I seem to recall this being a topic in the other place but cannot find the relevant details hence this post.
As part of this years drive to reduce the reliance on the LPG boiler for DHW I was planning in installing an inline electric heater on the boiler cold inlet pipe.
The question is where do you find the maximum recommended inlet water temperature for the boiler?? Its a Worcester Bosch Greenstar condensing boiler - no hot water tank - and whilst I have the manual I cant see the info I am after anywhere in the manual or fitting guide. I know the inlet section before the heat exchanger has a plastic section with a micro turbine which generates the "water flowing" signal for the boiler to light up and I am guessing this is the temperature critical component - anyone got any ideas?
Moxi
condensing boiler inlet water maximum temperature
Re: condensing boiler inlet water maximum temperature
I recall from the other place, the manufacturer wont tell you as they get concerned about legionella, rather than it will feck the boiler.
I also have a Worcester Bosch Greenstar condensing boiler and fitted a preheat water tank. I find that up to around 40 / 45 degrees inlet it works fine. At over 50 degrees the water temp in the gas boiler goes over 60 and shuts off for quite a while so you get fluctuating water temperatures.
So I used to fit a blending valve set to about 40 degrees, so I could heat the preheat tank up hotter with immersions powered by my solar diverters.
Now I have a larger pre-heat tank, I've done away with the blending valve, heat the tank to mid 40's with my heatpump, then either,
1) Run it through the gas combi boiler.
2) Or the gas boiler is switched off and I heat the pre-heat tank up further from mid 40's to low 50's with the immersion. Solar diverter in summer and off peak import in winter.
I no longer do (1) as the gas boiler was switched off apart from servicing end of last April and I think it will only be switched on again in an emergency.
I also have a Worcester Bosch Greenstar condensing boiler and fitted a preheat water tank. I find that up to around 40 / 45 degrees inlet it works fine. At over 50 degrees the water temp in the gas boiler goes over 60 and shuts off for quite a while so you get fluctuating water temperatures.
So I used to fit a blending valve set to about 40 degrees, so I could heat the preheat tank up hotter with immersions powered by my solar diverters.
Now I have a larger pre-heat tank, I've done away with the blending valve, heat the tank to mid 40's with my heatpump, then either,
1) Run it through the gas combi boiler.
2) Or the gas boiler is switched off and I heat the pre-heat tank up further from mid 40's to low 50's with the immersion. Solar diverter in summer and off peak import in winter.
I no longer do (1) as the gas boiler was switched off apart from servicing end of last April and I think it will only be switched on again in an emergency.
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Re: condensing boiler inlet water maximum temperature
Thanks Nowty,
As always you are a mine of good information, we run the shower direct off the boiler so I don't think we would be able to completely eliminate the boiler, I did drop on a small stainless steel 90 litre direct hot water cylinder for free but I need to construct an external plant room before I can even begin thinking about plumbing something like that in to the house DHW system (hold that thought theres a space under the stairs thats just come free, I wonder???). The cottage is really weird having been built in bits over the last 140 odd years, its got a wet central heating system that we use in winter once in the morning for half an hour otherwise its barely used and high on my list to be ripped out and replaced by electric slimline panels or something.
That leaves the kitchen and bathroom directly above both at the back of the house, kitchen supplies could easily be dealt with an under sink electric water heater single phase with say a 10 litre buffer tank or even a cooker style tap if funds stretch that far but the bathroom holds the large volume hot water demand requirement, the bath is very large being 100mm wider and 200mm longer than a standard bath - perfect for small children's indoor pool and tall wives and the shower, as far as I can see both still need the gas boiler subsidised so to speak by preheat until such time as instant electric boilers on single phase develop to a sensible flow point or I find a spot for a big hot water tank ?
Moxi
As always you are a mine of good information, we run the shower direct off the boiler so I don't think we would be able to completely eliminate the boiler, I did drop on a small stainless steel 90 litre direct hot water cylinder for free but I need to construct an external plant room before I can even begin thinking about plumbing something like that in to the house DHW system (hold that thought theres a space under the stairs thats just come free, I wonder???). The cottage is really weird having been built in bits over the last 140 odd years, its got a wet central heating system that we use in winter once in the morning for half an hour otherwise its barely used and high on my list to be ripped out and replaced by electric slimline panels or something.
That leaves the kitchen and bathroom directly above both at the back of the house, kitchen supplies could easily be dealt with an under sink electric water heater single phase with say a 10 litre buffer tank or even a cooker style tap if funds stretch that far but the bathroom holds the large volume hot water demand requirement, the bath is very large being 100mm wider and 200mm longer than a standard bath - perfect for small children's indoor pool and tall wives and the shower, as far as I can see both still need the gas boiler subsidised so to speak by preheat until such time as instant electric boilers on single phase develop to a sensible flow point or I find a spot for a big hot water tank ?
Moxi
Re: condensing boiler inlet water maximum temperature
In a condensing boiler, won't the efficiency of the boiler suffer if your return temps are too high?
I know little of gas boilers, other than that they're able to modulate, unlike oil ones.
Alternatively, what about seeking to reduce the inlet temperature of the gas boiler to its minimum recommended steady state temperature (specified in the manual?), and ask it to only achieve a flow temperature of a bit above that, which it should do by modulating. Then, boost the flow temperature further with your inline electric one - unlike the boiler, its efficiency won't drop so significantly at higher temps.
Plucking numbers out of the air, for example, temp into the boiler 40C, out of boiler and into electric heater 50C, out of electric heater 55C.
I know little of gas boilers, other than that they're able to modulate, unlike oil ones.
Alternatively, what about seeking to reduce the inlet temperature of the gas boiler to its minimum recommended steady state temperature (specified in the manual?), and ask it to only achieve a flow temperature of a bit above that, which it should do by modulating. Then, boost the flow temperature further with your inline electric one - unlike the boiler, its efficiency won't drop so significantly at higher temps.
Plucking numbers out of the air, for example, temp into the boiler 40C, out of boiler and into electric heater 50C, out of electric heater 55C.
Re: condensing boiler inlet water maximum temperature
GarethJ, pretty sure you are correct. BUT not sure if that only applies to the circulating water for the heating though, but I would assume it could/should also apply to the inlet temp for the DHW as well. In that case I think anything above around 50 deg C will stop the boiler operating in "condensing" mode and therefore reduce its efficiency.
Also at the flow rates required for DHW I don't think an "inline" electric heater is going to be that good. I would think longer term and get a large storage tank - call it what you want - thermal store or what ever, but get a big one with two immersions and for most of the year a decent amount of PV and a solar diverter will keep your boiler off - or look at heating it with a heat pump for better efficiency. I have a 300 odd litre tank and it used to suffice for 6 of us (when we were "lucky" enough to still have the kids living at home!).
Also at the flow rates required for DHW I don't think an "inline" electric heater is going to be that good. I would think longer term and get a large storage tank - call it what you want - thermal store or what ever, but get a big one with two immersions and for most of the year a decent amount of PV and a solar diverter will keep your boiler off - or look at heating it with a heat pump for better efficiency. I have a 300 odd litre tank and it used to suffice for 6 of us (when we were "lucky" enough to still have the kids living at home!).
Re: condensing boiler inlet water maximum temperature
I missed the DHW part!
My point isn't really relevant
My point isn't really relevant
Re: condensing boiler inlet water maximum temperature
Just how big an electric heater are you thinking of???
I'm assuming you're going for a fairly average flow rate (10 l/min), and that the specific heat capacity of water is 4.2 kJ/kg.K. This means at 1/6 litres/second (=kg/sec) you're going to need a power of 4.2/6 = 0.7 kW just to heat the water by 1°C. If you're thinking of this as a PV diverter, you're both perfectly safe and wasting your time so far as saving gas is concerned.
I'm assuming you're going for a fairly average flow rate (10 l/min), and that the specific heat capacity of water is 4.2 kJ/kg.K. This means at 1/6 litres/second (=kg/sec) you're going to need a power of 4.2/6 = 0.7 kW just to heat the water by 1°C. If you're thinking of this as a PV diverter, you're both perfectly safe and wasting your time so far as saving gas is concerned.
Re: condensing boiler inlet water maximum temperature
Sorry if i have missed this but I too have struggled to work out what the point of this is. When CH use gas +pv diverter, when no CH use inline +pv diverter.
Re: condensing boiler inlet water maximum temperature
Morning all,
Yes you are all arriving at the same point I have and which I alluded to in my reply to Nowty, DHW on an inline basis isn't practical on single phase with currently available domestic application technologies.
For shower or bath a large HWC is going to be required - not something we have and space wise not something we can easily see as being installed inside the cottage, lateral thinking may offer other unique solutions but these would need very careful consideration to ensure they would be fit for purpose.
The thing I hadn't really thought of previously but does offer a route to small volumes of DHW without much / any LPG is the under sink water heaters with small buffer tank and I will look more into this but also the real answer does seem to be one of two main options either
"find somewhere / someway" of introducing a large thermal store /HWC as part of the cottage DHW system in the future; or
investigate the practicality of having a three phase supply to the cottage for a 3 phase electric DHW boiler.
No idea how much a 3 phase supply would cost, my main concern is that it starts to tie me back to the grid supplies at a time when it feels like a retrograde step. Regards a HWC maybe I need to consider prices for bespoke shaped tanks that could fit an unusual positions and indeed which are aesthetically pleasing and can be on show rather than hidden away to see if that gives rise to any practical locations in the cottage?
Lots of food for thought - thanks
Moxi
Yes you are all arriving at the same point I have and which I alluded to in my reply to Nowty, DHW on an inline basis isn't practical on single phase with currently available domestic application technologies.
For shower or bath a large HWC is going to be required - not something we have and space wise not something we can easily see as being installed inside the cottage, lateral thinking may offer other unique solutions but these would need very careful consideration to ensure they would be fit for purpose.
The thing I hadn't really thought of previously but does offer a route to small volumes of DHW without much / any LPG is the under sink water heaters with small buffer tank and I will look more into this but also the real answer does seem to be one of two main options either
"find somewhere / someway" of introducing a large thermal store /HWC as part of the cottage DHW system in the future; or
investigate the practicality of having a three phase supply to the cottage for a 3 phase electric DHW boiler.
No idea how much a 3 phase supply would cost, my main concern is that it starts to tie me back to the grid supplies at a time when it feels like a retrograde step. Regards a HWC maybe I need to consider prices for bespoke shaped tanks that could fit an unusual positions and indeed which are aesthetically pleasing and can be on show rather than hidden away to see if that gives rise to any practical locations in the cottage?
Lots of food for thought - thanks
Moxi
Re: condensing boiler inlet water maximum temperature
Morning Ken,
the point for us is that if we cant buy a bottle of LPG then we don't have any way of getting hot water short of boiling a pan on the WBS or the cooker. Its never been an issue before as the LPG supply chain has been reliable - however - recently the bottled and bulk LPG market has seen some supply failures leaving people without heating or DHW for days and sometimes weeks, we have on occasion not had DHW at the tap for up to 4 days and now I am addressing some other shortcomings of the cottage with regard to electrical supply redundancy / self sufficiency I thought I should re-visit the DHW redundancy element too.
It does seem to me that the fundamental missing link is the HWC - in most modern properties with a HWC you have piped gas supplies which do not usually fail and if they do its usually quick to be reconnected, and as a back up theres the electric immersion heater as a source for a bulk supply of hot water.
So its either a HWC with two or three discrete heating inputs, an electrical in line boiler and diverse electrical supply, or a tin bath in front of the fire
All things appear to point to the common issue that alack of HWC is limiting options to provide meaningful DHW by other means so either i need to have more LPG bottles stored for "just in case" or find somewhere / someway of fitting a big enough HWC ?
Moxi
the point for us is that if we cant buy a bottle of LPG then we don't have any way of getting hot water short of boiling a pan on the WBS or the cooker. Its never been an issue before as the LPG supply chain has been reliable - however - recently the bottled and bulk LPG market has seen some supply failures leaving people without heating or DHW for days and sometimes weeks, we have on occasion not had DHW at the tap for up to 4 days and now I am addressing some other shortcomings of the cottage with regard to electrical supply redundancy / self sufficiency I thought I should re-visit the DHW redundancy element too.
It does seem to me that the fundamental missing link is the HWC - in most modern properties with a HWC you have piped gas supplies which do not usually fail and if they do its usually quick to be reconnected, and as a back up theres the electric immersion heater as a source for a bulk supply of hot water.
So its either a HWC with two or three discrete heating inputs, an electrical in line boiler and diverse electrical supply, or a tin bath in front of the fire
All things appear to point to the common issue that alack of HWC is limiting options to provide meaningful DHW by other means so either i need to have more LPG bottles stored for "just in case" or find somewhere / someway of fitting a big enough HWC ?
Moxi