 

The point was; I had 2 unimproved victorian flats with reasonably (but not ludicrously) large radiators and was able to maintain a steady 18C in sun zero conditions with the boiler flow set to 40C.

 

This implies a heatpump could efficiently and cost effectively do the same.

 

There was a question about the defrost cycle which I believe would not impact the ability of the HP to maintain 18C.

 

My conclusion is (and I don't think this is controversial) the factor that dominates whether or not a HP can cost effectively a building is the emitter sizing and not the levels of insulation.

 

The insulation (heatloss) of a building dominates the sizing and hence costhence costatpump.

 

The emitters (rads etc) dominate the Scop and hence running costs.

 

(note dominate not exclusively control)

Edited Saturday at 08:56 by Beelbeebub

[JohnMo]

4 hours ago, SteamyTea said:

They have different sizes, surface areas, form factors and volumes though.

That is correct the summer house a near perfect cube, the house long tall thin box. House has nearly the perfect opposite of good form factor. Granted bigger volume. 

 

But you are missing the point (purposely I suspect). I will leave it there, it's diverting away from the thread.

 

4 hours ago, SteamyTea said:

materials hopium and unobtainium

My floor is full of it, so are your storage heaters, obviously.

[PhilT]

40 minutes ago, Beelbeebub said:

The point was; I had 2 unimproved victorian flats with reasonably (but not ludicrously) large radiators and was able to maintain a steady 18C in sun zero conditions with the boiler flow set to 40C. This implies a heatpump could efficiently and cost effectively do the same.

All true and you're preaching to the converted here, but amongst the general public, I worry about the ever increasing and ill informed adverse publicity especially in national media such as The Daily Mail, This Is Money etc. by people like Jeff Prestridge, who should know better. I wrote him a stinking email recently in direct response to one of his most recent articles - he writes such utter rubbish, but there is a serious concern that perception has gone too far already in the wrong direction

[IGP]

22 hours ago, Beelbeebub said:

We are drifting away from the thread.

 

The point was; I had 2 unimproved victorian flats with reasonably (but not ludicrously) large radiators and was able to maintain a steady 18C in sun zero conditions with the boiler flow set to 40C.

 

This implies a heatpump could efficiently and cost effectively do the same.

 

There was a question about the defrost cycle which I believe would not impact the ability of the HP to maintain 18C.

 

My conclusion is (and I don't think this is controversial) the factor that dominates whether or not a HP can cost effectively a building is the emitter sizing and not the levels of insulation.

 

The insulation (heatloss) of a building dominates the sizing and hence costhence costatpump.

 

The emitters (rads etc) dominate the Scop and hence running costs.

 

(note dominate not exclusively control)

Which is why I’ve come to the conclusion that we probably should be only recommending 300mm loft insulation, CWI (if have cavities wide enough) and upgrading to DG from SG for *most* properties, unless you happen to be doing more work anyway and can insulate more while there. New builds should be much higher standards. 
 

These are the highest impact per £ invested. And then HPs at <45c design flow temp as that is around at the point where SCOP for most HPs beats the spark gap and saves money for people (and be therefore can be seen as better, not just equal to gas).
 

But that’s just my rules of thumb. 

[Beelbeebub]

1 hour ago, IGP said:

Which is why I’ve come to the conclusion that we probably should be only recommending 300mm loft insulation, CWI (if have cavities wide enough) and upgrading to DG from SG for *most* properties, unless you happen to be doing more work anyway and can insulate more while there. New builds should be much higher standards. 
 

These are the highest impact per £ invested. And then HPs at <45c design flow temp as that is around at the point where SCOP for most HPs beats the spark gap and saves money for people (and be therefore can be seen as better, not just equal to gas).
 

But that’s just my rules of thumb. 

I agree reducing demand should be a priority.

 

But my point is you can still run at low flow temps in a relatively unimproved dwelling as long as you have reasonable radiators.

[ProDave]

2 hours ago, IGP said:

 And then HPs at <45c design flow temp as that is around at the point where SCOP for most HPs beats the spark gap and saves money for people (and be therefore can be seen as better, not just equal to gas).

Under the present gas / electricity pricing, a perfectly designed and set up HP install will only be marginally cheaper to run than a gas boiler, and a poorly installed one will cost more than a gas boiler.  As such the marginal saving (when done properly) is hardly a reason alone to invest money.  You have to do it for other reasons, not financial saving, and therein lies the problem with persuading millions of people with perfectly working gas heating why they should change for at best only a marginal reduction in running costs.

 

Building my new house, we had no mains gas available and I did not want a great big oil tank in the garden, so an ASHP was chosen as the only viable means of electric heating that brought running costs down to being comparable to mains gas.  I never expected it to be cheaper than mains gas would have been if available, and the fact it is cleaner than mains gas is just a bonus.

 

This has got me thinking. Perhaps trying to sell ASHP's as a replacement for gas boilers is targeting the wrong market?  Why not instead target people using electric resistance heating, like electric panel heaters, storage heaters, or even electric boilers?  Those users would see their heating use of electricity drop by about 1/3, saving them real money, not just marginal, and would reduce strain on the electricity grid which is already struggling at times.  Reduced electricity use would mean fossil fuel generation required less frequently.