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Post by brummieboy on May 31, 2024 9:30:57 GMT
Most boilers now have modulating burners, which effectively is load compensation by any other name. Likewise with pumps, that vary speed commensurate with resistance. As TRV's close and flow is restricted, the pump will adapt itself to the circumstances, and the burner will then modulate to maintain the flow temperature. The problem with combis is that if there is a regular demand for hot water as in medium to high occupancy, whilst hot water is being supplied you have no heating. They are good in low occupancy (1 or 2 people) and smaller premises where heating is quickly responsive. A more efficient compromise is to have a combi with the dedicated DHW supply to kitchens and utilities, with the heating circuit valve controlled to a DHW cylinder closer to the bathrooms. This gives more responsive hot supply all through the house with less wasted water waiting for long hot runs to warm up, and when there is prolonged usage running baths or showers, the heating is not compromised. I think the main reason that such systems are not common is that the control concept is well outside the thought capability of the average plumber or electrician who have to combine and respect each others disciplines. In your mother's case, a wireless room stat would easily adapt to a better environment and take little wiring. The only problem with them for many older people is they tend to be digital and they do not have a knob to turn.
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Post by Telemachus on May 31, 2024 11:11:35 GMT
Most boilers now have modulating burners, which effectively is load compensation by any other name. Well I know you are the expert but I will have to disagree with you on this point. Basic burner modulation is used to maintain a constant output temperature in the face of varying loads eg TRVs shutting down, reduced heat loss from rads due to room heating up etc. This has been around for yonks, even our old boiler left over from the last century had that. Load compensation is where the output temperature is reduced as the set temp is approached. As you will know, a condensing boiler is much more efficient at lower flow temperatures. Weather compensation adds to this by including an element of outside temperature into deciding the flow temperature. Having the rads ticking over at say 40C is much more economical than having them cycle between say 65C and off. But on a very cold day you might need 65C to heat the room or at least get it up to temperature. Of course in order to have all that you need a modulating boiler as a starting point but I doubt you can get one that doesn't modulate these days.
Of course you can do this manually by adjusting the flow temperature, but most people don't bother.
But as I said, if you have load and weather compensation on a system boiler, it can give problems with low DHW temperatures and legionnaires risk. This is the bit I can't see how to solve, but maybe you only get load and Wx compensation on Combis? I like your idea of mixed combi and DHW tank but it creates the problem of low CH flow temperatures impacting the DHW temperature.
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Post by brummieboy on May 31, 2024 12:47:38 GMT
Most boilers now have modulating burners, which effectively is load compensation by any other name.
I like your idea of mixed combi and DHW tank but it creates the problem of low CH flow temperatures impacting the DHW temperature.
It is a question of 'cake and eat it'. As most systems don't have the radiator area for 40c tickover it is not a problem. As regards DHW, if you maintain 60c as the recommended anti legionaires temperature, then you need a flow temperature in excess of that. This was a grave omission by the advocates of low flow temperature advice to save energy costs. With the mixed option I quoted, if you still want to maintain a low heating temperature, you could always achieve this with an underfloor heating type mixing valve controlled circuit to maintain primary temperature at the cylinder. Most of my experience was with oil fired boilers and until you got to 500,000 Bthu's, modulation was not available, and even where it was it was a basic High/Low situation. All of this has contrived to make simple domestic heating much more complicated with higher installation and maintenance costs far outweighing any energy savings. It also creates more problems for the consumer who does not fully understand the operation of controls and takes his wallet in his hands to have the simplest faults rectified. I lost count of the number of programmable thermostats I replaced with timeclocks and dial thermostats for customers, not all seniors, who could not operate the sophisticated units. Many tears ago, I replaced our analogue 24 hour programmer with a new digital 7 day unit. The first question my wife asked was "Where is the overide button?"
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Post by Telemachus on May 31, 2024 13:23:22 GMT
Yes I should have said I was just talking about gas boilers. Reducing the flow temperature by means of a mixing valve wouldn't help as the temperature in the heat exchanger / flue gas exit temperature would still be high, there would be no improvement in economy.
What is needed is quite simple really, a system boiler with a diverter valve and 2 flow outputs, one for CH and one for DHW, and a control system that alternates between the two (if both circuits are calling for heat) and sets the flow temperature appropriate to which circuit the flow is going to. I don't think such a thing exists, which is a shame. But then again nearly everyone has a Combi these days and so the market would be very small. The HMI on mother's 3 channel 7 day controller is hideous, I need to read the manual if I need to change anything. Fortunately it seems to be reliable and has worked OK for 15 years or so. It does have 3 "advance" buttons which she knows how to use.
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Post by brummieboy on May 31, 2024 23:03:37 GMT
Most people do not have a combi, but with modern low water content heat exchangers, the amount of recirculated heat from a mixing valve would be very small, so the burner would stop. The residual heat in your 40c heating circuit would take a long time to cool significantly, and woulnot all be wasted as the mixing valve would use some of it. This is how underfloor heating works on a system boiler with a cylinder for hot water. With heat pumps on either UFH or radiators, 40cis about as high as you get and you have to supplement yor hot water with immersion heaters. Whilst some of what you say is relevant to commercial systems, on smaller domestic systems, in practice, optimisation and compensation is very overstated. Condensing boilers are more efficient, but the additional costs over what were high efficiency boilers or even standard efficiency like Clintons Worcester, coupled with increased service costs, there is very little or even no saving for the consumer in total spend. Government advisers who are mainly manufacturers are very persuasive to regulation makers who mostly do not understand what they are regulating. To 'prove' the savings of condensing gas boilers they used cast iron boilers to compare with low water content condensing boilers, and with oil boilers which still have heavy steel bodies, they downright lied to John Prescott who decreed what should happen. I have little more to add to this thread except to say to Clinton, if it aint broke, don't fix it.
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Post by Telemachus on May 31, 2024 23:17:55 GMT
The efficiency gains from low circulation temperature only happens at the burner/heat exchanger/flue. Cooler water in the heat exchanger means lower flue gas temperature ie you are pumping less heat into the atmosphere. And more water vapour condenses so you get the gain from the specific heat of condensation. Obviously one could have a hot boiler flow into the DHW tank and use a mixer to have lower radiator temperatures, but this would be fairly pointless as there would be no efficiency gain.
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Post by brummieboy on Jun 1, 2024 10:33:03 GMT
The calculation you need to do in assesing efficiency is to compare the heat input for a smaller quantity of water using reasonably sized emitters(radiators) to the amount of water at a lower temperature to feed a larger sized emitter, and maintain a comfortable ambient temperature. A comfortable ambient temperature is what every one wants, but I'm sure you also realise that such a thing is different things to different people. A radiator at 40c would need to be about 50-60% bigger to get anywhere close to achieving that level of comfort, particularly at start up, and there is evidence that lower temperatures cause problems with damp in the living areas, mainly because ventilation is restricted to conserve the perceived lower heat levels. Within domestic situations with underfloor heating, most, if not all installations, are supplemented with other direct appliances such as multifuel stoves. Within the industry there is much support to the old saying Bullshit Baffles Brains
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Post by Telemachus on Jun 1, 2024 14:59:28 GMT
The calculation you need to do in assesing efficiency is to compare the heat input for a smaller quantity of water using reasonably sized emitters(radiators) to the amount of water at a lower temperature to feed a larger sized emitter, and maintain a comfortable ambient temperature. A comfortable ambient temperature is what every one wants, but I'm sure you also realise that such a thing is different things to different people. A radiator at 40c would need to be about 50-60% bigger to get anywhere close to achieving that level of comfort, particularly at start up, and there is evidence that lower temperatures cause problems with damp in the living areas, mainly because ventilation is restricted to conserve the perceived lower heat levels. Within domestic situations with underfloor heating, most, if not all installations, are supplemented with other direct appliances such as multifuel stoves. Within the industry there is much support to the old saying Bullshit Baffles Brains Yes but this is where load and weather compensation comes in. At start up and when it’s cold outside, the system gives a high circulation temperature. If it is warm outside or once the room is up to temperature, a cooler flow is selected. A steady flow at 40c is more economical and more comfortable than an intermittent flow at 70C.
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Post by Jim on Jun 1, 2024 15:34:06 GMT
In the subject of radiator sizing, I'm knocking through kitchen wall in the bungalow, putting a new bigger rad in the living room, but sized according to a heat pump lower temp flow, so it won't need changing when we have a heat pump fitted in a few months. Stelrad do a calculator, input room area and flow temp.
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Post by Clinton Cool on Jun 1, 2024 15:51:39 GMT
In the subject of radiator sizing, I'm knocking through kitchen wall in the bungalow, putting a new bigger rad in the living room, but sized according to a heat pump lower temp flow, so it won't need changing when we have a heat pump fitted in a few months. Stelrad do a calculator, input room area and flow temp. Let me hazard a guess: tax payers are paying for the heat pump?
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Post by brummieboy on Jun 1, 2024 17:16:57 GMT
The calculation you need to do in assesing efficiency is to compare the heat input for a smaller quantity of water using reasonably sized emitters(radiators) to the amount of water at a lower temperature to feed a larger sized emitter, and maintain a comfortable ambient temperature. A comfortable ambient temperature is what every one wants, but I'm sure you also realise that such a thing is different things to different people. A radiator at 40c would need to be about 50-60% bigger to get anywhere close to achieving that level of comfort, particularly at start up, and there is evidence that lower temperatures cause problems with damp in the living areas, mainly because ventilation is restricted to conserve the perceived lower heat levels. Within domestic situations with underfloor heating, most, if not all installations, are supplemented with other direct appliances such as multifuel stoves. Within the industry there is much support to the old saying Bullshit Baffles Brains Yes but this is where load and weather compensation comes in. At start up and when it’s cold outside, the system gives a high circulation temperature. If it is warm outside or once the room is up to temperature, a cooler flow is selected. A steady flow at 40c is more economical and more comfortable than an intermittent flow at 70C. I am fullt conversant with the principles of optimisation and compensation which have been common in the field of commercial heating 60+ years, with the flow temperature being controlled by mixing valves. This has been adapted in smaller and domestic systems with modulating burners as you acknowledge above. Your claims about interment flows are a bit misleading. If there is a demand for heating in the space, there is no cessation of flow. The boiler thermostat controls the temperature of the primary water, but will maintain the flow temperature at an extremely steady level within 2 0r 3 degrees. Once the target space temperature is reached, then yes, the flow stops and will not restart until the room thermostat registers a demand. If you choose a lower flow temperature exactly the same things will happen. At a higher flow temperature the system is much more responsive and the level of comfort for the occupants is more readily felt. I realise as the fount of all knowledge you could no doubt design what you are claiming is inefficient, but by your own admissions, you're quite happy to leave your mother with a system that could easily be improved but you're happy to let her keep pressing the buttons on what sounds like Horstman 3XL programmer that you have dificulty in understanding even wiith your superior technical abilities. These will be my last words, but I realise you will have to have the very last word.
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Post by Telemachus on Jun 1, 2024 20:42:27 GMT
Yes but this is where load and weather compensation comes in. At start up and when it’s cold outside, the system gives a high circulation temperature. If it is warm outside or once the room is up to temperature, a cooler flow is selected. A steady flow at 40c is more economical and more comfortable than an intermittent flow at 70C. I am fullt conversant with the principles of optimisation and compensation which have been common in the field of commercial heating 60+ years, with the flow temperature being controlled by mixing valves. This has been adapted in smaller and domestic systems with modulating burners as you acknowledge above. Your claims about interment flows are a bit misleading. If there is a demand for heating in the space, there is no cessation of flow. The boiler thermostat controls the temperature of the primary water, but will maintain the flow temperature at an extremely steady level within 2 0r 3 degrees. Once the target space temperature is reached, then yes, the flow stops and will not restart until the room thermostat registers a demand. If you choose a lower flow temperature exactly the same things will happen. At a higher flow temperature the system is much more responsive and the level of comfort for the occupants is more readily felt. I realise as the fount of all knowledge you could no doubt design what you are claiming is inefficient, but by your own admissions, you're quite happy to leave your mother with a system that could easily be improved but you're happy to let her keep pressing the buttons on what sounds like Horstman 3XL programmer that you have dificulty in understanding even wiith your superior technical abilities. These will be my last words, but I realise you will have to have the very last word. You sound a bit sulky! There is obviously a big difference between industrial heating systems from 60 years ago, vs electronically controlled domestic system in the 2020s. I don’t think you understand the concept of condensing boilers and keeping the flow temperature low at the boiler, to improve efficiency. This has nothing to do with downstream mixing to reduce the temperature for eg under floor heating. The latter does nothing to improve boiler efficiency. It is all about the temperature actually in the boiler heat exchanger. A steady room temperature is achieved by have steady and warm rads. Not by having rads that alternate between hot and cold. And one doesn’t “select” a flow temperature, the system sets the flow temperature depending on circumstances, and varies it “on the hoof” according to circumstances. There, I’m glad we have sorted that out.
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Post by brummieboy on Jun 1, 2024 22:22:32 GMT
Not at all sulky. The principle of condensing boilers is that one has a differential between flow and return temperatures usually about 28c to enable the flue gassesto recover the latent heat. Aflow temperature of 40c would give you a much lower differential which is less efficient as their is less scope for heat recovert. I've yet to see a domestic gas boiler where one does not set the boiler temperature. All the advice from the energy advisers over the last year or two advises people to REDUCE THE BOILER TEMPERATURE to save costs.As explained before, the fact that the burner switches off at a set temperature does not interupt the flow through the radiators. Only when the room temperature is reached does that happen, and it also happens with low flow temperatures. I can understand you find this hard to understand when your misconstruction about my mentioning a heat anticipator being necessary in a mechanical room stat was the start of all this. Even when I explained it was only to ensure a positive operation on a bi metallic strip or gas bellows sensor, you still rambled off about excessive boiler cycling and continued to dig yourself deeper. There, I'm glad you've sorted it out.
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Post by Telemachus on Jun 1, 2024 23:10:35 GMT
Not at all sulky. The principle of condensing boilers is that one has a differential between flow and return temperatures usually about 28c to enable the flue gassesto recover the latent heat. Aflow temperature of 40c would give you a much lower differential which is less efficient as their is less scope for heat recovert. I've yet to see a domestic gas boiler where one does not set the boiler temperature. All the advice from the energy advisers over the last year or two advises people to REDUCE THE BOILER TEMPERATURE to save costs.As explained before, the fact that the burner switches off at a set temperature does not interupt the flow through the radiators. Only when the room temperature is reached does that happen, and it also happens with low flow temperatures. I can understand you find this hard to understand when your misconstruction about my mentioning a heat anticipator being necessary in a mechanical room stat was the start of all this. Even when I explained it was only to ensure a positive operation on a bi metallic strip or gas bellows sensor, you still rambled off about excessive boiler cycling and continued to dig yourself deeper. There, I'm glad you've sorted it out. The principle of condensing boilers is to have a lowish return flow temperature. The differential is not really relevant. The lowish return temperature means the flue gasses are cooled until the water vapour condenses, releasing the “latent heat of condensation” as “free” heat and thus increasing the efficiency. Condensing boilers only work in condensing mode when the return temperature is low. If you want a flow of say 80C and a return of say 60C, you will probably be above the condensing temperature and the boiler is no longer a condensing boiler (well, it is not on condensing mode). This is why condensing boilers quote efficiency at 80/60 (flow and return) and also at 50/30. The latter is much more efficient because the boiler is working in condensing mode, whereas at 80/60 it is not. I think you are not very up to date. Our gas boiler has no temp setting knob, although you can set the maximum flow temperature in the installer menus. There is a communications unit hard wired into the boiler via eBUS, it is Wi-Fi connected to the thermostat and the outside world and the phone app. It decides on the flow temperature, which will be hotter on a cold day and when there is a big difference between room and set temperature. Once everything is up to temperature the flow temp will be low such that the rads stay warm enough to keep the room at the correct temperature with pretty much zero fluctuation. The old CH was modulating but had a fixed flow temperature set on the boiler. The thermostat would click in and out and the radiator temperature would oscillate somewhat. It was ok for something designed in the last century, but the new system is much better. As to the heat anticipator, obviously I do understand how it works and what it is for. It is not rocket science. It makes the thermostat cycle more frequently in order to maintain a steadier room temperature, otherwise you would likely have a couple of degrees of oscillation. But it does this at the expense of cycling the heating system on and off. If there are no zone valves this may not matter too much but as I explained, in the case of my Mother’s system there are 3 zone valves. The thermostat only commands the zone valve to open or close. If a zone valve is open, a switch sends a signal to the boiler to fire. So if the thermostat is cycling frequently, the motorised zone valve is operating frequently. Every time it closes (and assuming the other circuits are off) the flow is stopped, the boiler is turned off and the pump run-on just circulates the flow through the automatic bypass valve. It does seem a fairly crap way of doing it but it seems to be standard practice in many systems. Or was, before load and weather compensation came in.
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Post by brummieboy on Jun 2, 2024 15:23:46 GMT
Not at all sulky. The principle of condensing boilers is that one has a differential between flow and return temperatures usually about 28c to enable the flue gassesto recover the latent heat. Aflow temperature of 40c would give you a much lower differential which is less efficient as their is less scope for heat recovert. I've yet to see a domestic gas boiler where one does not set the boiler temperature. All the advice from the energy advisers over the last year or two advises people to REDUCE THE BOILER TEMPERATURE to save costs.As explained before, the fact that the burner switches off at a set temperature does not interupt the flow through the radiators. Only when the room temperature is reached does that happen, and it also happens with low flow temperatures. I can understand you find this hard to understand when your misconstruction about my mentioning a heat anticipator being necessary in a mechanical room stat was the start of all this. Even when I explained it was only to ensure a positive operation on a bi metallic strip or gas bellows sensor, you still rambled off about excessive boiler cycling and continued to dig yourself deeper. There, I'm glad you've sorted it out. As to the heat anticipator, obviously I do understand how it works and what it is for. It is not rocket science. It makes the thermostat cycle more frequently in order to maintain a steadier room temperature, otherwise you would likely have a couple of degrees of oscillation. But it does this at the expense of cycling the heating system on and off. If there are no zone valves this may not matter too much but as I explained, in the case of my Mother’s system there are 3 zone valves. It does seem a fairly crap way of doing it but it seems to be standard practice in many systems. Or was, before load and weather compensation came in. Picking uo your one point, you obviously do not understand the action of the heat anticipator in a mechanical room stat. It simply makes a positive switch whereas without it, the contacts are likely to oscilate for a short period, especially with mains voltage which can arc a small gap. Most, virtually all popular ones from the last 7-8 years are rated A for efficiency. A modulating burner reduces the gas input in line with increasing return temperatures which is an accepted form of compensation, until the controls decide the room target temperature has been met when they switch off the boiler. In this condition your Vaillant all singing all dancing controler will do the same, except it apparently turns down the boiler thermostat to reduce flow temperatures. All boilers including yuors will have a boiler thermostat to set the flow temperature. Most of these are set within a digital panel programme but Ideal still do a knob which shows the temp in the panel. It is this temperature that we are advised to reduce to save energy, but obviously this will be noticeable to the occupants in cooler radiators. cooler radiators take longer to heat up a space although they will evetually get there depending on the insulation properties of the premises. There are products eg Nest, that will give you the oppotunity to remotely control your boiler and it is accepted that they do not 'talk the boiler's language' that they are about 1% less efficient than a boiler like your Vaillant. Industry tests put your boiler at abot 93-94%. An equivalent Worcester or Ideal shows up as about 92-93%. The link below makes interesting reading about the myths and let's say mistruths surrounding SEDBUK and Erp data. It also says that the most efficient flow temperature is 60-65oC with a return of 50oC. I would be wary of any return below 40oC as you may start getting condensation around the return port. Whilst it is not as destructive as it used to be on stee or cast heatexchangers, it can cause problems with sensors and control wiring. iheat.co.uk/boiler-help/energy-efficient-boilers
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