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  • FIRST POST
    • zeupater
    • By zeupater 21st Jul 13, 5:35 PM
    • 4,298Posts
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    zeupater
    Discussion ... ASHP(Air/Air) with Solar pv ....
    • #1
    • 21st Jul 13, 5:35 PM
    Discussion ... ASHP(Air/Air) with Solar pv .... 21st Jul 13 at 5:35 PM
    Hi All

    The combination of a small ASHP(Air/Air) with Solar pv seems to be a valid pairing of complementary technologies which has been raised a number of times on this forum.

    The idea of this thread is to encourage discussion of this combination in order to validate what an appropriate equipment specification would look like in order to maximise performance benefits in a typical domestic environment.

    Obviously, it is well understood that a typical domestic-scale solar pv system will not generate sufficient energy to provide winter heating, but should be considered as being a 'shoulder' months supplementary heat source for well insulated properties ... it is therefore best to concentrate on Spring & Autumn as being the target periods for heat provision, with an additional benefit of provision of cooling in heat-wave conditions such as we've been experiencing recently.

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
Page 13
    • zeupater
    • By zeupater 1st Aug 18, 10:15 PM
    • 4,298 Posts
    • 5,715 Thanks
    zeupater
    Hi All
    What is the best facing aspect to install ashp unit with regards the best cop of the unit.
    Originally posted by gefnew
    Hi

    I thought of this some time ago with respect to positioning the outdoor unit on/near a wall that had the best solar irradiance, but in the end decided that due to the unit airflow any potential gain would effectively be negligible for when we planned to use the system ...

    In reality if looking to provide heating in cold periods with relatively high humidity there's a logical argument that a south facing outdoor unit would need to enter the defrost cycle (slightly) less often, but for us it was far more important to have the indoor unit where we wanted it & keep the pipe runs reasonably short to reduce circuit inefficiencies (heat gain/loss) which is far more relevant, so it's on a roughly NW facing wall.

    HTH
    Z
    Last edited by zeupater; 02-08-2018 at 1:42 PM. Reason: -l +it
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    • ASavvyBuyer
    • By ASavvyBuyer 2nd Aug 18, 8:19 AM
    • 872 Posts
    • 2,555 Thanks
    ASavvyBuyer
    Hi

    I thought of this some time ago with respect to positioning the outdoor unit on/near a wall that had the best solar irradiance, but in the end decided that due to the unit airflow any potential gain would effectively be negligible for when we planned to use the system ...

    In really if looking to provide heating in cold periods with relatively high humidity there's a logical argument that a south facing outdoor unit would need to enter the defrost cycle (slightly) less often, but for us it was far more important to have the indoor unit where we wanted it & keep the pipe runs reasonably short to reduce circuit inefficiencies (heat gain/loss) which is far more relevant, so it's on a roughly NW facing wall.

    HTH
    Z
    Originally posted by zeupater

    Ours is the same, with the outside unit mounted in the place with the shortest run of pipes to the internal unit. It is on a sheltered East facing wall.
    Rhondda Cynon Taf, 4kWp, W roof, 30 pitch, 16 x 8.33 Eternity 250w E+10 panels, Solar Edge SE4000-16A Inverter + P300 Optimisers. Inst Aug 2015.
    + REUK Diverter & Toshiba RAS-10G2KVP-E Ultra High Efficiency Air Conditioner/Heat Pump. 100% Green Tariff. Kia Soul EV
    • gefnew
    • By gefnew 2nd Aug 18, 8:23 AM
    • 110 Posts
    • 123 Thanks
    gefnew
    Hi Z
    Thanks for your input, have a choice of south north west external walls.
    The house is a bungalow so the unit would have very short pipe runs.
    The living room is approx. 45 sqm which has west and north facing walls.
    Regards
    gefnew
    • gefnew
    • By gefnew 4th Aug 18, 9:19 AM
    • 110 Posts
    • 123 Thanks
    gefnew
    hi all
    I know you all like figures and stats, here a link to a five year ashp
    in Glasgow.
    http://www.alastairmcintosh.com/general/energy/solar-heating.htm
    maybe of interest.
    regards
    gefnew
    • Coastalwatch
    • By Coastalwatch 7th Sep 18, 9:08 PM
    • 200 Posts
    • 744 Thanks
    Coastalwatch
    So, having read this entire thread through on more than one occasion Im more than convinced and have taken the giant leap of enquiring for a quotation to install two single split ASHP systems as per the thread discussion. One for the lounge and one for the bedroom. I had initially suggested a multi split system, but was advised that two singles would be cheaper to install, (and probably cheaper to run also). The quote will include Daikin units as per the installers preference. In his experience these being very reliable and Id no knowledge to suggest otherwise. I note that Toshiba have been preferred here and have no idea how the Daikin units might perform in comparison?

    As weve a gas combination boiler, no immersion tank and loads of unused solar energy then I also asked to be quoted for the installation of a direct, unvented 170 litre hot water tank. The other incentive for this being that the boiler is placed at the opposite end of our bungalow to the kitchen with some fifty feet of pipe run between. The bathroom being midway between the two, with the old airing cupboard adjacent to it. Thus having the immersion in here, not only utilises some of the excess solar but also reduces the run for hot water when turning taps on and running a bath or shower. The installer asked if I should consider heating the tank from the gas boiler as well for the times when solar wasnt available? I hadnt considered this as assumed if solar wasnt available wed simply run directly from the combination boiler instead, but agreed for him to quote for this option as well.

    Im struggling to understand whether heating the hot water tank from the combination boiler makes any sense. I can see we should have plenty of hot water close to the bathroom but surely at some financial cost, admittedly heated by gas as opposed to grid electric, which I still feel rather defeats having the water heated as and when you need it!

    While the manufacturers warranty period will cover the units Im curious as to what period I should expect to be covered on the installation as a whole!

    If anyone has any thoughts or advice on the above then Ill certainly be pleased to hear back from you.
    East coast, lat 51.97. 8.26kw SSE, 23 pitch + 0.59kw WSW vertical. Nissan Leaf plus one dirty diesel. Still waiting for V2H and home storage to become available at sensible cost.
    • Coastalwatch
    • By Coastalwatch 11th Sep 18, 10:06 AM
    • 200 Posts
    • 744 Thanks
    Coastalwatch
    Im struggling to understand whether heating the hot water tank from the combination boiler makes any sense. I can see we should have plenty of hot water close to the bathroom but surely at some financial cost, admittedly heated by gas as opposed to grid electric, which I still feel rather defeats having the water heated as and when you need it!

    If anyone has any thoughts or advice on the above then Ill certainly be pleased to hear back from you.
    Originally posted by Coastalwatch
    Having rumenated over the problem for a few more days I can see that it really doesn't make sense. Firstly it's an additional use of a FF, which rather defeats the object of being green and ethical. It's wasteful, in that the tank loses 2 kWh energy per day(sort of ok when it's free solar, but probably not when burning a FF) and if/when home storage or V2H arrive at a cost effective price then being heated by gas would no longer be viable!

    So, I've eventually made my decision which just leaves me to thank you all for your patience in allowing me to do so.
    East coast, lat 51.97. 8.26kw SSE, 23 pitch + 0.59kw WSW vertical. Nissan Leaf plus one dirty diesel. Still waiting for V2H and home storage to become available at sensible cost.
    • Rodders53
    • By Rodders53 11th Sep 18, 5:44 PM
    • 490 Posts
    • 328 Thanks
    Rodders53
    As weve a gas combination boiler, no immersion tank and loads of unused solar energy then I also asked to be quoted for the installation of a direct, unvented 170 litre hot water tank.
    <snip>
    The installer asked if I should consider heating the tank from the gas boiler as well for the times when solar wasnt available? I hadnt considered this as assumed if solar wasnt available wed simply run directly from the combination boiler instead, but agreed for him to quote for this option as well.
    Originally posted by Coastalwatch
    How are you going to feed hot water from the combi into the new hot water tank outlet? and how is it going to know that the new HW tank's is depleted enough to need to run and supply hot water to the house?

    My guess is your Boiler man was suggesting you turn the Combi into a system boiler and heat the tank if you wish via a timer.
    I'd be pretty sure he intends to disconnect the HW out from the combi and disable that side anyway. The alternative would be a complex set of (motorised or) manual hot water changeover valves (with interlocks and other safety features)?
    • zeupater
    • By zeupater 11th Sep 18, 8:52 PM
    • 4,298 Posts
    • 5,715 Thanks
    zeupater
    How are you going to feed hot water from the combi into the new hot water tank outlet? and how is it going to know that the new HW tank's is depleted enough to need to run and supply hot water to the house?

    My guess is your Boiler man was suggesting you turn the Combi into a system boiler and heat the tank if you wish via a timer.
    I'd be pretty sure he intends to disconnect the HW out from the combi and disable that side anyway. The alternative would be a complex set of (motorised or) manual hot water changeover valves (with interlocks and other safety features)?
    Originally posted by Rodders53
    Hi

    Looks like the decision's been made on cost & preferred technology grounds, but (from a logical lay-person's viewpoint) I can't really see an issue with heating a DHW water storage cylinder with a thermostat as opposed to a set of radiators - I would have thought that it's a case of some rearranged pipework, a three way motorised valve (or two 2 way valves) & a new programmable controller to control water as that probably provides the simplest solution ... if the boiler needs to have a DHW feed there's always the possibility of hooking it up to provide hot water to a single sink in the utility (for example) ...

    Anyway, as mentioned, it looks like the preference is to not waste money at the moment & wait for battery storage prices to fall to a point where smart-controls and either a home battery or V2G linked to solar and off-peak tariff electricity provides an affordable & workable year-round solution ...

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    • Exiled Tyke
    • By Exiled Tyke 11th Sep 18, 11:17 PM
    • 270 Posts
    • 837 Thanks
    Exiled Tyke
    Hi

    Looks like the decision's been made on cost & preferred technology grounds, but (from a logical lay-person's viewpoint) I can't really see an issue with heating a DHW water storage cylinder with a thermostat as opposed to a set of radiators - I would have thought that it's a case of some rearranged pipework, a three way motorised valve (or two 2 way valves) & a new programmable controller to control water as that probably provides the simplest solution ... if the boiler needs to have a DHW feed there's always the possibility of hooking it up to provide hot water to a single sink in the utility (for example) ...

    Anyway, as mentioned, it looks like the preference is to not waste money at the moment & wait for battery storage prices to fall to a point where smart-controls and either a home battery or V2G linked to solar and off-peak tariff electricity provides an affordable & workable year-round solution ...

    HTH
    Z
    Originally posted by zeupater
    My experience is that this is not a good idea for two reasons:

    1. most combi boilers havea a higher output for direct hot water than for the radiators. So some of the capacity of the boiler is simply lost by not using it for the job that it is designed to do.
    2. Unless you set the timings to be different (which sometimes is impractical - e.g. you want the hot water heating up on a morning at about the same time as needing the house heating up ready for everyone getting up) then the boiler will be attempting to heat the house and the hot water at the same time, so doing neither job particularly well.

    So the effectively reduced output boiler is heating up a large quantity of water all in one go (and probably more than is really needed, just in case) at the same time as trying to heat the house. I suppose what I'm saying is you need a bigger boiler to do the job properly (which of course does not make financial sense). Of course if the combi boiler is already a much higher spec than the house actually needs then these problems may not arise.
    Install 28th Nov 15, 3.3kW, (11x300LG), SolarEdge, SW. W Yorks.
    • Coastalwatch
    • By Coastalwatch 12th Sep 18, 11:31 AM
    • 200 Posts
    • 744 Thanks
    Coastalwatch
    Thanks all for your time and comments, it is much appreciated. If I hadn't already arrived at the conclusion I had then, for sure, far more rumenating would have ensued.
    East coast, lat 51.97. 8.26kw SSE, 23 pitch + 0.59kw WSW vertical. Nissan Leaf plus one dirty diesel. Still waiting for V2H and home storage to become available at sensible cost.
    • zeupater
    • By zeupater 12th Sep 18, 2:46 PM
    • 4,298 Posts
    • 5,715 Thanks
    zeupater
    My experience is that this is not a good idea for two reasons:

    1. most combi boilers havea a higher output for direct hot water than for the radiators. So some of the capacity of the boiler is simply lost by not using it for the job that it is designed to do.
    2. Unless you set the timings to be different (which sometimes is impractical - e.g. you want the hot water heating up on a morning at about the same time as needing the house heating up ready for everyone getting up) then the boiler will be attempting to heat the house and the hot water at the same time, so doing neither job particularly well.

    So the effectively reduced output boiler is heating up a large quantity of water all in one go (and probably more than is really needed, just in case) at the same time as trying to heat the house. I suppose what I'm saying is you need a bigger boiler to do the job properly (which of course does not make financial sense). Of course if the combi boiler is already a much higher spec than the house actually needs then these problems may not arise.
    Originally posted by Exiled Tyke
    Hi

    Yes, but if the boiler already exists the question revolves around simply changing the pipework to accommodate the cylinder and installing a 3-way valve being a cheaper alternative to replacing the entire system .. after-all, that's the situation described ...

    From the referenced post it looks like the point has been missed ... a situation exists where due to there being no DHW storage it's currently impossible to use proportional diversion to heat water from an installed solar array, so in the case where a DHW cylinder is installed what would the fallback heat source be when a number of consecutive dull days impact on PV generation, and of course when daily generation if poor in the winter months ....

    We live with the very issue as we already have solar thermal for the DHW, however with our storage being around double that being considered by Costalwatch we have the ability to cope with a longer poor weather period before needing to use a secondary heat-source (ours is standard boiler GCH to a secondary cylinder coil heating the upper portion of a high insulation solar DHW cylinder) , but that simply effects the frequency of heat provision ...

    On heating water with the boiler (point 2) ... with a 3 way valve setup if there's demand from space heating and DHW then the installer has the ability to design & set the priority - water or heating, or potentially both - however, it's unlikely to really be an issue as a proposed 170l cylinder would only require around 10kWh to heat from completely cold, so around 5kWh as a top-up to whatever has been collect through solar diversion should be more typical, which should be much of an issue as the heat-transfer is a factor of boiler flow/temperature and cylinder coil surface area ... of course, it's also typical for solar diversion to be topped-up in the evening after sunset on a timed & thermostatic basis which can be scheduled for after the space heating requirement has reduced & the boiler has pre-heated the pipe-work & raised room temperatures ... then again, there's nothing to stop anyone doing this manually as required by flicking a switch!

    Anyway, it's not an issue as a decision has already been made! ...

    HTH
    Z
    Last edited by zeupater; 12-09-2018 at 2:48 PM.
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    • Exiled Tyke
    • By Exiled Tyke 12th Sep 18, 4:55 PM
    • 270 Posts
    • 837 Thanks
    Exiled Tyke
    Hi

    Yes, but if the boiler already exists the question revolves around simply changing the pipework to accommodate the cylinder and installing a 3-way valve being a cheaper alternative to replacing the entire system .. after-all, that's the situation described ...

    From the referenced post it looks like the point has been missed ... a situation exists where due to there being no DHW storage it's currently impossible to use proportional diversion to heat water from an installed solar array, so in the case where a DHW cylinder is installed what would the fallback heat source be when a number of consecutive dull days impact on PV generation, and of course when daily generation if poor in the winter months ....

    We live with the very issue as we already have solar thermal for the DHW, however with our storage being around double that being considered by Costalwatch we have the ability to cope with a longer poor weather period before needing to use a secondary heat-source (ours is standard boiler GCH to a secondary cylinder coil heating the upper portion of a high insulation solar DHW cylinder) , but that simply effects the frequency of heat provision ...

    On heating water with the boiler (point 2) ... with a 3 way valve setup if there's demand from space heating and DHW then the installer has the ability to design & set the priority - water or heating, or potentially both - however, it's unlikely to really be an issue as a proposed 170l cylinder would only require around 10kWh to heat from completely cold, so around 5kWh as a top-up to whatever has been collect through solar diversion should be more typical, which should be much of an issue as the heat-transfer is a factor of boiler flow/temperature and cylinder coil surface area ... of course, it's also typical for solar diversion to be topped-up in the evening after sunset on a timed & thermostatic basis which can be scheduled for after the space heating requirement has reduced & the boiler has pre-heated the pipe-work & raised room temperatures ... then again, there's nothing to stop anyone doing this manually as required by flicking a switch!

    Anyway, it's not an issue as a decision has already been made! ...

    HTH
    Z
    Originally posted by zeupater
    Just to clarify. My point was that using a combi boiler to heat a cylinder is not terribly effective as it's not been designed to do this job. I lived with this arrangement for a few years and it was an absolute pain in the neck.

    But as you say, not really relevant to this particular decision now.
    Install 28th Nov 15, 3.3kW, (11x300LG), SolarEdge, SW. W Yorks.
    • Coastalwatch
    • By Coastalwatch 13th Sep 18, 1:14 PM
    • 200 Posts
    • 744 Thanks
    Coastalwatch
    Just to clarify. My point was that using a combi boiler to heat a cylinder is not terribly effective as it's not been designed to do this job. I lived with this arrangement for a few years and it was an absolute pain in the neck.

    But as you say, not really relevant to this particular decision now.
    Originally posted by Exiled Tyke

    Thanks for further hypotheses chaps, I can just about follow what is being suggested. The jury is still out on how the plumbing will be sorted as I'll leave it to the professional who'll install it. From my point I wish to get the hotwater tank up and running on Solar energy only with the option of switching/isolating it to run the hot water direct from the gas combi boiler when the tank temperature isn't hot enough.

    According to pvgis there are just three months each year when there will not be in excess of 6 kWh spare daily from which to heat it. Understanding that added to this will be days of poor generation until a suitable sized storage battery(or EV) can be utilised to cover for them.

    From my simple viewpoint this option should derive the least capital outlay and running cost
    .
    As usual I'm open to be persuaded otherwise if a greener and/or more cost efficient method is readily practised.
    East coast, lat 51.97. 8.26kw SSE, 23 pitch + 0.59kw WSW vertical. Nissan Leaf plus one dirty diesel. Still waiting for V2H and home storage to become available at sensible cost.
    • ASavvyBuyer
    • By ASavvyBuyer 15th Sep 18, 7:33 AM
    • 872 Posts
    • 2,555 Thanks
    ASavvyBuyer
    Thanks for further hypotheses chaps, I can just about follow what is being suggested. The jury is still out on how the plumbing will be sorted as I'll leave it to the professional who'll install it. From my point I wish to get the hotwater tank up and running on Solar energy only with the option of switching/isolating it to run the hot water direct from the gas combi boiler when the tank temperature isn't hot enough.

    According to pvgis there are just three months each year when there will not be in excess of 6 kWh spare daily from which to heat it. Understanding that added to this will be days of poor generation until a suitable sized storage battery(or EV) can be utilised to cover for them.

    From my simple viewpoint this option should derive the least capital outlay and running cost
    .
    As usual I'm open to be persuaded otherwise if a greener and/or more cost efficient method is readily practised.
    Originally posted by Coastalwatch
    We have a hot water cylinder with an immersion heater and also a combi boiler.
    The plumbing is done so that in the winter we use the combi, but in the summer we use the hot water tank.
    Changeover is done by opening and closing some isolator valves so that the hot water supply is either direct from the combi or the hot water tank.
    We usually get all the solar PV heated water we need from May till September and switch over when we notice that there is not enough supplus to get the tank upto temperature.
    Rhondda Cynon Taf, 4kWp, W roof, 30 pitch, 16 x 8.33 Eternity 250w E+10 panels, Solar Edge SE4000-16A Inverter + P300 Optimisers. Inst Aug 2015.
    + REUK Diverter & Toshiba RAS-10G2KVP-E Ultra High Efficiency Air Conditioner/Heat Pump. 100% Green Tariff. Kia Soul EV
    • Coastalwatch
    • By Coastalwatch 17th Sep 18, 11:18 PM
    • 200 Posts
    • 744 Thanks
    Coastalwatch
    We have a hot water cylinder with an immersion heater and also a combi boiler.
    The plumbing is done so that in the winter we use the combi, but in the summer we use the hot water tank.
    Changeover is done by opening and closing some isolator valves so that the hot water supply is either direct from the combi or the hot water tank.
    We usually get all the solar PV heated water we need from May till September and switch over when we notice that there is not enough supplus to get the tank upto temperature.
    Originally posted by ASavvyBuyer
    Thanks ASB that's the style of system I have in mind with perhaps switching more frequently than just the once in spring and autumn depending on water temperature come the hours of darkness on a daily basis!

    Strangely, since his visit I've heard nothing further from the prospective installer, so it looks like I'll be seeking alternative quotations hoping eventually they will actually result in seeing the task through to completion.
    East coast, lat 51.97. 8.26kw SSE, 23 pitch + 0.59kw WSW vertical. Nissan Leaf plus one dirty diesel. Still waiting for V2H and home storage to become available at sensible cost.
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