how hot do you run you CH boiler
I had a new Combi fitted today (in the to-be-moved-to house).
Fitters told me that I should run this at 74 degrees. Which I thought far too high, as 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" and the completely bogus "the temperature of the water in the radiators is set by the TRVs not the boiler temp. I couldn't persuade the guy that he was taking bollox, he played the "I'm the experience heating engineer card and I know better than you" card. **** Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do tim |
how hot do you run you CH boiler
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" and the completely bogus "the temperature of the water in the radiators is set by the TRVs not the boiler temp.Â* I couldn't persuade the guy that he was taking bollox, he played the "I'm the experience heating engineer card and I know better than you" card.Â* **** Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do tim Electric boiler so not concerned with condenser temperature bollox, always 100% efficient .. Run ours at 80C normally, if really cold ramp it up to 85C on the basis of highest coupling efficiency between rads and air. Fastest heatup. No kids so rad temp not an issue. |
how hot do you run you CH boiler
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as Indeed... 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period It might be required in particularly cold weather, but most of the time you will be able to use less. I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" You will most heat recovered from the condenser when the return temperature is below about 54 degrees (the dew point of the flue gasses). and the completely bogus "the temperature of the water in the radiators is set by the TRVs not the boiler temp.Â* I couldn't persuade the guy that he was taking bollox, he played the "I'm the experience heating engineer card and I know better than you" card.Â* **** Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do I have weather compensation on mine, and so it chooses its own temperature based on the outside temp. Basically that means its runs as cool as it thinks it can get away with and still be able to reach the target set point temperature in a reasonable amount of time. (the relationship is set by choosing a mapping curve that reflects the rate of heat loss of the building). Currently the external temp is 6.5 deg C, and the flow temp is running at 54 deg. If it were to go well below 0, then it might push the flow temp up into the 70s. When its milder it might run flow temps down in the 40s. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
how hot do you run you CH boiler
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as Indeed... 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period It might be required in particularly cold weather, but most of the time you will be able to use less. I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" You will most heat recovered from the condenser when the return temperature is below about 54 degrees (the dew point of the flue gasses). and the completely bogus "the temperature of the water in the radiators is set by the TRVs not the boiler temp.Â* I couldn't persuade the guy that he was taking bollox, he played the "I'm the experience heating engineer card and I know better than you" card.Â* **** Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do I have weather compensation on mine, and so it chooses its own temperature based on the outside temp. Basically that means its runs as cool as it thinks it can get away with and still be able to reach the target set point temperature in a reasonable amount of time. (the relationship is set by choosing a mapping curve that reflects the rate of heat loss of the building). Currently the external temp is 6.5 deg C, and the flow temp is running at 54 deg. If it were to go well below 0, then it might push the flow temp up into the 70s. When its milder it might run flow temps down in the 40s. I thought the advice was to heat DHW to 60 degrees to avoid the risk of legionella, and that's not going to happen if the boiler's running at a lower temp. |
how hot do you run you CH boiler
wrote:
I thought the advice was to heat DHW to 60 degrees to avoid the risk of legionella, and that's not going to happen if the boiler's running at a lower temp. That may be true, but in practice I dont think Legionella has ever proved to be a problem in domestic systems. Tim -- Please don't feed the trolls |
how hot do you run you CH boiler
On Friday, 11 January 2019 18:54:03 UTC, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" and the completely bogus "the temperature of the water in the radiators is set by the TRVs not the boiler temp. I couldn't persuade the guy that he was taking bollox, he played the "I'm the experience heating engineer card and I know better than you" card. **** Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do tim The only realistic answer is to run it as hot as is necessary to provide enough heating. Cooler means more boiler efficiency, hotter means more rad output. The required target temp varies from one house & install to another, and varies with the weather. NT |
how hot do you run you CH boiler
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" The instruction manual for my Ideal says that the 'e' setting is best for condensing, which is quite hot. I don't understand this as I would have thought that the cooler the returning water temperature the more condensing. I use a much lower temperature as I don't have a room thermostat and the TRVs are fiddly and don't seem to keep the air temperature constant. -- Max Demian |
how hot do you run you CH boiler
tim... pretended :
I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as I have an opened vented system, with stored HW and the house is heated by the one boiler, installed new last March. A Vailant ECOfit Pure 418. We like the stored water to be good and hot, the boiler only has one temperature setting available for its output temperature - so I have it set at its max, of 75C, in order to meet our HW needs. The house heating would be satisfied by a lower boiler temperature around 60C and it would be more gas efficient, but unless I manually manage the temperature setting I am stuck with the less efficient 75C. I even tried to find a way to fool the boiler into working at a lower output temperature, by adding a separate bi-metal stat on the boiler output pipe to CH only, set at 60C, to shut it down at that temperature - as heating satisfied. That was a miserable failure, in that the boiler constantly cycled on/off via the stat, whilst ever the room stat indicated a demand, rather than modulating its output down - as it would on its own as it neared its 75C setting. If anyone knows a workaround, to allow split boiler output temperatures on this boiler - do let me know please. |
how hot do you run you CH boiler
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. snip Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do I have weather compensation on mine, and so it chooses its own temperature based on the outside temp. Basically that means its runs as cool as it thinks it can get away with and still be able to reach the target set point temperature in a reasonable amount of time. (the relationship is set by choosing a mapping curve that reflects the rate of heat loss of the building). I don't follow how that can work properly, as for most homes different rooms will have a different 'curve'. Or does tweaking the TRV compensate? -- Cheers, Rob |
how hot do you run you CH boiler
On 11/01/2019 23:33, Max Demian wrote:
On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" The instruction manual for my Ideal says that the 'e' setting is best for condensing, which is quite hot. I don't understand this as I would have thought that the cooler the returning water temperature the more condensing. My understanding of the 'e' mark on my Ideal boiler's central heating temperature control is that any setting above is non-condensing. Any setting below and the boiler's condensing. I use a much lower temperature as I don't have a room thermostat and the TRVs are fiddly and don't seem to keep the air temperature constant. -- Cheers, Rob |
how hot do you run you CH boiler
On Friday, 11 January 2019 22:35:12 UTC, Tim+ wrote:
wrote: I thought the advice was to heat DHW to 60 degrees to avoid the risk of legionella, and that's not going to happen if the boiler's running at a lower temp. That may be true, but in practice I dont think Legionella has ever proved to be a problem in domestic systems. Oh yes it has. Plenty of people have died. https://www.dailymail.co.uk/news/art...ish-homes.html |
how hot do you run you CH boiler
On Friday, 11 January 2019 23:33:44 UTC, Max Demian wrote:
On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" The instruction manual for my Ideal says that the 'e' setting is best for condensing, which is quite hot. I don't understand this as I would have thought that the cooler the returning water temperature the more condensing. I use a much lower temperature as I don't have a room thermostat and the TRVs are fiddly and don't seem to keep the air temperature constant. -- Max Demian TRVs don't work. They are more influenced by the nearby radiator temperature than the room air temp. You can get them with remote sensors. They work. |
how hot do you run you CH boiler
On 12/01/2019 00:55, RJH wrote:
On 11/01/2019 21:30, John Rumm wrote: On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. snip Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do I have weather compensation on mine, and so it chooses its own temperature based on the outside temp. Basically that means its runs as cool as it thinks it can get away with and still be able to reach the target set point temperature in a reasonable amount of time. (the relationship is set by choosing a mapping curve that reflects the rate of heat loss of the building). I don't follow how that can work properly, as for most homes different rooms will have a different 'curve'. Or does tweaking the TRV compensate? It seems to work well enough in practice. Each room also has a TRV, and I have the place split into two zones; upstairs and downstairs, so that will account for some variation. It needs a little bit of experimentation to set the profile the first time - basically waiting for colder days and seeing if the system still heats the place comfortably and quickly enough. If it doesn't, then you just tweak it up to a steeper curve. It also helps if you have appropriate rad sizes for the rooms, and the system is balanced. The response curves look like: http://wiki.diyfaq.org.uk/index.php/...tingCurve1.png IIRC the system defaults to the 1.2 line. If you live in a super insulted place / particularly sheltered location then you would tweak down. In my case (exposed location - solid wall construction), I needed to go up. I found the 1.8 curve worked well. The system is also smart enough to automatically shift the response curve vertically based on the currently demanded internal target temperature[1]: http://wiki.diyfaq.org.uk/index.php/...tingCurve2.png So if you tweak the room temp up or down during the day (or have different times programmed with different set point temps), then it can vary the flow temperature to match the requirement. [1] Note that all the system temperatures sensors (internal downstairs, internal upstairs, DHW cylinder, and external) are digitized and processed as actual temperatures, not just as on/off "call for heat" style demands. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
how hot do you run you CH boiler
On 11/01/2019 22:42, wrote:
On Friday, 11 January 2019 18:54:03 UTC, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" and the completely bogus "the temperature of the water in the radiators is set by the TRVs not the boiler temp. I couldn't persuade the guy that he was taking bollox, he played the "I'm the experience heating engineer card and I know better than you" card. **** Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do tim The only realistic answer is to run it as hot as is necessary to provide enough heating. Cooler means more boiler efficiency, hotter means more rad output. The required target temp varies from one house & install to another, and varies with the weather. yup, spot on. It leaves three options: set and forget - chose a high flow temp that meets the worst case, and accept that you will be running with less efficiency / comfort for most of the year. manual - adjust the flow temperature yourself in response to particularly cold days - probably works quite well for users who are clued up enough to understand the requirement. automatic - use weather compensation to "close the loop". -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
how hot do you run you CH boiler
On 11/01/2019 23:33, Max Demian wrote:
On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" The instruction manual for my Ideal says that the 'e' setting is best for condensing, which is quite hot. I don't understand this as I would have thought that the cooler the returning water temperature the more condensing. I use a much lower temperature as I don't have a room thermostat and the TRVs are fiddly and don't seem to keep the air temperature constant. If your boiler allows external timers consider getting a TADO or Drayton Wiser (Or just wireless TRVs and a Reaspberry PI if you are the adventurous type). Lets you see what temp the TRVs think the room is at. Dave |
how hot do you run you CH boiler
On 11/01/2019 23:48, Harry Bloomfield wrote:
tim... pretended : I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as I have an opened vented system, with stored HW and the house is heated by the one boiler, installed new last March. A Vailant ECOfit Pure 418. We like the stored water to be good and hot, the boiler only has one temperature setting available for its output temperature - so I have it set at its max, of 75C, in order to meet our HW needs. The house heating would be satisfied by a lower boiler temperature around 60C and it would be more gas efficient, but unless I manually manage the temperature setting I am stuck with the less efficient 75C. I even tried to find a way to fool the boiler into working at a lower output temperature, by adding a separate bi-metal stat on the boiler output pipe to CH only, set at 60C, to shut it down at that temperature - as heating satisfied. That was a miserable failure, in that the boiler constantly cycled on/off via the stat, whilst ever the room stat indicated a demand, rather than modulating its output down - as it would on its own as it neared its 75C setting. If anyone knows a workaround, to allow split boiler output temperatures on this boiler - do let me know please. IME many of the Vaillant boilers do support split temperature operation, but it does depends on what controls you have them paired with. The 400 series Vaillant I did (probably previous model range, since this was = 12 years ago), actually had separate knobs on the front for CH and DHW flow temperatures. Although that was retrofitted into system with traditional controls that could not distinguish between the source of the call for heat - hence the DHW control never came into play and it ran like your system does. The blurb on their web site: https://www.vaillant.co.uk/for-insta...ler-26116.html Seems to suggest its compatible with the VRC 700 weather compensating controls, so that ought to allow split temperature as well. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
how hot do you run you CH boiler
Max Demian explained :
I use a much lower temperature as I don't have a room thermostat and the TRVs are fiddly and don't seem to keep the air temperature constant. That is at odds with my own findings, since installing TRV's last March, but I do have a room stat, in the hall and no TRV on just that one rad. I tried setting the TRV's up in March for each room, but there wasn't much need for heat at all then. I found it better to set them once the cold weather arrived this winter. Having gradually tweaked each to a comfortable temperature, they work pretty well. Working on just a room stat, the temperature variation was quite noticeable as the boiler kicked in and out on just the room stat.. |
how hot do you run you CH boiler
John Rumm pretended :
It needs a little bit of experimentation to set the profile the first time - basically waiting for colder days and seeing if the system still heats the place comfortably and quickly enough. If it doesn't, then you just tweak it up to a steeper curve. It also helps if you have appropriate rad sizes for the rooms, and the system is balanced. Balanced? I have always assumed there was no need to balance a system, where TRV's are installed. |
how hot do you run you CH boiler
It happens that John Rumm formulated :
set and forget - chose a high flow temp that meets the worst case, and accept that you will be running with less efficiency / comfort for most of the year. Which is what I have done. The TRV's prevent the rads getting hotter than needed for each room, except when the heating is first put on with the house 'cold'. In quotes, because it never gets truly cold. To mitigate turning the heating on from cold and the room temperature over shooting, I tend to nudge the room stat up in a series of steps over several minutes. |
how hot do you run you CH boiler
wrote in message ... On 11/01/2019 21:30, John Rumm wrote: On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as Indeed... 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period It might be required in particularly cold weather, but most of the time you will be able to use less. I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" You will most heat recovered from the condenser when the return temperature is below about 54 degrees (the dew point of the flue gasses). and the completely bogus "the temperature of the water in the radiators is set by the TRVs not the boiler temp. I couldn't persuade the guy that he was taking bollox, he played the "I'm the experience heating engineer card and I know better than you" card. **** Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do I have weather compensation on mine, and so it chooses its own temperature based on the outside temp. Basically that means its runs as cool as it thinks it can get away with and still be able to reach the target set point temperature in a reasonable amount of time. (the relationship is set by choosing a mapping curve that reflects the rate of heat loss of the building). Currently the external temp is 6.5 deg C, and the flow temp is running at 54 deg. If it were to go well below 0, then it might push the flow temp up into the 70s. When its milder it might run flow temps down in the 40s. I thought the advice was to heat DHW to 60 degrees to avoid the risk of legionella, and that's not going to happen if the boiler's running at a lower temp. the temp for the hot water and CH system are set independently in a combi |
how hot do you run you CH boiler
wrote in message ... On Friday, 11 January 2019 18:54:03 UTC, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" and the completely bogus "the temperature of the water in the radiators is set by the TRVs not the boiler temp. I couldn't persuade the guy that he was taking bollox, he played the "I'm the experience heating engineer card and I know better than you" card. **** Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do tim The only realistic answer is to run it as hot as is necessary to provide enough heating. Cooler means more boiler efficiency, hotter means more rad output. The required target temp varies from one house & install to another, and varies with the weather. The house, um flat, is well insulated I have been living in it part time for the past 6 weeks with no heating at all. It was a bit on the cold side but not unbearable Now that the heating is working, it will need to provide a very small amount of heat to keep the place warm I am more interested in the effect on the reliability of the boiler of setting a low temp, as there is no possibility that such a setting wont warm the house. tim |
how hot do you run you CH boiler
"Harry Bloomfield" wrote in message ... tim... pretended : I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as I have an opened vented system, with stored HW and the house is heated by the one boiler, installed new last March. A Vailant ECOfit Pure 418. We like the stored water to be good and hot, the boiler only has one temperature setting available for its output temperature - so I have it set at its max, of 75C, in order to meet our HW needs. not something that is a consideration with a combi |
how hot do you run you CH boiler
After serious thinking harry wrote :
TRVs don't work. They are more influenced by the nearby radiator temperature than the room air temp. You can get them with remote sensors. They work. They work absolutely fine here, once the heating has been on for a while and the system has settled down. I am able to log/graph room temperatures and once temperature is achieved, I only see variations of around 0.5C in the graphs. What TRV's or any type of stat cannot cope with is the overshoot, when the heating is suddenly turned on, or the stat suddenly turned up to a much higher setting. |
how hot do you run you CH boiler
"Harry Bloomfield" wrote in message ... John Rumm pretended : It needs a little bit of experimentation to set the profile the first time - basically waiting for colder days and seeing if the system still heats the place comfortably and quickly enough. If it doesn't, then you just tweak it up to a steeper curve. It also helps if you have appropriate rad sizes for the rooms, and the system is balanced. Balanced? I have always assumed there was no need to balance a system, where TRV's are installed. if TRVs can be set to reliably keep a room at, say 20 degrees, then it doesn't but if they can't, then it does I'm about to find out if the first line is true, because it is clear than my new systems is not balanced. As it is currently set, the lounge is like a sauna, and the rest of the house still cool. I actually don't have a problem with the latter, it's the former that's the issue tim |
how hot do you run you CH boiler
On 12/01/2019 08:56, tim... wrote:
wrote in message ... On 11/01/2019 21:30, John Rumm wrote: On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as Indeed... 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period It might be required in particularly cold weather, but most of the time you will be able to use less. I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" You will most heat recovered from the condenser when the return temperature is below about 54 degrees (the dew point of the flue gasses). and the completely bogus "the temperature of the water in the radiators is set by the TRVs not the boiler temp.Â* I couldn't persuade the guy that he was taking bollox, he played the "I'm the experience heating engineer card and I know better than you" card. **** Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do I have weather compensation on mine, and so it chooses its own temperature based on the outside temp. Basically that means its runs as cool as it thinks it can get away with and still be able to reach the target set point temperature in a reasonable amount of time. (the relationship is set by choosing a mapping curve that reflects the rate of heat loss of the building). Currently the external temp is 6.5 deg C, and the flow temp is running at 54 deg. If it were to go well below 0, then it might push the flow temp up into the 70s. When its milder it might run flow temps down in the 40s. I thought the advice was to heat DHW to 60 degrees to avoid the risk of legionella, and that's not going to happen if the boiler's running at a lower temp. the temp for the hot water and CH system are set independently in a combi I was replying to John (but had forgotten about combis) |
how hot do you run you CH boiler
John Rumm formulated the question :
IME many of the Vaillant boilers do support split temperature operation, but it does depends on what controls you have them paired with. The 400 series Vaillant I did (probably previous model range, since this was = 12 years ago), actually had separate knobs on the front for CH and DHW flow temperatures. Although that was retrofitted into system with traditional controls that could not distinguish between the source of the call for heat - hence the DHW control never came into play and it ran like your system does. The blurb on their web site: https://www.vaillant.co.uk/for-insta...ler-26116.html Seems to suggest its compatible with the VRC 700 weather compensating controls, so that ought to allow split temperature as well. I have studied it and not found any obvious way to split the temperature. I even spoke to Vailant and they confirmed there was no way it could be done. |
how hot do you run you CH boiler
On 12/01/2019 06:56, John Rumm wrote:
On 11/01/2019 22:25, wrote: On 11/01/2019 21:30, John Rumm wrote: On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as Indeed... 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period It might be required in particularly cold weather, but most of the time you will be able to use less. I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" You will most heat recovered from the condenser when the return temperature is below about 54 degrees (the dew point of the flue gasses). and the completely bogus "the temperature of the water in the radiators is set by the TRVs not the boiler temp.Â* I couldn't persuade the guy that he was taking bollox, he played the "I'm the experience heating engineer card and I know better than you" card. **** Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do I have weather compensation on mine, and so it chooses its own temperature based on the outside temp. Basically that means its runs as cool as it thinks it can get away with and still be able to reach the target set point temperature in a reasonable amount of time. (the relationship is set by choosing a mapping curve that reflects the rate of heat loss of the building). Currently the external temp is 6.5 deg C, and the flow temp is running at 54 deg. If it were to go well below 0, then it might push the flow temp up into the 70s. When its milder it might run flow temps down in the 40s. I thought the advice was to heat DHW to 60 degrees to avoid the risk of legionella, and that's not going to happen if the boiler's running at a lower temp. Oddly enough when I typed the reply above, I originally included discussion of DHW, however deleted it since I thought it was detail not required to answer the OP. Yup, the system runs higher flow temperatures for DHW reheat (or at least the later stages of them). It will modulate the flow temp during the process to achieve maximum condensation efficiency, while also ensuring good heat transfer rates). The coil in the cylinder will allow a recharge at a maximum rate of around 20 - 22kW - just a little bit less than the maximum output of the boiler. Does the boiler have an input to tell it that it's heating the DHW, or is the flow temperature adjusted automagically based on flow and return characteristics? I'm fairly certain that weather compensation isn't available for my W-B Greenstar 32/50 boiler, according to the book the manual adjustment range is 60-82C. Its a S plan+ system, but never actually runs he rads and DHW at the same time. My system is S+, but with Honeywell Evohome controls. Each room is a unique zone (2 zones in the bathrooms), with its own thermostat and time schedule. There is no "house" stat; the rads and DHW all operate independently of one another. I have it set to heat to 60 degrees for six days a week, and then it runs an anti legionella cycle one day a week, where it heats it to 70. Raising the temp to 70C for one day per week, and keeping it at 50C (say) at other times, seems like a damned good idea. I'll make the changes next time I'm fiddling with the settings. There is a TMV on the output of the cylinder to limit the maximum DHW temperature delivered to the points of use. I thought about a TMV when I planned the system but decided not to bother - perhaps an error. |
how hot do you run you CH boiler
On 12/01/2019 09:10, tim... wrote:
"Harry Bloomfield" wrote in message ... John Rumm pretended : It needs a little bit of experimentation to set the profile the first time - basically waiting for colder days and seeing if the system still heats the place comfortably and quickly enough. If it doesn't, then you just tweak it up to a steeper curve. It also helps if you have appropriate rad sizes for the rooms, and the system is balanced. Balanced? I have always assumed there was no need to balance a system, where TRV's are installed. if TRVs can be set to reliably keep a room at, say 20 degrees, then it doesn't but if they can't, then it does I'm about to find out if the first line is true, because it is clear than my new systems is not balanced. As it is currently set, the lounge is like a sauna, and the rest of the house still cool. I actually don't have a problem with the latter, it's the former that's the issue tim Where is the room stat? That is the big problem with TRVs, you have to have the system run whenever any rad wants heat and its difficult to impossible with only one room stat. Its a pretty crap way of doing it really. I have separate timer+stats on all the main rooms with 2 port valves. The valves have switches on them so they turn the boiler on if any of them is open. It costs more than TRVs but also saves money. The plumbers have trouble understanding stuff like that which is why they always go for TRVs as a second best option. |
how hot do you run you CH boiler
On 11/01/2019 23:33, Max Demian wrote:
On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. Which I thought far too high, as 1) it makes the radiators too hot to touch 2) basic thermodynamics suggest that a better temperature profile will result from having the radiators at the lower temperate for longer period than a higher temperature for a shorter period I tried to explain this but was met with "The recommended temperature is required for the condenser to have any effect" The instruction manual for my Ideal says that the 'e' setting is best for condensing, which is quite hot. I don't understand this as I would have thought that the cooler the returning water temperature the more condensing. Just found the manual for my Ideal Logic: "The Logic + Combi is a high efficiency combination boiler which is most efficient when operating in condensing mode. The boiler will operate in this mode if the CH temperature control (C) is set to the €˜e position (economy mode) or below. This control should be set to a maximum for very cold periods". I use a much lower temperature as I don't have a room thermostat and the TRVs are fiddly and don't seem to keep the air temperature constant. -- Cheers, Rob |
how hot do you run you CH boiler
On 11/01/2019 21:30, John Rumm wrote:
I have weather compensation on mine, and so it chooses its own temperature based on the outside temp. Basically that means its runs as cool as it thinks it can get away with and still be able to reach the target set point temperature in a reasonable amount of time. (the relationship is set by choosing a mapping curve that reflects the rate of heat loss of the building). Currently the external temp is 6.5 deg C, and the flow temp is running at 54 deg. If it were to go well below 0, then it might push the flow temp up into the 70s. When its milder it might run flow temps down in the 40s. Annoying Worcester do not have a simple weather comp option for theirs (you have to have the fancy controller and that precludes using your own heating controller, according to them). I oversized my rads as much as possible and I have been able to run on 64/54 in deep winter and 55/45 in the less cold parts of the year. -- Email does not work |
how hot do you run you CH boiler
On 12/01/2019 07:30, John Rumm wrote:
On 12/01/2019 00:55, RJH wrote: On 11/01/2019 21:30, John Rumm wrote: On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). Fitters told me that I should run this at 74 degrees. snip Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do I have weather compensation on mine, and so it chooses its own temperature based on the outside temp. Basically that means its runs as cool as it thinks it can get away with and still be able to reach the target set point temperature in a reasonable amount of time. (the relationship is set by choosing a mapping curve that reflects the rate of heat loss of the building). I don't follow how that can work properly, as for most homes different rooms will have a different 'curve'. Or does tweaking the TRV compensate? It seems to work well enough in practice. Each room also has a TRV, and I have the place split into two zones; upstairs and downstairs, so that will account for some variation. It needs a little bit of experimentation to set the profile the first time - basically waiting for colder days and seeing if the system still heats the place comfortably and quickly enough. If it doesn't, then you just tweak it up to a steeper curve. It also helps if you have appropriate rad sizes for the rooms, and the system is balanced. The response curves look like: http://wiki.diyfaq.org.uk/index.php/...tingCurve1.png IIRC the system defaults to the 1.2 line. If you live in a super insulted place / particularly sheltered location then you would tweak down. In my case (exposed location - solid wall construction), I needed to go up. I found the 1.8 curve worked well. The system is also smart enough to automatically shift the response curve vertically based on the currently demanded internal target temperature[1]: http://wiki.diyfaq.org.uk/index.php/...tingCurve2.png So if you tweak the room temp up or down during the day (or have different times programmed with different set point temps), then it can vary the flow temperature to match the requirement. [1] Note that all the system temperatures sensors (internal downstairs, internal upstairs, DHW cylinder, and external) are digitized and processed as actual temperatures, not just as on/off "call for heat" style demands. Thanks for that, interesting. And I hadn't realised such systems had a collection of sensors. OT but loosely relevant, I use my CH as 2 zones - upstairs and downstairs. I'm really not going to replumb to add a properly zones system, and I was wondering if it's possible to isolate the upstairs zone with a three way motorised valve - simply cutting out the upstairs 'circuit'. A single switch would be easier than faffing about with 4 TRVs each evening. -- Cheers, Rob |
how hot do you run you CH boiler
on 12/01/2019, dennis@home supposed :
Where is the room stat? My stat is in the hall and it is generally set to a lower temperature than we desire in the living room next to it. That is the big problem with TRVs, you have to have the system run whenever any rad wants heat and its difficult to impossible with only one room stat. Generally, if our hall is below temperature, other parts of the house will be too. So in practise it works pretty well. Its a pretty crap way of doing it really. It is a compromise of cost versus ideal with considerable extra complexity. Ideal is a zone per room, a temperature sensor per room and the means to use the data/ decide which rooms should be what temperature at what times of day, maybe to include occupation sensors. The boiler coming on if any zone requires heat input. |
how hot do you run you CH boiler
On 12/01/2019 09:09, Harry Bloomfield wrote:
After serious thinking harry wrote : TRVs don't work. They are more influenced by the nearby radiator temperature than the room air temp. You can get them with remote sensors. They work. They work absolutely fine here, once the heating has been on for a while and the system has settled down. I am able to log/graph room temperatures and once temperature is achieved, I only see variations of around 0.5C in the graphs. What TRV's or any type of stat cannot cope with is the overshoot, when the heating is suddenly turned on, or the stat suddenly turned up to a much higher setting. That's not a stat problem that's too much heat capacity in the radiators. The stat stops the flow but the stuff in the rad is too hot. You need to have low water content rads. |
how hot do you run you CH boiler
On 11/01/2019 23:48, Harry Bloomfield wrote:
If anyone knows a workaround, to allow split boiler output temperatures on this boiler - do let me know please. IIRC one of the add on controllers allows for different temps when running HW and heating but I don't recall which. |
how hot do you run you CH boiler
dennis@home explained :
That's not a stat problem that's too much heat capacity in the radiators. The stat stops the flow but the stuff in the rad is too hot. You need to have low water content rads. I agree, it was originally installed when the place had a much higher heat loss. Single glazed, no CWI, not much insulation in the roof and quite air leaky. But its a cost v benefit v need. Only one rad has needed to be changed and that swapped for one half the capacity, in the hall. The original boiler was around 32Kw, the new one 18Kw. The guy I got to install it, even suggested that was probably borderline too big, but I specced it. Too much capacity has the advantage that - Nudge the stat up a couple of degrees and it hits the selected new temperature very quickly. Then once up to temperature, it barely ticks over. |
how hot do you run you CH boiler
dennis@home brought next idea :
IIRC one of the add on controllers allows for different temps when running HW and heating but I don't recall which. It would have to be something which interacted directly with the boiler and Vailant said there was nothing able to do that, when I spoke to them. The boiler has the built in interfaces for the fancier control systems, I understand, but little detail to be found about these extra systems. |
how hot do you run you CH boiler
On 12/01/2019 10:03, wrote:
On 12/01/2019 06:56, John Rumm wrote: On 11/01/2019 22:25, wrote: On 11/01/2019 21:30, John Rumm wrote: On 11/01/2019 18:52, tim... wrote: I had a new Combi fitted today (in the to-be-moved-to house). [snip] Anyhow, at my current house it is 55 and works perfectly well what do you guys/galls do I have weather compensation on mine, and so it chooses its own [snip] Currently the external temp is 6.5 deg C, and the flow temp is running at 54 deg. If it were to go well below 0, then it might push the flow temp up into the 70s. When its milder it might run flow temps down in the 40s. I thought the advice was to heat DHW to 60 degrees to avoid the risk of legionella, and that's not going to happen if the boiler's running at a lower temp. Oddly enough when I typed the reply above, I originally included discussion of DHW, however deleted it since I thought it was detail not required to answer the OP. Yup, the system runs higher flow temperatures for DHW reheat (or at least the later stages of them). It will modulate the flow temp during the process to achieve maximum condensation efficiency, while also ensuring good heat transfer rates). The coil in the cylinder will allow a recharge at a maximum rate of around 20 - 22kW - just a little bit less than the maximum output of the boiler. Does the boiler have an input to tell it that it's heating the DHW, or is the flow temperature adjusted automagically based on flow and return characteristics? Yes ;-) The boiler knows what it is heating - you get a Tap logo pop up on its LCD rather than a radiator logo. The information is conveyed over its eBus rather than with a discrete input. Also like many boilers, it can adjust its power output based on a number of criteria including flow and return temps etc. I'm fairly certain that weather compensation isn't available for my W-B Greenstar 32/50 boiler, according to the book the manual adjustment range is 60-82C. ISTR that when I was looking for system boiler's that could do split temp, there were some options for some of the WB boilers. (I also considered paring a combi with an unvented cylinder, so one could have fast potable DHW to the kitchen which is on a long pipe run) Its a S plan+ system, but never actually runs he rads and DHW at the same time. My system is S+, but with Honeywell Evohome controls. Each room is a unique zone (2 zones in the bathrooms), with its own thermostat and time schedule. There is no "house" stat; the rads and DHW all operate independently of one another. I have it set to heat to 60 degrees for six days a week, and then it runs an anti legionella cycle one day a week, where it heats it to 70. Raising the temp to 70C for one day per week, and keeping it at 50C (say) at other times, seems like a damned good idea. I'll make the changes next time I'm fiddling with the settings. There is a TMV on the output of the cylinder to limit the maximum DHW temperature delivered to the points of use. I thought about a TMV when I planned the system but decided not to bother - perhaps an error. I was not that keen on the idea that some times it would otherwise deliver 70 degree water to the taps. Having a TMV on the cylinder output is a bit of a compromise, since it means you don't have the benefit of running the very hot water through all the pipe work like you would with multiple TMVs at every point of use. In the end I went for a high flow TMV, and set it at max temperature (about 55 IIRC). That allows for some heat loss in the pipes and still delivers water hot enough you can mix in some cold at the point of use - giving shower valves etc a bit more control. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
how hot do you run you CH boiler
On Sat, 12 Jan 2019 07:35:10 +0000, John Rumm wrote:
manual - adjust the flow temperature yourself in response to particularly cold days - probably works quite well for users who are clued up enough to understand the requirement. This is what I do. The boiler is in the downstairs loo at the back of the house, and I see it frequently! -- My posts are my copyright and if @diy_forums or Home Owners' Hub wish to copy them they can pay me £1 a message. Use the BIG mirror service in the UK: http://www.mirrorservice.org *lightning surge protection* - a w_tom conductor |
how hot do you run you CH boiler
In article ,
tim... wrote: Anyhow, at my current house it is 55 and works perfectly well You must have rather oversized rads? -- *Failure is not an option. It's bundled with your software. Dave Plowman London SW To e-mail, change noise into sound. |
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