To zone UFH or not to zone?

heavydawson

I've been getting quotes from a variety of GSHP installers, and while I've nearly settled on one, I've got a quick question on UFH.

One of the suppliers doesn't zone the house, and the others do.
This supplier suggested that the constant on and off of a zoned set up would reduce the life-span of the system. There's probably some truth in that, but I'm just wondering what peoples opinion on the matter is?

The house is being properly insulated with a minimum on-paper spec of a 0.12u (save for the windows) all-round envelope with proper detailing at all critical points, and will be looking to achieve a very high standard of air-tightness.

I can PM details of the supplier if they'd like to know more about the specific GSHP system I'm talking about. Both the supplier and system have had excellent feedback here on boards

soundskin

If going for a GSHP (depending on it's controls, should be weather compensating) then you will need a certain amount of your UFH to be 'open zoned'(i.e. no stats), usually the living areas. Therefore whenever the GSHP comes on due to a drop in temperature outside then you will always have an open area of UFH that can take heat from the GSHP. If this area isn't large enough then it can lead to cycling of the GSHP and therefore reduce it's lifespan.

If you then have thermostats or zoned control in bedrooms etc then you can keep these rooms at lower (~17 degrees) temperatures to the living (~20 degrees).

Even if you don't have any zoned control on your UFH then you can always regulate the flow rates to your rooms at the UFH manifold, therefore giving control over the room temperature in those individual room. All rooms have varying amounts of heat loss depending on size, external walls, fireplace, orientation etc, the more heat loss you have, the higher the flow rate required to that room, the lower the heat loss, the less flow rate required.

Normally the heat pump controls will be far more intelligent than a simple thermo/chronostat. These stats should really only be used in area that you want cooler that what the GSHP will keep the house, or rooms that have a second heat source (besides UFH) like a stove or fireplace.

Hope that helps.

heavydawson

soundskin wrote: »

If going for a GSHP (depending on it's controls, should be weather compensating) then you will need a certain amount of your UFH to be 'open zoned'(i.e. no stats), usually the living areas. Therefore whenever the GSHP comes on due to a drop in temperature outside then you will always have an open area of UFH that can take heat from the GSHP. If this area isn't large enough then it can lead to cycling of the GSHP and therefore reduce it's lifespan.

If you then have thermostats or zoned control in bedrooms etc then you can keep these rooms at lower (~17 degrees) temperatures to the living (~20 degrees).

Even if you don't have any zoned control on your UFH then you can always regulate the flow rates to your rooms at the UFH manifold, therefore giving control over the room temperature in those individual room. All rooms have varying amounts of heat loss depending on size, external walls, fireplace, orientation etc, the more heat loss you have, the higher the flow rate required to that room, the lower the heat loss, the less flow rate required.

Normally the heat pump controls will be far more intelligent than a simple thermo/chronostat. These stats should really only be used in area that you want cooler that what the GSHP will keep the house, or rooms that have a second heat source (besides UFH) like a stove or fireplace.

Hope that helps.

it does help indeed. thanks soundskin

JD6910

heavydawson wrote: »

I've been getting quotes from a variety of GSHP installers, and while I've nearly settled on one, I've got a quick question on UFH.

One of the suppliers doesn't zone the house, and the others do.
This supplier suggested that the constant on and off of a zoned set up would reduce the life-span of the system. There's probably some truth in that, but I'm just wondering what peoples opinion on the matter is?

The house is being properly insulated with a minimum on-paper spec of a 0.12u (save for the windows) all-round envelope with proper detailing at all critical points, and will be looking to achieve a very high standard of air-tightness.

I can PM details of the supplier if they'd like to know more about the specific GSHP system I'm talking about. Both the supplier and system have had excellent feedback here on boards

please PM me the supplier and system.

heavydawson

JD6910 wrote: »

please PM me the supplier and system.

PM Sent

PeteHeat

soundskin wrote: »

Therefore whenever the GSHP comes on due to a drop in temperature outside then you will always have an open area of UFH that can take heat from the GSHP. If this area isn't large enough then it can lead to cycling of the GSHP and therefore reduce it's lifespan.

Sorry, the above does not make sense to me, why should any heat source be activated by anything other than a call for for heat from within the building?

I can understand the wisdom behind timed step back thermostats in every room especially for underfloor heating, however using expensive fuel when everyone is comfortable seems like a waste.

Is the heat pump not an appliance that should do what it is told instead of dictating to the owner?

.

JD6910

PeteHeat wrote: »

Sorry, the above does not make sense to me, why should any heat source be activated by anything other than a call for for heat from within the building?

I can understand the wisdom behind timed step back thermostats in every room especially for underfloor heating, however using expensive fuel when everyone is comfortable seems like a waste.

Is the heat pump not an appliance that should do what it is told instead of dictating to the owner?

.

peteheat - this is exactly my gripe as well. i cannot understand a system that decides by itself to come on a 3am in the morning (or indeed anytime) and boost the entire house just because the temp drops - we will be all under the duvet at 3am and the Heatpump coming on of its own accord is madness i think.

i think we should be in control and decide when the house/house occupants want heat. if you are busy cooking in the evenings and the kitchen is warm, why would you want a heat pump kicking in!!! if you are away from the house - why would you want the HP kicking in!!!

is it just me - but im not sure i agree with the constant temp theory

PeteHeat

JD6910 wrote: »

peteheat - this is exactly my gripe as well. i cannot understand a system that decides by itself to come on a 3am in the morning (or indeed anytime) and boost the entire house just because the temp drops - we will be all under the duvet at 3am and the Heatpump coming on of its own accord is madness i think.

i think we should be in control and decide when the house/house occupants want heat. if you are busy cooking in the evenings and the kitchen is warm, why would you want a heat pump kicking in!!! if you are away from the house - why would you want the HP kicking in!!!

is it just me - but im not sure i agree with the constant temp theory

I have no problem with weather compensating thermostats in fact they can be a very good source of control for flow temperatures, a bit like automatic control of the temperature setting on a standard boiler.

Ideal for the older house (Pre 2008) which tends to have much higher heat loss than the new houses many which are being built with insulation levels that make the current building regs look like old news.

Every room can have a timed step back thermostat which can be set at the temperature the customer likes, for example during the day it can drop 1 > 2 degrees in the bedrooms or similar at night in the living areas.

With UFH it is important for the customer to understand the system needs more time to recover any lost temperature than a radiator system with oil or gas flow temperatures in excess of 70c.

Perhaps the idea is to remove the control from the customer who may not understand the recovery times?

A lot of heat pumps were sold on the basis that they use off peak or night rate for electricity, it appears that some have dropped that idea and instead of using buffer tanks have opted to use electricity 24 / 7 even heating rooms that don't need it.

.

JD6910

PeteHeat wrote: »

I have no problem with weather compensating thermostats in fact they can be a very good source of control for flow temperatures, a bit like automatic control of the temperature setting on a standard boiler.

Ideal for the older house (Pre 2008) which tends to have much higher heat loss than the new houses many which are being built with insulation levels that make the current building regs look like old news.

Every room can have a timed step back thermostat which can be set at the temperature the customer likes, for example during the day it can drop 1 > 2 degrees in the bedrooms or similar at night in the living areas.

With UFH it is important for the customer to understand the system needs more time to recover any lost temperature than a radiator system with oil or gas flow temperatures in excess of 70c.

Perhaps the idea is to remove the control from the customer who may not understand the recovery times?

A lot of heat pumps were sold on the basis that they use off peak or night rate for electricity, it appears that some have dropped that idea and instead of using buffer tanks have opted to use electricity 24 / 7 even heating rooms that don't need it.

.

so peteheat would you agree with a RAD system off a big buffer tank which will have multiply fuel sources such as solar, stove with back boiler, and oil or gas??? the theory is that the solar will do the hard work for free, stove will contribute to the buffer tank in the evenings when it is on and finally the gas boiler kicks in as and when it is needed. MHRV is also used to distribute warm air from wet rooms to bedrooms. surely this sytem allows the home owner control over costs and allows you turn the heating on and off when you want!!!!

soundskin

JD6910 wrote: »

peteheat - this is exactly my gripe as well. i cannot understand a system that decides by itself to come on a 3am in the morning (or indeed anytime) and boost the entire house just because the temp drops - we will be all under the duvet at 3am and the Heatpump coming on of its own accord is madness i think.

i think we should be in control and decide when the house/house occupants want heat. if you are busy cooking in the evenings and the kitchen is warm, why would you want a heat pump kicking in!!! if you are away from the house - why would you want the HP kicking in!!!

is it just me - but im not sure i agree with the constant temp theory

The advantage of weather compensation over s-plan heating controls (timeclock & thermostat) is that is a predictive control for house temperature instead of a reactive control that will will get a standard heating controls.

Traditional heating system sequence of events:
1. Outside temperature drops
2. More heat is lost through the walls & windows
3. Rooms get colder - which is detected by the room thermostat
4. Thermostat 'tells' the boiler to fire/work harder (if timeclock allows)
5. Rooms get warmer again

In the above example, it isn’t until stage 4 that the boiler gets any ‘feedback’ and is able to respond to changing conditions.
The chances are that at this stage, the householder will be feeling the cold and will turn the thermostat up even further - wasting even more fuel.
If the outside temperature rises, the boiler will not respond until the rooms have become uncomfortably warm - so in addition to
adjusting thethermostat, there’ll probably be the temptation to open some windows, releasing more heat and wasting more energy

Weather Compensation Control
1. Outside temperature drops - which is detected by outdoor sensor
2. HP/Boiler will come on sending heat into house
3. Radiators get warmer to compensate for heat lost*
4. Room temperature is maintained

Therefore weather compensation is only looking to send in just the right amount of heat into the building, no more nor no less to keep it at a contant temperature. Various forms of heat pumps then will have temperature set backs built in that will allow greater use of night rate electricity.

WCC (weather compensation controls) will always be looking at the outside temperature (main factor in heating demand of a building) and calculate a desired flow temperature into the UFH/rads, this calculated flow temperature will increase in cold weather and decrease in warm.

The WCC will them compare the actual flow temperature in the rads/ufh (which reflects building temp) and compare it with the desired flow temperature (based on outdoor temp and homeowner setting) and run the heat pump if deemed necessary.

WWC is the only cost efficient way to control UFH.

JD6910

And all this wcc is still happening when I am at work or tucked up in bed!!!!!

I have no doubt the wcc works if u want a constant temp but we think we want old school like we were raised!!!! Turn on heat when cold and when you are at home. Turn off heat when leaving the house!!!!

We are of this opinion because we are putting serious effort and money into insulation and airtightness and think we won't need very much heat to have the place comfortable.

I think geo and air to water may be an ideal on all the time system if the tiger was still roaring but the Celtic tiger is dead and heating on 24/7/365 is madness!!!! Speed the money on insulation and reduce the need for constant temp heat!!!!!

BryanF

JD6910 wrote: »

And all this wcc is still happening when I am at work or tucked up in bed!!!!!

I have no doubt the wcc works if u want a constant temp but we think we want old school like we were raised!!!! Turn on heat when cold and when you are at home. Turn off heat when leaving the house!!!!

We are of this opinion because we are putting serious effort and money into insulation and airtightness and think we won't need very much heat to have the place comfortable.

I think geo and air to water may be an ideal on all the time system if the tiger was still roaring but the Celtic tiger is dead and heating on 24/7/365 is madness!!!! Speed the money on insulation and reduce the need for constant temp heat!!!!!

May I ask are you building? What air-tightness, thermal envolpe spec and KWHR/m2 are you expecting?

JD6910

All living spaces south facing with glazing.narrow plan design - passive principles. 200mm pumped cavity, 200mm in floor. No thermal bridges etc.... Trying to make it as low energy as possible. Aiming for full airtightness from a reputable company.

PeteHeat

soundskin wrote: »

The advantage of weather compensation over s-plan heating controls (timeclock & thermostat) is that is a predictive control for house temperature instead of a reactive control that will will get a standard heating controls.

Traditional heating system sequence of events:
1. Outside temperature drops
2. More heat is lost through the walls & windows
3. Rooms get colder - which is detected by the room thermostat
4. Thermostat 'tells' the boiler to fire/work harder (if timeclock allows)
5. Rooms get warmer again

In the above example, it isn’t until stage 4 that the boiler gets any ‘feedback’ and is able to respond to changing conditions.
The chances are that at this stage, the householder will be feeling the cold and will turn the thermostat up even further - wasting even more fuel.
If the outside temperature rises, the boiler will not respond until the rooms have become uncomfortably warm - so in addition to
adjusting thethermostat, there’ll probably be the temptation to open some windows, releasing more heat and wasting more energy

Weather Compensation Control
1. Outside temperature drops - which is detected by outdoor sensor
2. HP/Boiler will come on sending heat into house
3. Radiators get warmer to compensate for heat lost*
4. Room temperature is maintained

Therefore weather compensation is only looking to send in just the right amount of heat into the building, no more nor no less to keep it at a contant temperature. Various forms of heat pumps then will have temperature set backs built in that will allow greater use of night rate electricity.

WCC (weather compensation controls) will always be looking at the outside temperature (main factor in heating demand of a building) and calculate a desired flow temperature into the UFH/rads, this calculated flow temperature will increase in cold weather and decrease in warm.

The WCC will them compare the actual flow temperature in the rads/ufh (which reflects building temp) and compare it with the desired flow temperature (based on outdoor temp and homeowner setting) and run the heat pump if deemed necessary.

WWC is the only cost efficient way to control UFH.

All of the above makes sense I have WCC on my own boiler but it's wood pellet with flow temperatures ranging from 70 > 85c not a low temperature system as I don't have UFH.

That said I would still like to be control room temperatures, as you know each system must suit the occupants, for example there are four rooms in my house that need a constant 23 > 25c, the main living area is fine at 21 > 22c and bedrooms at 19c with step back to 16c during the day, so I need more control than most.
.

soundskin

JD6910 wrote: »

And all this wcc is still happening when I am at work or tucked up in bed!!!!!

I have no doubt the wcc works if u want a constant temp but we think we want old school like we were raised!!!! Turn on heat when cold and when you are at home. Turn off heat when leaving the house!!!!

We are of this opinion because we are putting serious effort and money into insulation and airtightness and think we won't need very much heat to have the place comfortable.

I think geo and air to water may be an ideal on all the time system if the tiger was still roaring but the Celtic tiger is dead and heating on 24/7/365 is madness!!!! Speed the money on insulation and reduce the need for constant temp heat!!!!!

My point is weather comp is best suited for UFH. If you wish to be turning the heat on and off when best suits you the rads is what you want, heated by whatever means suits.

I agree that money spent on insulation is never wasted, it's saving you money in the long run.

Condenser

PeteHeat wrote: »

Sorry, the above does not make sense to me, why should any heat source be activated by anything other than a call for for heat from within the building?

I can understand the wisdom behind timed step back thermostats in every room especially for underfloor heating, however using expensive fuel when everyone is comfortable seems like a waste.

Is the heat pump not an appliance that should do what it is told instead of dictating to the owner?

.

It is only operated by the heat within the building but the heat required is always dependant on the heatlosses of the house. The higher the heat loss the more energy required in order to remain in stasis. This is what weather compensation does and does very well. You set the temp and the heatpump decides how much energy the house needs depending on outside temp (or in other words how fast you're losing it)

Saying heating rooms that don't require heat is a waste of money is a basic misunderstanding of thermal dynamics. You do not decide how energy moves within a building structure, temperature differentials do. You may not want to heat them but they cost you energy anyway by drawing heat from warmer rooms.

PeteHeat

Condenser wrote: »

It is only operated by the heat within the building but the heat required is always dependant on the heatlosses of the house. The higher the heat loss the more energy required in order to remain in stasis. This is what weather compensation does and does very well. You set the temp and the heatpump decides how much energy the house needs depending on outside temp (or in other words how fast you're losing it)

Saying heating rooms that don't require heat is a waste of money is a basic misunderstanding of thermal dynamics. You do not decide how energy moves within a building structure, temperature differentials do. You may not want to heat them but they cost you energy anyway by drawing heat from warmer rooms.

I have a good understanding of thermodynamics, I also understand that every person is different, using my own home as an example I have one person who needs room temperature at no less 23c preferably as high as 25c.

I feel my own bedroom is too warm at 19c and as far as heat loss goes I always have a window open regardless of the outside temperature and that goes back a very long time well before the person who needs 25c arrived in my home.

When dealing with a persons home we are usually dealing with a number of individuals, each has their own idea as to what the ideal temperature of their environment is, so we do our best to give them what they are comfortable with.

There is a transfer of heat from the warmer rooms to the cooler rooms, by having temperature controls in each room no heat is required in the rooms with the lower temperature setting, the room with the person who needs the high temperatures will require the heat lost to the cooler rooms to be replaced, the thermostat in that room will call for heat to replace the heat lost to the cooler rooms (simple thermodynamics).

We are not just dealing with the building we are trying to make peoples homes comfortable for every person who lives there.

We are also supposed to do that in the most energy efficient way possible, I believe the people should be able to have control over the environment they live in and to that they need temperature controls to prevent their environment being either too warm or too cold.
.

JD6910

peteheat - do you reckon the high efficency rads will work with the low temperature buffer system???
or will the system be high temperature?? i would imagine the solar will be low temp, stove high temp and the gas ????

air

The constant temp requirement is simply down to the response time of UFH.

It's fine saying you don't need heat at 3am when you're in bed or when you're out, but UFH has a large thermal mass of screed to heat up before this can start heating the air in the house.
This means that if you want your room to be up to temp at 8am you very well may need to start heating the screed at 3am (exact time dependent on numerous factors).

Weather based predictive controls make a lot of sense in conjunction with UFH for this reason, it helps to ensure that the house is up to temp when you want it - despite the slow response of UFH.

There will be increased looses with UFH during these long ramp up times, however I feel these are far outweighed by the positive benefits of UFH - especially in a well insulated house.

JD6910

air wrote: »

The constant temp requirement is simply down to the response time of UFH.

It's fine saying you don't need heat at 3am when you're in bed or when you're out, but UFH has a large thermal mass of screed to heat up before this can start heating the air in the house.
This means that if you want your room to be up to temp at 8am you very well may need to start heating the screed at 3am (exact time dependent on numerous factors).

Weather based predictive controls make a lot of sense in conjunction with UFH for this reason, it helps to ensure that the house is up to temp when you want it - despite the slow response of UFH.

There will be increased looses with UFH during these long ramp up times, however I feel these are far outweighed by the positive benefits of UFH - especially in a well insulated house.

air - i am planning on high efficiency rads throughout - NOT UFH. any thoughts on the solar, stove, gas boiler with a buffer tank system???

air

UFH is much better suited to a buffer tank system as it can make use of much lower temperature water.

Rads and UFH are both primarily convective heating systems, their power output is dictated by their surface area and the temp difference between their surface and the air.
The UFH has much greater surface area so can output far more power given the same circulation water temp.

If for example on an Autumn day, your solar manages to raise your buffer tank to 35 degrees during the day. You come home and want heat.
The rads would take forever to heat the house as the temperature difference is too low between the rads and the air in the house.
The UFH on the other hand has much greater surface area so can use this low temp water.

The same thing will happen every time you do a burn on the stove and heat the store fully.
The rads will perform well until the water in the store gets down to 45 degrees perhaps.
However the UFH will continue outputting useful heating power from the store water until it drops far lower - perhaps as low as 25 degrees.
So you'll get more useful heating for the house out of each stove burn with the UFH.

Regardless of what you use keep the buffer tank within the envelope of the house if you can so you get the benefit of any standing losses from it.

Finally "high efficiency" rads is a BS term IMO, every RAD ever manufactured is 100% efficient. Maybe they mean low volume for quick response (which will improve overall efficiency a negligible amount) but generally it's just marketing speak.

JD6910

air wrote: »

UFH is much better suited to a buffer tank system as it can make use of much lower temperature water.

Rads and UFH are both primarily convective heating systems, their power output is dictated by their surface area and the temp difference between their surface and the air.
The UFH has much greater surface area so can output far more power given the same circulation water temp.

If for example on an Autumn day, your solar manages to raise your buffer tank to 35 degrees during the day. You come home and want heat.
The rads would take forever to heat the house as the temperature difference is too low between the rads and the air in the house.
The UFH on the other hand has much greater surface area so can use this low temp water.

The same thing will happen every time you do a burn on the stove and heat the store fully.
The rads will perform well until the water in the store gets down to 45 degrees perhaps.
However the UFH will continue outputting useful heating power from the store water until it drops far lower - perhaps as low as 25 degrees.
So you'll get more useful heating for the house out of each stove burn with the UFH.

Regardless of what you use keep the buffer tank within the envelope of the house if you can so you get the benefit of any standing losses from it.

Finally "high efficiency" rads is a BS term IMO, every RAD ever manufactured is 100% efficient. Maybe they mean low volume for quick response (which will improve overall efficiency a negligible amount) but generally it's just marketing speak.

i think the plan is for the gas to kick in and heat the buffer tank water the last few degrees needed before sending it out to the rads?????

if we go with UFH we are going back to the constant temp theory and we will have a slow responding UFH system. the rads can be turned on and get a pretty much immediate response. during the summer months our heating will be OFF and the solar gain into the living areas, solar panels for hot water and MHRV system distribute hot air from wet rooms to bedrooms will do the requirments. IF needed, the stove could always be lit and get hot water from that too and/or the gas boiler on rads could also be turned on to give the place a boost!!! what you reckon guys????:rolleyes:

we are working on the theory that we only need heat from September to April max. the rest of the year the solar panels and solar gain and stove the odd evening will do the business. the gas boiler is always available to give us a boost if needed.

air

Yeah, that's fine using the gas to kick in, but it wouldn't need to kick in with UFH as there would already be usable heat in the store.

The whole rads vs UFH setup is as much down to lifestyle and personal preference as anything else and you need to weigh up the pros and cons for yourself and make a decision, which it sounds like you have. There's no right or wrong system.
Personally I like the idea of contant temp and UFH from a comfort point of view. I think a lot of the desire for fast response is based on people's experience of old houses that would be freezing upon coming home after a day out, not really relevant to life in a modern structure.

I would recommend though if you want the quick response approach, then don't bother linking the stove to the store and just link the stove's boiler directly to the heating system.
You won't be able to make use of low temp water in the store without UFH so not much point in having it at all tbh.

JD6910

air wrote: »

Yeah, that's fine using the gas to kick in, but it wouldn't need to kick in with UFH as there would already be usable heat in the store.

The whole rads vs UFH setup is as much down to lifestyle and personal preference as anything else and you need to weigh up the pros and cons for yourself and make a decision, which it sounds like you have. There's no right or wrong system.
Personally I like the idea of contant temp and UFH from a comfort point of view. I think a lot of the desire for fast response is based on people's experience of old houses that would be freezing upon coming home after a day out, not really relevant to life in a modern structure.

I would recommend though if you want the quick response approach, then don't bother linking the stove to the store and just link the stove's boiler directly to the heating system.
You won't be able to make use of low temp water in the store without UFH so not much point in having it at all tbh.

air - we are trying to avoid the constant temperature model therefore aiming for RADS - so therefore the gas will need to kick in when we want heat to deliver high temp to the RADS???

you are dead right - no new house will be freezing especially with the insualtion and airtightness levels!!!

if we dont link the stove to the buffer then the rads will be heated by the stove whether we want it or not.. i think???? the buffer allows us store the energy until we want it and we can decide if we want it for heat or hot water or perhaps a bath!!!! the super insualted buffer will keep the water for a day or two im being told??

the low temp water in the buffer will be raised by the stove and/or the gas via the triple coil... is this theory correct?

air

JD6910 wrote: »

air - we are trying to avoid the constant temperature model therefore aiming for RADS - so therefore the gas will need to kick in when we want heat to deliver high temp to the RADS???

That's your own decision ultimately, and will work

JD6910 wrote: »

if we dont link the stove to the buffer then the rads will be heated by the stove whether we want it or not.. i think????

Yes, but it will also heat the room that the stove is in.
I would have though you would want heat in the rads most of the time you want heat from the stove.

JD6910 wrote: »

the buffer allows us store the energy until we want it and we can decide if we want it for heat or hot water or perhaps a bath!!!! the super insulated buffer will keep the water for a day or two im being told??

Yes but a batch boiler would make a lot more sense if you want to burn and store energy. The buffer will certainly stay warm a while but will still have a reasonably large standing loss. A stove is going to take forever to heat a large buffer tank (typically 1000L +)

JD6910 wrote: »

the low temp water in the buffer will be raised by the stove and/or the gas via the triple coil... is this theory correct?

Yes, but there would possibly be useable energy in the buffer if you were using UFH.

You're getting a bit carried away with the technicalities, you need to question what you want a buffer for?

A buffer is normally used where you have a source of heat such as a gasification boiler that is used in a batch system and has a higher output than your ongoing heat load. It makes sense to burn, store the energy in the buffer and then release it from the buffer as needed.
UFH is suited to this model as it allows you to extract a large percentage of the energy from the buffer (eg when the water in the buffer is between 30 and 50 degrees).
You:
1. Do not intend to install underfloor heating
2. Will not have a heating system suited to the buffer, the stove will have a small output.

In my opinion you should install a buffer big enough for your hot water demands only - probably 300L max for an average home.
Anything larger and you are wasting your time, space in your house and your money.

To make it clear, IMHO:
Buffer + RADS makes no sense
Big Buffer + room stove makes no sense

My suggestion for you:
Triple coil heating cylinder sized for DHW needs - stove coil, solar coil, gas coil.
Gas / Oil (or whatever) boiler and stove joined using a manifold to CH system.
QED.
Forget about the buffer, it's doing nothing for you!!!

JD6910

air - because we plan to install circa 90 tubes of solar - we need the big buffer tank i think???
the large amount of solar is so that we try achieve and capture as much "free" solar energy as possible (thats the hard work done getting the water from cold to luke warm). the stove will be then only topping up this semi-warm solar water so we are not trying to heat 1000L of cold water with the stove.

i think the buffer is to act a thermal store or battery. the battery is then available for a day or two to do all the showers, baths, hot water needs and heating. we cant gaurantee the solar from day to day so by using a big buffer we capture as much as we can - while we can - make hay while the sun shines!!!

dont get me wrong - i would love to eleminate the buffer as it is a pricey item and i would love to install the minimum amount of solar - but i am going on what i am being told????? we obviously want to install the bare minimum system that will do the job!!! really appreciate your thoughts - keep em coming!!!!!!!!!

air

In my opinion you are wasting your time and money installing the additional solar tubes and buffer tank.

Install a domestic hot water tank / thermal store big enough for your domestic hot water needs and enough tubes to match (probably 40 max).

This "free" energy that you're looking to capture energy is not there 9 out of 10 days that you will want it. Buying the equipment to capture it that one day out of ten will cost you an arm and a leg - a complete and total waste of money.

JD6910

air wrote: »

In my opinion you are wasting your time and money installing the additional solar tubes and buffer tank.

Install a domestic hot water tank / thermal store big enough for your domestic hot water needs and enough tubes to match (probably 40 max).

This "free" energy that you're looking to capture energy is not there 9 out of 10 days that you will want it. Buying the equipment to capture it that one day out of ten will cost you an arm and a leg - a complete and total waste of money.

so you reckon - put in a "standard" gas central heating system with the normal amount of solar doing the hot water requirements and also connect the stove DIRECTLY to the heating system??????

lot to be said for this - simple, cheap and tried and tested!!!!!!!

PeteHeat

If you install a high temperature radiator system you need a flow temperature of minimum 70c, the return temperature of a correctly balanced system will be 50 > 55c.

If your proposed solar works to manufacturers best figures your buffer will reach about 60c on a good day, but there are few very good solar days especially between autumn and spring.

If we take the large buffer combine solar and your stove you may achieve a stored heat of 45 > 50c.

So even on the best day your gas boiler has to fire to satisfy one zone because your proposed rads do not suit the low temperature you have stored.

If you use a low temperature system which must not have a timer fitted the solar, stove and buffer will provide some value.

A low temperature system will cost more, the proper controls will cost more, my biggest concern reading your posts is no timer might cause you health problems.

Your home can be warm and comfortable to walk into anytime if and only if you allow the system (any system) to work properly, there is no point fitting all the bells and whistles designed for a low temperature system into a heating system that is designed for high temperatures.

What you have described to Air is not a buffer but an accumulator, a different beast, looks like a buffer but it's not a buffer and a really good one costs around €5,000.00, a middle of the road unit costs around €3,000
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air

JD6910 wrote: »

so you reckon - put in a "standard" gas central heating system with the normal amount of solar doing the hot water requirements and also connect the stove DIRECTLY to the heating system??????

lot to be said for this - simple, cheap and tried and tested!!!!!!!

Exactly. There was never anything much wrong with traditional heating systems apart from the fact that the houses they were installed in lost heat from all angles.
Your stove is unlikely to have enough power to heat all the radiators so I would link it to one zone only. Get somebody to calculate the size of this zone based on your stoves rated output.

heavydawson

JD6910 wrote: »

All living spaces south facing with glazing.narrow plan design - passive principles. 200mm pumped cavity, 200mm in floor. No thermal bridges etc.... Trying to make it as low energy as possible. Aiming for full airtightness from a reputable company.

Will you PM me the name of the airtightness company?