Heating thermostat in the hallway

[NormanB]

There is simply no magic one size fits all for this conversation.

First things first if you want to cut heating bills then you need to understand how your house loses heat and how much ( a proper heat loss calculation will tell you)
You also need to understand how you use and interact with your house. (This is information any heating engineer should be skilfully extracting from their clients)
You also need to take on some interesting physics along the lines of it takes more energy to heat a litre of water from 5 to 50 degrees C than it does to maintain it at 35 degrees C and then top it up to 50 degrees when needed. (Obvious caveats here - how long are we storing it at 35 and how quickly does the environment its stored in allow the heat to escape.)

Its the first and last of these three things which can be manipulated to increase the overall efficiency of a heating system.

In terms of heat loss we can insulate better and this is a massive help, but if you live in a Victorian town house with single glazed sash windows then just accept your gonna need more gas!

Interaction is a complex one, if people are allowing certain areas of a house to become cold (spare rooms etc) then this can affect the heat loss calculation as generally any heat loss calculation would assume a spare room connected to say a bedroom, that spare room would be at 16 degrees C or even 18 degrees C. Therefore if your spare room is down at 5 or 6 degrees or lower then thats the equivalent of turning your poorly insulated internal bedroom wall into an externally facing wall.

As can be seen from the point above physics controls how quickly a space looses heat and consequently how much heat must be put into a space to maintain or heat it. if we have an internal space surrounded by other internal heated spaces (all sides and above and below) then the heat required will be alot less than if that same space is surrounded by the unheated cold outdoors (think shed or unheated garage in winter)


Historically heating boilers were either on or off and they output heat at a pretty fixed temperature depending on what position the rotary knob was set at on the front. The boilers themselves were massively inefficient usually due to the incorrect ratio of air and gas being burned.
In laymen's terms, if you put a £100 of gas into an old non condensing boiler you would achieve roughly £45 to £55 of useful heat into your house whereas when running efficiently that same £100 of gas put into a modern condensing boiler will achieve roughly £83 to £95 of useful heat into your house.

Modern boilers and controls allow further efficiency by modulating the heating water flow temperature around your house depending on the external temperature. Remember our heat loss calculation - with this we understand how much heat in KW or Btu's our house needs to maintain or increase temperature for a given set of environmental variables (outside temperature and the known rate at which our house looses heat)
Using our modern controls we can increase or decrease the boiler flow temperature, when its say 14 degrees externally we only need a low heat to be circulated around our system to maintain or increase the internal temperature as the heat loss from our house is relatively slow and small. However when its -3 outside modern controls will automatically increase the boiler heating flow temperature to maintain or increase our house temperature.


When installed properly and set up/used correctly modern smart controls will run a heating system to an optimum, however they can only do this if all the above factors have been taken into account and they cannot predict the chances of some glorious winter sun streaming through the windows providing a reasonable solar uplift to internal temps an hour after said controls have heated the space!

I fully understand why some people prefer to tinker and constantly turn up / down the heating (usually the older generation cos thats what we did) but in a well understood house with modern controls the heating can be left to its own devices and provide a comfortable user defined temperature 365 days a year with likely over the long term the most efficient use of gas.
If one day a 'tinkerer' turns up to high a radiator to heat a usually unused space and accidently leaves it on high or opens a window and forgets the heating is on then any perceived savings are gone.


The full evolution of smart controls will see individual radiator thermostatic heads (TRV heads) replaced with smart thermostatic heads which will provide even more control and effectively change single zone heating systems into multizone heating systems where individual room temps can be monitored and heat maintained or lifted as needed to run a heating system in the most efficient way possible.


Well that's enough rambling from me, and of course these are musings from my understanding and opinions so any professors out there who wish to dismiss my musings please do so

Bravo - excellent post.

 

[NormanB]

In trying to cut our heating bills via research on the internet, it seems to me that there is a certain amount of low hanging fruit which is obvious but that most of it comes down to individual situation. There are a massive number of variables in every property and what works well in one might do the opposite in another.

Through choice, we live in a reasonably large hybrid house in the country. Heating is by oil (no mains gas), hydroponic underfloor in all but two rooms - those being wood burners. I don't see GSHP or ASHP as the answer for now because everything suggests we need a massive improvement in insulation (which will upset the fabric of the house too much) and the insulation and uPVC glazing, in the main, isn't too bad. Anyway, one installer suggested that we would need a second single phase power supply or a conversion to three phase so as to power the heat pumps. That, in itself, rang alarm bells for me.

So, we're running incremental experiments for our use case. I've changed five of the eleven thermostats from mechanical dial to programmable and we're going to try temperature set back at night. At the same time, the other six thermostats are being set to a relatively low temperature and the doors to those rooms shut. There's no sense in heating a bedroom containing a turbo trainer, for example. This flies in the face of some of the stuff that I have read on the web but, we will give it a go.

Between the middle of November and the first week of December, with temperatures cooling but not cold, we were burning about £13.50 of oil per day. In the past week, with these changes and with my sister-in-law visiting (so her bedroom heated) and it being around freezing day and night outside, the heating cost has been about the same as back in November. Measuring oil usage is difficult as there is no meter. Instead, it's a dipstick, a retractable ruler and an Excel calculation. It's too soon to tell if these changes have made a difference or not - five days of cold weather and the daily cost is no worse than before. It seems to me that, with heating costs as they are, a few hundred quid on thermostats is worth the investment as a trial.

For me, the technology isn't mature enough to convince me to invest a massive amount of money in something which is a bit of a punt (GSHP, ASHP, being examples) and the motives behind some of what is being peddled appear questionable - Boris promoting heat pumps, for me, being a prime example.

Heat pump technology is mature and well proven. What is not mature and well proven is the industry to match the system design in the house to accommodate a heat pump. Like all government initiatives as soon as taxpayer cash is there for the picking it attracts the cowboys and chancers. So poor design, incorrect equipment selection, errors on control sensors and commissions have resulted in heartbreaking stories and phoenix companies who go into liquidation to avoid litigation/liabilities and then reappear under a different name.

The trick is to identify a competent and proven designer/installer.

By the way hydroponics is growing plants/crops using water and nutrients without soil. An unusual benefit of you current heating system.

 

[dgs2001]

What are you basing that assertion on? If that were true for a couple of hours at 35 degrees, why not for a year?
I'd be interested to see a link to this interesting physics.

Perhaps I did not explain that bit very clearly.

The energy required to heat water is, i think is as follows -
The specific heat of water is 4182 J/(kg*°C).
That means that it takes 4182 Joules to heat 1 kg of water by 1°C.
So to heat our litre of cold water from 10 Degrees to 50 Degrees we are looking at a sensible heat requirement of 167.3 Kilojoules (KJ)

Ok, Monday morning we purchase enough gas to heat our 1 litre (1KG) of water from 10 degrees to 50 degrees (167.3KJ of gas)
I haven't worked out how much gas this needs but lets just say for arguments sake its exactly £5 worth.

Monday afternoon we go to work and from work we go to the pub, get lucky and we return home from a 2 day extravaganza on Wednesday afternoon.
Wednesday afternoon through the brain fog we discover our 1KG of water is now cold again, strangely 10 degrees.

Ok, Wednesday afternoon we purchase enough gas to heat our 1 litre (1KG) of water from 10 degrees to 50 degrees (167.3KJ of gas)
I haven't worked out how much gas this needs but lets just say for arguments sake its exactly £5 worth.
(You can see where this is going - its cost us £10 to heat the same 1kg of water twice)

Wednesday evening we are at home feeling sorry for our hungover party existence and curl up with the heating on, yes we are buying more gas to run the heating but its for the heating and entirely separate to our 1kg of hot water.
A by product of having the heating on is that the environment our 1kg of water is stored in is now at 21 degrees not 10 degrees and so our water cools to 21 degrees not 10 degrees.

Thursday morning we purchase enough gas to heat our 1 litre (1KG) of water from 21 degrees to 50 degrees (121.28KJ of gas)
And hey presto its only cost us £3 to top up the hot water not £5.

Ok not so much physics but I believe modelled by complex software around real life rather than lab conditions, and by people way above my pay grade.

The point I was making is understanding the way people are using their homes is part of the puzzle of reducing costs, however I do believe that smart controls can be an asset to that end.

 

[ian33a]

Hi Norman,

Your point about heat pumps is valid - they have been around for ages - and I agree that the world and his dog are trying to capitalise on the opportunity, and this is where the problems come.

Hydroponics, yes, guilty as charged. "Hydronics", is probably a better description.

Out of interest, as an engineer (but from electronics, not heating), can you recommend any websites or tools where I can begin to build a heat loss calculation for my hybrid house? It will help me understand what is happening better, well hopefully anyway.

 

[Spectric]

The quality of the training is recognised and attracted government investment too.

Sounds like it is a shame that the government is not listening and still pushing the wrong systems forward.

 

[Spectric]

The solution is called weather compensation control.
The outside temperature is monitored, and as it gets colder it 'turns up the boiler stat' increasing the boiler flow temperature.

Yes and no, if the house had zero heat loss then outside temperature would be irrelevant but as we all know we are all contributing to heating up the outside atmosphere through heat loss. But outside temperature is an important parameter that could be used by a control system to manage our heating but not by increasing the flow temperature beyond the point at which it stops condensing, so instead modulate the gas burners so they provide less input when they are just maintaining a temperature and more when they are increasing the temperature which would give fast warm up and you could have a self learning algorithm that would learn your control system and adjust to suit your property.

 

[Geoff_S]

You would think that there is a major opportunity here for the people that know so much, to set up a professional individual assessment and advice service for the domestic punter so that we can get a definitive answer as to what to do.

I would pay money for that.

 

[Pedronicus]

You would think that there is a major opportunity here for the people that know so much, to set up a professional individual assessment and advice service for the domestic punter so that we can get a definitive answer as to what to do.

I would pay money for that.

Not any easy thing to do when one considers that most domestic punters look at one thing and one thing only - the price. Most would be unwilling to pay for something that they feel they can learn from the internet for free.

There are also so many variables with each installation that a site visit would be necessary which would need to be paid for. Then there is the issue of liability if the system doesn't work 'as expected' (an useful get-out for the punter) and they end up telling porkies about how they used the system.

A good idea on paper but not in reality I fancy.

 

[NormanB]

Sounds like it is a shame that the government is not listening and still pushing the wrong systems forward.

What ‘wrong systems’ are being pushed forward?

 

[John Brown]

Yes and no, if the house had zero heat loss then outside temperature would be irrelevant but as we all know we are all contributing to heating up the outside atmosphere through heat loss. But outside temperature is an important parameter that could be used by a control system to manage our heating but not by increasing the flow temperature beyond the point at which it stops condensing, so instead modulate the gas burners so they provide less input when they are just maintaining a temperature and more when they are increasing the temperature which would give fast warm up and you could have a self learning algorithm that would learn your control system and adjust to suit your property.

If the house had zero heat loss, it wouldn't need any central heating.

 

[Pedronicus]

If the house had zero heat loss, it wouldn't need any central heating.

Really? Care to expand on that little gem?

 

[John Brown]

Really? Humans produce somewhere between 100 and 100 watts of heat, so with zero heat loss....
Unless you're dead, but even then, with zero heat loss the exothermic reactions as your body rots would warm a dwelling with zero heat loss.

 

[NormanB]

Hi Norman,

Your point about heat pumps is valid - they have been around for ages - and I agree that the world and his dog are trying to capitalise on the opportunity, and this is where the problems come.

Hydroponics, yes, guilty as charged. "Hydronics", is probably a better description.

Out of interest, as an engineer (but from electronics, not heating), can you recommend any websites or tools where I can begin to build a heat loss calculation for my hybrid house? It will help me understand what is happening better, well hopefully anyway.

The best ‘tools’ are subscription. I used a free web based tool (which I found from Google) which is probably not as good because it is free. Free web based tool.

Overall I figure it overestimated my overall heat loss by quite a margin which is a massive limitation ( actually a disaster) if you were considering heat loss in order to select a heat pump (not so critical with a gas’s boiler) but room by room it’s probably ‘good enough’ for sizing emitters.

When all said and done these tools (even the best ones) are theoretical and make assumptions. You may, for example, adequately describe construction and insulation etc - but you cannot describe cold bridging and other quality departures from design intent.

However, as the homeowner, you have the time and resource that you would not want to pay a professional for and that is calculating your actual heat loss. Buy a dozen room thermometers (I purchased bluetooth ones) and set your heating up to achieve a steady 21C - check the outcome, adjusting as necessary. Now the tricky part - track the energy consumed to achieve that at a given ambient temp - per day. Now is a good time to do it, at -2C is even better (the reference temp) for heat loss calcs.

For me that is relatively easy (gas boiler) as I know the energy input of the boiler (and broad efficiency) so know the energy transfer into the dwelling. I do it per 24hr period and a simple average of actual daily ambient.

For me yesterday with an average ambient of -0.3C and stable 21 throughout the 24 hour period the heat energy transfer into the dwelling was around 4.7KW.hr/hr. So that must also be the average hourly heat loss. My free tool was suggesting 12Kw.hr/hr! (At -2C) - Of course you actually need peak heat loss at -2C so my averaging is a bit crude but probably closer than theoretical modelling, I certainly do not believe I will use 4.7 KW.hr/hrx 3 for the next -1.7C.

 

[NormanB]

Yes and no, if the house had zero heat loss then outside temperature would be irrelevant but as we all know we are all contributing to heating up the outside atmosphere through heat loss. But outside temperature is an important parameter that could be used by a control system to manage our heating but not by increasing the flow temperature beyond the point at which it stops condensing, so instead modulate the gas burners so they provide less input when they are just maintaining a temperature and more when they are increasing the temperature which would give fast warm up and you could have a self learning algorithm that would learn your control system and adjust to suit your property.

I am not at all convinced you understand how a properly implemented weather compensation system actually works with a gas boiler.

 

[jimbowley]

Well that's enough rambling from me, and of course these are musings from my understanding and opinions so any professors out there who wish to dismiss my musings please do so

You allowed for comments so here they are I'm not a professor but a mechanical engineer who got A's in thermodynamics.


1). Letting the temperature fall lower and then reheating [A] will use less energy than maintaining at an intermediate temp and then re-heating .

To model this for sizing say a boiler would need delta temperatures and heat capacities and heat conductance values, not too hard (but hard in text format) and also not general. But there's an easier way to think about it, which is to only look at the heat loss which is proportional to delta temperature. At every time point the indoors/object temp is lower or equal in scenario A so the total heat loss is less. The start and end points of each scenario are all the same Temp so there are no stored energy deltas to complicate issues.

In [A] it will take longer to heat the house from the decision point to turn the heat up, but that will only save additional energy by being less responsive.


2). Turning off the heat in a bedroom and closing the door will save energy.

Again we only need to look only at the external heat loss. The inside temp of the bedroom external walls and windows will be lower than when the room was heated, therefore less energy will be flowing out through those walls.

Note: You haven't replaced an external wall by an internal wall; You have added an internal wall and 12 foot air gap to the same external wall.

 

[Spectric]

If the house had zero heat loss, it wouldn't need any central heating.

If it had no central heating then there would be no heat to lose, but with full insulation you only need minimal heat input to keep it warm so not a boiler based system and massive savings, so why are we still not building the right properties needed for the future.

 

[John Brown]

If it had no central heating then there would be no heat to lose, but with full insulation you only need minimal heat input to keep it warm so not a boiler based system and massive savings, so why are we still not building the right properties needed for the future.

Because the housebuilding firms have the ear of the government. Proper insulation should have been mandatory on new builds for decades.

 

[Pedronicus]

Again we only need to look only at the external heat loss. The inside temp of the bedroom external walls and windows will be lower than when the room was heated, therefore less energy will be flowing out through those walls.

Can I ask your thoughts on the fact that any surrounding connected rooms adjacent to the bedroom will loose heat quicker by transfer through the internal walls/ceilings owing to the increased ▲t thereby causing the temperature in said rooms to drop accordingly. This temperature drop will require additional heat into the connected rooms to return them to the previous state before switching off the bedroom radiator.

Bear in mind we are talking about every day properties not super insulated ones.

 

[jimbowley]

Can I ask your thoughts on the fact that any surrounding connected rooms adjacent to the bedroom will loose heat quicker by transfer through the internal walls/ceilings owing to the increased ▲t thereby causing the temperature in said rooms to drop accordingly. This temperature drop will require additional heat into the connected rooms to return them to the previous state before switching off the bedroom radiator.

Bear in mind we are talking about every day properties not super insulated ones.

Let's see....

Yes, adjacent rooms will lose heat into the cold room. Therefore they will either be slightly colder than before {A} or they will draw more energy from their heat source to maintain their temp {B}.

In {A} another room will be cooler than before, therefore less heat loss to external = even more savings.

In {B} I need to show that the extra heat output from the remaining heaters is less than was coming out of the turned off heater. ie that the total heating energy is less. To show that with the details (individual temperatures and radiator outputs) requires running the 2 detailed models against each other. But again I can simplify by choosing my system boundary as the external walls, and we are back to: if every external wall is at the same or lower temperature then the heat loss will be less.


edit: There doesn't need to be a heater to turn off, closing the door on an unheated bedroom will also lower the delta temperature across some external walls which will reduce heat flow to outside.

 

[Misterdog]

My quite old condensing boiler has that feature, but it's manual, sadly. I suppose I could automate it with a stepper motor to turn the control...

A simple external sensor was less than £20 when I fitted mine, 2 wires so even a chippy can fit it.

Most are now linked to weather forecasts and wi-fi.