Optimising hot water schedule

[NormanB]

I always subscribed to the idea the Hot Water Setpoint should be 60°C. Now that I have an air-source Heat Pump, the installer has recommended 53°C maximum. Anything higher will cost me ‘big time’. Surprisingly, 53°C now seems adequate. Admittedly, the mixer tap now needs to be ‘all the way round’ to the hot (that is, no added cold) but it’s got to be cheaper, no?

I’m beginning to think the old 60°C stemmed from when energy was dirt cheap the planet didn’t matter!

Just as an aside, if you’re wondering where I got the ° symbol from, on my iPhone I hover over the zero (0) and it pops up to the left as an option!

If you are actually using unmixed hot water at 53C you have unusually tough skin. My mixer thermostat is set for a maximum of 38C and we still mix down. Anything above 40 risks injury.

 

[NormanB]

Not sure what is wrong with my statement.

"If you are storing the water at 53C bacteria will grow.
If you are heating the water and then using it straight away no problem.
The length of time that the water is stored hot will determine how many bacteria will grow"

Your response to my carefully considered post was ‘Sounds like a faff to me.’

As a lifelong professional engineer I have no time for derisory comments that seek to undermine knowledge.

Our understanding of physics and thermodynamics continues to develop of course but nothing in the last 70 years has undermined the basic laws. Nothing I said contravened them.

In the days of cheap energy (which are likely never to return) we could generally afford to set DHW storage at 60 or even 65 and leave the system under thermostat control 365 days a year.

You could still do that if you are on benefits or have deep pockets but if you are in the ‘squeezed middle’ you will have unnecessarily large bills.

It may be a faff to understand how to match your DHW settings to your lifestyle but exercising the mind does have other benefits too.

 

[johna.clements]

We have a Legionella Routine programmed. The temperature is raised at 02:00 each Wednesday for 2 hours to 60°C. I appreciate your concern, but I think we’ve got that covered.

Not everybody has a program to heat the tank to 60C at 6pm Pacific Standard Time once a week to sanitize the system. Not sure why that time was choosen would think that 6pm GMT/BST would be more usefull as you could use that heat.

 

[johna.clements]

Your response to my carefully considered post was ‘Sounds like a faff to me.’

As a lifelong professional engineer I have no time for derisory comments that seek to undermine knowledge.

Our understanding of physics and thermodynamics continues to develop of course but nothing in the last 70 years has undermined the basic laws. Nothing I said contravened them.

In the days of cheap energy (which are likely never to return) we could generally afford to set DHW storage at 60 or even 65 and leave the system under thermostat control 365 days a year.

You could still do that if you are on benefits or have deep pockets but if you are in the ‘squeezed middle’ you will have unnecessarily large bills.

It may be a faff to understand how to match your DHW settings to your lifestyle but exercising the mind does have other benefits too.

I once again ask what is wrong with my statement.

"If you are storing the water at 53C bacteria will grow.
If you are heating the water and then using it straight away no problem.
The length of time that the water is stored hot will determine how many bacteria will grow"

As a professional engineer with a life time of experience do you think that bacteria does not grow in warm water?
Do you not think that time is a factor in the number of bacteria.

 

[Phil Pascoe]

If you are actually using unmixed hot water at 53C you have unusually tough skin. My mixer thermostat is set for a maximum of 38C and we still mix down. Anything above 40 risks injury.

I remember hot pools in NZ being 40° - 41°........... only the bravest of Asians went in them.

 

[johna.clements]

In the days of cheap energy (which are likely never to return) we could generally afford to set DHW storage at 60 or even 65 and leave the system under thermostat control 365 days a year.

You could still do that if you are on benefits or have deep pockets but if you are in the ‘squeezed middle’ you will have unnecessarily large bills.

I am not on benefits so do not know which benefit pays for all your heating bills. My understanding is that all the money is paid together apart from housing which is calculated separately. There is no direct funding of peoples normal gas bills, but if I am wrong please let me know.

 

[Spectric]

The whole system with all rads on is balanced correctly to start with.

For info radiators have a user operated valve on one end, might be a TRV and a lockshield valve on the other, this is the valve used to balance your rads.

 

[Glitch]

Your response to my carefully considered post was ‘Sounds like a faff to me.’

As a lifelong professional engineer I have no time for derisory comments that seek to undermine knowledge.

Our understanding of physics and thermodynamics continues to develop of course but nothing in the last 70 years has undermined the basic laws. Nothing I said contravened them.

In the days of cheap energy (which are likely never to return) we could generally afford to set DHW storage at 60 or even 65 and leave the system under thermostat control 365 days a year.

You could still do that if you are on benefits or have deep pockets but if you are in the ‘squeezed middle’ you will have unnecessarily large bills.

It may be a faff to understand how to match your DHW settings to your lifestyle but exercising the mind does have other benefits too.

For a professional engineer your attention to detail is lacking. You're having a pop at @johna.clements for a comment I made.

You said:
'Second in broad terms (all other things being equal) the hotter you drive your water temperature up the greater the rate of heat loss. You need to match your DHW schedule to your useage. We have a 210 litre DHW cylinder and raise the temperature every other day to 50 deg C, once a week to 60 (risk reduction legionella).'

Sounds like you are making manual adjustments every other day. I said that's a faff. That's not intended as a derisory comment, just an observation.
It's not undermining your knowledge, it's an opinion on the manual process you have created for yourself.
I've discovered my Nest system has a Bacteria Protection feature that does this automatically. It's a faff free solution to the Legionella risk.

I can only make a general assumption on how sensitive people might be and I know it's easy to misinterpret a comment. I do it regularly myself but usually double check and puts my hands up if I've read it wrong.

 

[NormanB]

For a professional engineer your attention to detail is lacking. You're having a pop at @johna.clements for a comment I made.

You said:
'Second in broad terms (all other things being equal) the hotter you drive your water temperature up the greater the rate of heat loss. You need to match your DHW schedule to your useage. We have a 210 litre DHW cylinder and raise the temperature every other day to 50 deg C, once a week to 60 (risk reduction legionella).'

Sounds like you are making manual adjustments every other day. I said that's a faff. That's not intended as a derisory comment, just an observation.
It's not undermining your knowledge, it's an opinion on the manual process you have created for yourself.
I've discovered my Nest system has a Bacteria Protection feature that does this automatically. It's a faff free solution to the Legionella risk.

I can only make a general assumption on how sensitive people might be and I know it's easy to misinterpret a comment. I do it regularly myself but usually double check and puts my hands up if I've read it wrong.

I am doing nothing manually, it’s all pre programmed including the once per week ‘hygiene cycle’ of a 60 degree programme.

Yes I made an error as my response was intended for you and not the ‘other guy’ - I have no excuse other than navigating multiple screens on a small phone.

 

[ivan]

We have a very large shoulder ht. cylinder, as on economy 7. The thermostat at the base of the cylinder has been set to 50 deg for the last 33 years. I guess it might get hotter at the top. We have been free of legonaires so far...

 

[NormanB]

I am doing nothing manually, it’s all pre programmed including the once per week ‘hygiene cycle’ of a 60 degree programme.

I once again ask what is wrong with my statement.

"If you are storing the water at 53C bacteria will grow.
If you are heating the water and then using it straight away no problem.
The length of time that the water is stored hot will determine how many bacteria will grow"

As a professional engineer with a life time of experience do you think that bacteria does not grow in warm water?
Do you not think that time is a factor in the number of bacteria.

First off apologies my comment was misdirected at you rather than the o/p.

Secondly, yes if you are storing hot water and not using it, then yes this can promote bacterial growth but you must then ask why are you using energy to store hot water without using it. A weekly hygiene cycle will ameliorate bacteriological growth and also minimise legionella risk in what is, anyway , a low risk domestic environment.

 

[Glitch]

For info radiators have a user operated valve on one end, might be a TRV and a lockshield valve on the other, this is the valve used to balance your rads.

Back to the challenge of optimising the Boiler/radiator performance.

I get the feeling that the condensing boiler would prefer the set up to be static with no variables to affect the performance.

A little knowledge is a dangerous thing but this is what I've gleaned from t'internet 'experts':
Traditionally you open up all the rad valves and find out the order in which they heat up.
Then the rads nearest the boiler and those in the upper stories (heat rises) have their lockshields restricted to a quarter turn open.
This is because the rads that heat up quicker need to reduce the flow through the rad to have min 12c difference between input and output flow to the rad.
Idea is to get some flow to the downstream rads to make sure they don't take ages to heat up and that heat is used to heat the rads and not just returned to the boiler.
Return temp should ideally be 20c less than boiler output temp.
There may be some nuances but I think that's the basic idea.

All work well if everything stays the same, including outside temp and humidity, indoor temperature (and humidity?), Radiator valves are not touched. HW heating doesn't kick in.
So it's better to keep all rads on. TRVs will disrupt the flow because they'll close the valve and push flow to downstream rads, and/or worse still, the boiler.
Turning off rads not needed will affect the balance, dependent on whether they are close to boiler or upstairs.

From my limited understanding it's a tricky problem to solve. There are too many variables that can affect the initial optimisation.
That's why someone came up with a smart pump and also other gadgets to help solve the problems.

https://www.bbc.co.uk/news/business-62900202

 

[NormanB]

I am not on benefits so do not know which benefit pays for all your heating bills. My understanding is that all the money is paid together apart from housing which is calculated separately. There is no direct funding of peoples normal gas bills, but if I am wrong please let me know.

Local Authorities have been allocated central funding for these purposes. Only those on benefits can access these local authority ‘hardship funds’.
https://www.gov.uk/government/publications/household-support-fund-guidance-for-local-councils

 

[Glitch]

I am doing nothing manually, it’s all pre programmed including the once per week ‘hygiene cycle’ of a 60 degree programme.

Yes I made an error as my response was intended for you and not the ‘other guy’ - I have no excuse other than navigating multiple screens on a small phone.

No problem.
You have an automated solution which is good.

Can you detect and boiler out and return flow temps, or is it just the water storage temperature that you can set?
I'm wondering if you have enough flexibility to tune the boiler in real time.

 

[johna.clements]

Local Authorities have been allocated central funding for these purposes. Only those on benefits can access these local authority ‘hardship funds’.
https://www.gov.uk/government/publications/household-support-fund-guidance-for-local-councils

That is discretionary spending, only some people will get it. If the fund runs out hard luck. You have to give a reason why you should get money from this hardship fund. If you needed additional electricity to run medical equipment you could get a grant if the money has not already been spent. If as you suggest you just want to walk around the house in your underwear when it is freezing outside with the windows open they will not give you a discretionary grant.

Your suggestion that people on benefits can use as much gas and electric as they want, and it will be paid by central government or local authorities, is nonsense.

 

[johna.clements]

All work well if everything stays the same, including outside temp and humidity, indoor temperature (and humidity?), Radiator valves are not touched. HW heating doesn't kick in.
So it's better to keep all rads on. TRVs will disrupt the flow because they'll close the valve and push flow to downstream rads, and/or worse still, the boiler.
Turning off rads not needed will affect the balance, dependent on whether they are close to boiler or upstairs.

From my limited understanding it's a tricky problem to solve. There are too many variables that can affect the initial optimisation.
That's why someone came up with a smart pump and also other gadgets to help solve the problems.

I think the question should be what is the cost/ benefit of running the system at different efficiencies. If you turn down the radiators in little used rooms will you be better off financially even though the boiler may then not be working as efficiently. If you save £100 a year to turn down the radiator in the box room, that has boxes in it, but the rest of the house costs £20 more to heat you gain £80.

I would assume that is how it works but I am a civil engineer not HVAC.

 

[dillon]

I always subscribed to the idea the Hot Water Setpoint should be 60°C. Now that I have an air-source Heat Pump, the installer has recommended 53°C maximum. Anything higher will cost me ‘big time’. Surprisingly, 53°C now seems adequate. Admittedly, the mixer tap now needs to be ‘all the way round’ to the hot (that is, no added cold) but it’s got to be cheaper, no?

I’m beginning to think the old 60°C stemmed from when energy was dirt cheap the planet didn’t matter!

Just as an aside, if you’re wondering where I got the ° symbol from, on my iPhone I hover over the zero (0) and it pops up to the left as an option!

My understanding, from an HSE inspector, is that 60 degrees is guaranteed to kill bacteria, particularly Legionella. If this is indeed the case you may want a word with your installer.

 

[Glitch]

I think the question should be what is the cost/ benefit of running the system at different efficiencies. If you turn down the radiators in little used rooms will you be better off financially even though the boiler may then not be working as efficiently. If you save £100 a year to turn down the radiator in the box room, that has boxes in it, but the rest of the house costs £20 more to heat you gain £80.

I would assume that is how it works but I am a civil engineer not HVAC.

I get what you're saying.

Apparently the maximum benefit you can get with a condensing boiler is 11% more efficiency than a non-condensing one.
My maximum saving, based on my latest London Power direct debit is £288 p.a.

Few will get anywhere near the full 11% benefit so let's assume I could get 5.5%.

So the target saving is around £144 p.a.

When the weather gets cold enough for me to turn the heating on I'll start tweaking.

 

[NormanB]

No problem.
You have an automated solution which is good.

Can you detect and boiler out and return flow temps, or is it just the water storage temperature that you can set?
I'm wondering if you have enough flexibility to tune the boiler in real time.

My boiler regulates itself to achieve a Delta T of 20C across the boiler heat exchanger, DHW cylinder temperature is on its own stat. On heating duty I have zero room room thermostats and control is effected using weather compensation and during commissioning the slope and origin of the control curve was set up to match the heat loss of the house. It is an iterative process (at different ambients) and no heating engineer working for a customer would spend the time required to optimise it as I have. But once set up that’s it and it will use the minimum of energy to keep the house at ‘set point’ monitoring outside ambient to ensure minimum burn (boiler modulates down to 1.9KW) ensuring maximum condensing at the hex.

It is a Viessman 200W fitted with priority DHW on a 4 pipe system. I also fitted IMI constant flow valves on all radiators (these are set to match flow rate to emitter capacity ) so no need for guesstimate balancing on low authority lockshield valves (which are honestly not really up to that task). Standard (non smart) TRVs fitted on every emitter (radiator).

I also range rated my boiler to 6KW to match the heat loss of my house (did my own heat loss calcs).

In my opinion the Viessman 200 has the best boiler controls and modulation in the current market.

 

[1steven]

Viessman are great boilers