T50 on new install?

[siricosm]

I am about to replace my radiators (and piping) and doing the heat loss calculations. I am wondering if the T50 rating on radiators is still reasonable. Wouldn't T40 be more efficient with today's boilers, or would the difference be hardly noticeably?

I guess T40 would also be at the upper limit of what you could use with a heat pump, which could be an issue if(when?) the government starts to apply pressure to get rid of gas boilers.

What would you use in your own house, if installing a new system from scratch? I am not interested in underfloor heating.

 

[SimonG]

I would always want slightly oversized rads. Controlled on the trv. Easier to turn down if too warm but nowhere to go if too cold.

 

[ShaunCorbs]

If you have the space for the size increase why not

 

[Knappers]

Keep an eye on total volume and expansion requirement

 

[siricosm]

Keep an eye on total volume and expansion requirement

I am planning on using cast iron rads and a thermal store, so the expansion is going to be way more than the vessel in a combi. This is yet another part I don't need.

Surprisingly, regular boilers are even more expensive than system boilers.

Boilers are like bikinis, the less you get, the more you pay.

 

[ShaunCorbs]

Things have moved where 15 years ago heat only boiler was standard ish now not many are getting installed compared to combis

 

[siricosm]

I am planning on using cast iron rads, which are not cheap. So at T40 I would need 1.6x the wattage. For a proper heat pump setup say at T30, one would need 2.4x. So it is hard to know where the sweet spot is.

 

[Knappers]

I am planning on using cast iron rads, which are not cheap. So at T40 I would need 1.6x the wattage. For a proper heat pump setup say at T30, one would need 2.4x. So it is hard to know where the sweet spot is.

Would have 1.6x, would need 2.4x?

 

[siricosm]

As I understand it, if I calculate rad sized based on T50 rads (70C flow), I would need to multiply the wattage I need by 1.6 to have a 60C flow (T40), or by 2.4 to have a 50C flow (T30).

 

[Knappers]

And by wattage needed you mean equivalent output of rad at T50?

 

[siricosm]

Yes. At T40 the rads would need to be 1.6 times bigger, or 2.4 times bigger at T30. (I think).

 

[Knappers]

More than 1.6 seems excessive practically especially with cast rads.
You'd probably have the only cast iron heat pump system in the country!

 

[siricosm]

You'd probably have the only cast iron heat pump system in the country!

Haha, that could be true, but I really like them, I think they look so much better than the modern ones.

 

[Knappers]

Regarding efficiency.
If you can keep the return temp below dewpoint (52°C i believe) then in theory you'll always be condensing so more efficient.
How likely is it that you'd move to a heatpump in future?
If very likely, I'd look at building in redundancy elsewhere (perimeter heating, ventilation etc)
Have you got another more detailed thread on the project?

 

[siricosm]

Regarding efficiency.
If you can keep the return temp below dewpoint (52°C i believe) then in theory you'll always be condensing so more efficient.
How likely is it that you'd move to a heatpump in future?
If very likely, I'd look at building in redundancy elsewhere (perimeter heating, ventilation etc)
Have you got another more detailed thread on the project?

So for max efficiency, T40 (60C flow) is probably good enough most of the time.

I am redoing the heating in my house in copper pipe with cast iron rads, and then I am going to lay hardwood floors, so I am hoping the system will last until I croak. However before that happens (the croaking part), I am worried that the government is going to ban gas boilers, as they are already talking about it for new builds. And you know how this goes, first it is new builds, and then a few years later people have to do it when their boiler dies. So probably not so likely for the heatpump.

I did have a couple threads about aspects of the system I plan to install, but it was mostly about thermal stores (sealed), and the pros/cons compared to unvented systems.

 

[Knappers]

Yea 60 is a good design temp.
Gas boilers won't get banned for decades and by the time they do heatpumps may not even be a thing.
I've done some work for these guys, down the road from me, a bit special and probably silly money.

Cast iron radiators from the Beaumont range

Beaumont Cast Iron home page offering wide range of exclusive cast iron radiators and accessories

www.beaumontcastiron.com

 

[siricosm]

My favorite are these (our house is 1930s):
Deco Cast Iron Radiator - https://www.tradscastironradiators.co.uk/radiators/cast-iron-radiators/deco/

but I can't afford them, nor the ones in my profile pic. I was originally going to scrounge around for used ones, but then I found these ones which are pretty reasonable:
Traditional Victorian 4 Column 760mm Cast Iron Radiator - https://www.castironradiatorcentre.co.uk/products.asp?code=CDC-760&name=traditional-victorian-4-column-760mm-cast-iron-radiator

 

[siricosm]

Have you got another more detailed thread on the project?

Here you go, I found it:

Please criticize my plan

I am new to the UK and just bought a house in Norwich. It has a vented cylinder and vented CH that is suffering from pretty severe corrosion, some of the rads are rusted through, so I would like to replace it with a sealed system. The rads are all plumbed in 10mm, so I would like to replace that...

www.plumbersforums.net

I guess a lot of folks don't like thermal stores, so it a bit devolved into a discussion of pro/cons with unvented. The plan is to ditch the house thermostat, and have the rads controlled entirely by TRVs. This design should also lower the return temperature a bit on all but the coldests days.

If you have any comments on that thread, or any tips or advice, please feel free to post them there. I am about 1/2 way through the install.

 

[Harvest Fields]

Things have moved where 15 years ago heat only boiler was standard ish now not many are getting installed compared to combis

Tell me about it. I’m tired of seeing combi’s in large 4 bed double bathroom houses.

 

[Knappers]

I've had a look, wouldn't a gledhill boilermate do the job?
I don't love it in principle as I dont think the boiler would be as efficient as id like, that would be overcome by having multiple heat sources (back boiler, solar etc) which is where a thermal store would excel domestically.
Just off the top of my head I'd look at separating heat and hw, something like thermal store temp controlled by weather compensator and HW straight off combi.
Wire solar panel to immersion and I'm there!

 

[siricosm]

Hee-hee, I am a bit farther along then that. I wound up going for a 300l Telford stainless buffer store, which was really inexpensive, and it came with a 3Kw backup immersion, dual stat and TPRV.

I purchased a 165Kw Nordic-tec plate exchanger, so time will tell how high the store temperature needs to be to get decent hot water, I am hoping that 65C will do it. The use of the thermal balancing valve and a smart pump instead of the usual flow switch on the primary side of the DHW exchanger is an experiment, but if it works it would have some advantages.

I would love to put a solar panel on roof and connect it to the immersion, although I should probably update my old boiler first.

 

[Ric2013]

I purchased a 165Kw Nordic-tec plate exchanger, so time will tell how high the store temperature needs to be to get decent hot water, I am hoping that 65C will do it.

I'd be really interested to know how you get on as I've been toying with the idea of a thermal store for myself for some years but am aware that manufacturers often aren't able to give this level of information. Most people run hotter than this as they don't understand the efficiency issue so I doubt it often comes up, but it'd be interesting to know what happens when you actually start pushing the technical limits. Please keep us updated.

 

[king of pipes]

Tell me about it. I’m tired of seeing combi’s in large 4 bed double bathroom houses.

I was the same way of thinking as you H but having recently removed a thermal store unit and fitted my first Viessman 222- f 35kw I would have no issues fitting this product again in a large home ,built in wi-fi , weather compensation tunes the boiler to the optimum energy output what ever the weather outside the digital interface feeds a wealth of information to the LCD screen or via the vicare app to your phone or tablet it just a joy to use and takes all the if what's and maybes out of heating design it's all done in one package and can be tuned and installed in various configurations to suit the property. Thermal stores have there place but they are old technology now in my opinion. Regards Kop

 

[siricosm]

I'd be really interested to know how you get on as I've been toying with the idea of a thermal store for myself for some years but am aware that manufacturers often aren't able to give this level of information. Most people run hotter than this as they don't understand the efficiency issue so I doubt it often comes up, but it'd be interesting to know what happens when you actually start pushing the technical limits. Please keep us updated.

I have it mostly installed and I am just waiting for the heating season to end, and then I will switch it over. However, it will be while after that until I know how well the hot water performs in the winter, and what temperature I need to keep the cylinder.

I should know right away if using a balancing valve on the primary side of the plate exchanger instead of a flow switch on the secondary is a good idea. I have to think the manufacturers of pre-made stores would do that if it worked well, but I don't see why it shouldn't work.

 

[siricosm]

I just thought I would provide an update for anyone interested in the DIY thermal store option.

Here are the parts I purchased for the store:
£430 300l standard Telford buffer, comes with dual stat, TPRV, and a 3kW electric immersion
£145 Nordic Tec Ba-23-40 165kW plate exchanger with insulation
£52 FS-05 flow switch 22mm compression
-------
£627

The 165kW plate exchanger works well with the tank stat set to 60C, at least it works fine now, we will see when it gets colder and the incoming water temperature drops and the heating is on. We don't have such a great flow rate at out place, maybe 10-12l/m, but the shower is alright, much better than the electric shower we had before, and no longer menopausal.

The Rm Cylinders thermostat that came with the Telford tank has a max setting of 65C, but our Ideal FF360 has a max temp of 82C, so I doubt it could go much higher than that anyway without the boiler cycling towards the end. Currently the boiler heats the tank in a single cycle. And it takes a while, the Rm Cylinders dual stat has a large differential, which is nice.

The tank is stainless, and has two 22mm connections at the top and two at the bottom, two stat pockets at the bottom, a TPRV and a spot for an immersion heater. It would have been nice to be able to fit a top and bottom thermometer, and to have one or two connections half way up. Other than that, it seems pretty nice, and is reasonably well insulated, with a modern looking white cover.

Here is the final plan:

 

[John.g]

Very nice schematic of your system must look at it in more detail later but just re the 165kw Hx, what output do you reckon you might/are getting with your flow rate of 10/12 LPM and assuming the cold water temp at 18C (here, just now). Also, be grateful for any info on the design conditions required to give its rated output of 165kw, Amazon state its less than 1 M2 (0.92) of heating surface so seems a hell of a output based on that.

 

[Ric2013]

Thanks so much for the update!

I'm interested as to why you are blending down the DHW to 48°C. It makes sense for effciency but would seem to contravene the requirement for 50°C at the outlets within 30 seconds. That said, as you aren't storing the water then it's effectively like a combi boiler (on which the water regulations blue book makes the 50/30 claim and then says that a combi boiler probably won't comply and then shrugs and wanders off).

So you're getting 10-12 lpm at 48°C with 18°C incoming cold (assumed)? How quickly does that water reach the taps out of interest (I genuinely DESPISE waiting for hot water to run and have got it down to 10-15 seconds in my own house).

 

[siricosm]

Very nice schematic of your system must look at it in more detail later but just re the 165kw Hx, what output do you reckon you might/are getting with your flow rate of 10/12 LPM and assuming the cold water temp at 18C (here, just now). Also, be grateful for any info on the design conditions required to give its rated output of 165kw, Amazon state its less than 1 M2 (0.92) of heating surface so seems a hell of a output based on that.

Thanks. I think the rating is for a 40C difference in temperature across the entire hot to cold side, so I guess it is a maximum rating in ideal conditions with sufficient flow rates. At 10l/m I don't need anything near that. I was also wondering how they get such a large transfer with such a small area, but in the end I took their word for it, and it is a lot larger than a plate exchanger from a combi.

I wanted it to be considerably oversized so that I could run the tank at a lower temperature. I will have to see how low it can go in the middle of winter. I could not really find any definitive answers on the internet, which is a bit surprising. I would have thought that today with heat pumps and buffers a lot of people would be interested in how big a plate exchanger you need if your tank is 55C and you want 12l/m.

 

[siricosm]

Thanks so much for the update!

I'm interested as to why you are blending down the DHW to 48°C. It makes sense for effciency but would seem to contravene the requirement for 50°C at the outlets within 30 seconds. That said, as you aren't storing the water then it's effectively like a combi boiler (on which the water regulations blue book makes the 50/30 claim and then says that a combi boiler probably won't comply and then shrugs and wanders off).

So you're getting 10-12 lpm at 48°C with 18°C incoming cold (assumed)? How quickly does that water reach the taps out of interest (I genuinely DESPISE waiting for hot water to run and have got it down to 10-15 seconds in my own house).

I think it is a legal requirement here that it needs to be max 48C, and the TMV I bought seems to have that as a maximum. I think the idea is to avoid scalding mostly.

The speed depends on the proximity I suppose. The kitchen, laundry and shower are close, but the bath is far away, so it takes some time to get there. Plus the house used to have a vented cylinder, so there is some 22mm pipe still in the hot line for the bath that I need to swap for 15mm when we renovate the bathroom, as that will slow things down.

 

[John.g]

Thanks. I think the rating is for a 40C difference in temperature across the entire hot to cold side, so I guess it is a maximum rating in ideal conditions with sufficient flow rates. At 10l/m I don't need anything near that. I was also wondering how they get such a large transfer with such a small area, but in the end I took their word for it, and it is a lot larger than a plate exchanger from a combi.

I wanted it to be considerably oversized so that I could run the tank at a lower temperature. I will have to see how low it can go in the middle of winter. I could not really find any definitive answers on the internet, which is a bit surprising. I would have thought that today with heat pumps and buffers a lot of people would be interested in how big a plate exchanger you need if your tank is 55C and you want 12l/m.

Its a long long time since my experiences with heat exchangers and LMTDs and all that jazz but one big advantage you have is that you can increase the primary flow rate as its pumped to compensate for lower temperatures but you may already have it running on full speed?, I know you have no temperature gauge on the Hx primary return but it should be pretty cool to the touch IMO for the ~ 23kw you are extracting from it now.

 

[Ric2013]

I think it is a legal requirement here that it needs to be max 48C, and the TMV I bought seems to have that as a maximum. I think the idea is to avoid scalding mostly.

The speed depends on the proximity I suppose. The kitchen, laundry and shower are close, but the bath is far away, so it takes some time to get there. Plus the house used to have a vented cylinder, so there is some 22mm pipe still in the hot line for the bath that I need to swap for 15mm when we renovate the bathroom, as that will slow things down.

This is something I struggled to get my head around. Because there is a legal requirement for scalding protection at outlets (in new bathrooms) and then a legal requirement for legionalla protection.

The understanding I have reached is that the compromise is that the hot water pipe would be heated to 50°C and then mixed down to temperature as close to the terminal fitting (tap) as possible, but that this does not really apply to installations where water is heated at the time of use.

What I meant about speed is, I suppose, how quickly is the pipe directly after the TMV likely to become obviously warm? I'm assuming there must be some lag as the pump kicks in and warms the plate heat exchanger, but it may be only 5 seconds?

 

[siricosm]

Its a long long time since my experiences with heat exchangers and LMTDs and all that jazz but one big advantage you have is that you can increase the primary flow rate as its pumped to compensate for lower temperatures but you may already have it running on full speed?, I know you have no temperature gauge on the Hx primary return but it should be pretty cool to the touch IMO for the ~ 23kw you are extracting from it now.

I am not sure what the flow rate is on the primary side. It is 22mm direct to/from the tank, and has a Grundfos Alpha 2L 15/60. It is set on the middle fixed speed (II), although it also seems to do alright on the lowest fixed speed (I) with current conditions. Again, this is something I can test in winter when the incoming water is colder, as maybe it will need to be increased.

 

[siricosm]

This is something I struggled to get my head around. Because there is a legal requirement for scalding protection at outlets (in new bathrooms) and then a legal requirement for legionalla protection.

The understanding I have reached is that the compromise is that the hot water pipe would be heated to 50°C and then mixed down to temperature as close to the terminal fitting (tap) as possible, but that this does not really apply to installations where water is heated at the time of use.

What I meant about speed is, I suppose, how quickly is the pipe directly after the TMV likely to become obviously warm? I'm assuming there must be some lag as the pump kicks in and warms the plate heat exchanger, but it may be only 5 seconds?

I could be wrong on this, but my understanding was that legionella was only a problem if you had a lot of heated water sitting around, like in a normal vented/unvented cylinder. I thought it was not a worry with combis or a thermal store with a coil or PHE. The idea being that with such a small volume of hot water, the new (chlorinated) water pushes out all the old when it is used.

For the speed, I can measure that and report back. I will wait until no one has used hot water for a while, and then time it.

 

[John.g]

I am not sure what the flow rate is on the primary side. It is 22mm direct to/from the tank, and has a Grundfos Alpha 2L 15/60. It is set on the middle fixed speed (II), although it also seems to do alright on the lowest fixed speed (I) with current conditions. Again, this is something I can test in winter when the incoming water is colder, as maybe it will need to be increased.

By very bacic calcs, you should IMO be able to drop the boiler flow temp to < 55C and still get your 10/12 LPM at 48C, you may be heating ~ 8 LPM to 58C which is mixing with 4 LPM of 18C cold water to give that 10/12 LPM. All you have to do is keep lowering the boiler SP temp, this means the TMV will keep throttling in until fully closed and the "mixed" temp will then start falling below 48C., then just increase the SP temp by a few degrees and you will be opertaing the boiler at its maximum efficiency. Even if my calcs are wrong, it would still be interesting to see how much you can reduce (if any) the SP temp until the TMV is shut.

Obviously, reduce the tank stat setting first and then the boiler SP.

 

[Ric2013]

I could be wrong on this, but my understanding was that legionella was only a problem if you had a lot of heated water sitting around, like in a normal vented/unvented cylinder. I thought it was not a worry with combis or a thermal store with a coil or PHE. The idea being that with such a small volume of hot water, the new (chlorinated) water pushes out all the old when it is used.

For the speed, I can measure that and report back. I will wait until no one has used hot water for a while, and then time it.

That's my understanding too. As I said, does not really apply to water that is heated on demand. Actually, I'm starting suspect some of our laws are, shall we say, manufacturer driven anyway.

Looking forward to your speed test, and again, thank you.