Jump to content

How to connect a central heating system with multiple heat sources


Featured Posts

I have three heat sources all in the stern of my boat:

 

  • My keel cooled Beta 38 engine
  • An eberspacher D4WSC hydronic rated at 4.3kW
  • A 4.2kW Villager Puffin stove with a back boiler (something like this)

 

 

These heat sources need to drive:
 

  • A twin coil calorifier
  • 3x or 4x radiators (which I still need to buy).

 

At the moment only the engine is plumbed into the calorifier. The eber used to drive two rads which I removed due to leaking, the pipes are still in place but I need to add at least one more rad to them. My neighbour plumbed his engine circuit into his rads so the engine heats the boat which seems like a great idea! First prize would be if I could use all three sources for heating the boat but I read this topic and the Eber pump might be a problem, though it is on an open vented system.

 

What's the best way to connect this system?

 

I'm thinking of using 3x 1362W rads and 1x 401W towel rail which makes 4487W. I have heard it is better to drive the Eber hard and if I did connect the back boiler I think that it would do well to suck out more heat from my Puffin which is in a rather small room. Is this too much to expect my system to drive?

Edited by jetzi
Link to post
Share on other sites

I put in a heat store with the calorifier above it, the engine heated it, the Rayburn heated it and lastly the whispergen heated it. The calorifier was a single coil and was heated by gravity, the central heating was pumped out of the heat store, simples. 

Link to post
Share on other sites

Nearly anything will drive the system but it's the temperature the system will reach from each heat source that will be different.  I suspect the stove my run the system cooler than the engine and the engine cooler than the Eber.

 

The stove means that unless you are a total digit intent one steam explosions the heating system needs to be open vented with a header tank. The engine will normally run a pressurised cooling system so can't be connected to an open vent system. The answer is to use a heat exchanger in the return from the calorifier to engine to heat the radiator water. This will demand a pumped system but Eber pump may well suffice if you can run it on its own.

 

The stove will ideally use large bore pipes and gravity circulation so the hotter the stove gets the faster the water circulates and dumps heat. You can feed Eber heated water through a gravity system but it may need valves to prevent Eber water short-circuiting through the stove (depending upon how everything is piped). If you pump the stove then pump failure is very likely to end up with steam and rusty water spray blowing out of the header tank.

 

 

 

 

 

Link to post
Share on other sites
21 minutes ago, Tony Brooks said:

The answer is to use a heat exchanger in the return from the calorifier to engine to heat the radiator water.

 

This sounds great! So I have two circuits connected by a heat exchanger, one with the engine and one cauli coil, and another that has the eber, stove, cauli, and rads all in parallel?

Link to post
Share on other sites

We have central heating run by a Mikuni, much the same as an Eber. The Mikuni hot outlet is Teed, one branch goes to the radiators, the other to the second coil in the Calorifier.

I added a plate heat exchanger which is in the engine skin tank loop (so as to avoid any possibility of over-cooling the engine) and a small pump. Low operating pressure 1-way valves (or could be flap valves) mean that hot water from the engine heat exchanger pump can’t back flow into the Mikuni, and ditto the Mikuni can’t pump water back through the heat exchanger.

 

Getting “free” heat to the radiators when we are cruising, gives me a “warm feeling” in more ways than one!

 

In theory you could add a third source ie another pump pushing hot water from a back boiler into the same circuit with a third 1-way valve to prevent back-flow, but as Tony mentions, in practice this is risky because you have to consider what happens if the pump or electricity supply fails with the stove lit.

Edited by nicknorman
Link to post
Share on other sites
15 minutes ago, nicknorman said:

I added a plate heat exchanger which is in the engine skin tank loop (so as to avoid any possibility of over-cooling the engine)

Why does it matter which loop it's in? Either way it's taking the same amount of heat out?

 

I also love the idea of free heat from the engine, especially because I run my engine so much more in winter. The install cost is not small though, I found a 0-7kW plate heat exchanger here for 150 GBP: https://www.stovesonline.co.uk/wood_burning_stoves/Plate-Heat-Exchangers.html

 

20 minutes ago, nicknorman said:

in practice this is risky because you have to consider what happens if the pump or electricity supply fails with the stove lit.

To be honest I'm leaning towards not installing the back boiler, seems like too much of a risk. My main reason for it though is to spread the heat from the stove which is in a smallish room. But I also like having the redundancy of multiple ways to heat.

Link to post
Share on other sites

The have an Alde boiler that heats radiators, and hot water with a coil in the calorifier.  In addition there is a second coil in the calorifier connected to the engine cooling.  To get free heat in the boat whilst cruising we simply turn on the Alde circulation pump and it basically uses the calorifier as a heat exchanger to transfer heat from the engine cooling to the radiators.
 

Works quite well for a no cost option, but don’t forget to turn the circulation pump off when you stop or you will have no hot water in 30 mins!.

  • Greenie 1
Link to post
Share on other sites
2 minutes ago, john6767 said:

To get free heat in the boat whilst cruising we simply turn on the Alde circulation pump and it basically uses the calorifier as a heat exchanger to transfer heat from the engine cooling to the radiators.

Wow, does this work? Essentially turning the Calorifier into a thermal store like @peterboat suggested! Does this mean the calorifier circuit needs to be in series with the radiators, otherwise wouldn't it just circulate through the alde?

 

I am not sure if I can turn the circulation on the Eber on without the Eber being on, but it's worth tinkering with to find out. Thanks, great suggestion, I think I will experiment with this rather than trying to buy a heat exchanger and mess with the engine cooling.

 

 

Link to post
Share on other sites
19 minutes ago, jetzi said:

Why does it matter which loop it's in? Either way it's taking the same amount of heat out?

 

The calorifier loop is usually before the thermostat so "steals" heat from the engine and can cool it too much in some conditions.  The skin tank loop is after the thermostat so is all waste heat - it's heading off to the skin tank to be cooled, so using this to heat the boat has no effect on the engine temperature.

  • Greenie 2
Link to post
Share on other sites
30 minutes ago, jetzi said:

Wow, does this work? Essentially turning the Calorifier into a thermal store like @peterboat suggested! Does this mean the calorifier circuit needs to be in series with the radiators, otherwise wouldn't it just circulate through the alde?

 

I am not sure if I can turn the circulation on the Eber on without the Eber being on, but it's worth tinkering with to find out. Thanks, great suggestion, I think I will experiment with this rather than trying to buy a heat exchanger and mess with the engine cooling.

 

 

It certainly does work.  OK the radiators are not as hot as when the boiler is heating them, but it warms the boat up fine.  As I mentioned you soon end up with a calorifier full of tepid water if you forget to turn the pump off when you stop, so that is an indication of how much heat it is taking out of the system.  It has the other advantage of providing additional engine cooling if you are going to be caning the engine, eg on the Ribble link.

 

I assume the rads and the calorifier coil are in series as the boiler always heats the water, there are some valves under the bed where the calorifier is which I suspect allow you to bypass the coil if you want to, but as the valves are not easily accessible and it does what we want I have never played with them.

 

Edited to add; the pump on our system is controlled by the central heating thermostat, so you need to be certain that is set high so the the heating thinks I needs to run, eg turn it right the way up!

Edited by john6767
Link to post
Share on other sites
53 minutes ago, jetzi said:

Why does it matter which loop it's in? Either way it's taking the same amount of heat out?

 

I also love the idea of free heat from the engine, especially because I run my engine so much more in winter. The install cost is not small though, I found a 0-7kW plate heat exchanger here for 150 GBP: https://www.stovesonline.co.uk/wood_burning_stoves/Plate-Heat-Exchangers.html

 

To be honest I'm leaning towards not installing the back boiler, seems like too much of a risk. My main reason for it though is to spread the heat from the stove which is in a smallish room. But I also like having the redundancy of multiple ways to heat.

I think I paid about £50 for the plate heat exchanger. There are a lot of them about, eg on eBay, but it is important to work out how you are going to connect it. Lots of them are designed to be push-fit into a boiler casting sealed by O rings etc. I would want one with threaded spigots so eg a tap connector can be used. A quick perusal of of eBay gives this one: https://www.ebay.co.uk/itm/Ravenheat-DHW-Plate-Heat-Exchanger-0002SCA06015-0-0002SCA06015-1-Genuine-NEW/262152319632?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20201210111314%26meid%3Db074f9cf39a9477c903c1fb222159c84%26pid%3D101195%26rk%3D4%26rkt%3D12%26mehot%3Dco%26sd%3D233481976988%26itm%3D262152319632%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWebWithDarwoV3BBEV2b%26brand%3DRavenheat&_trksid=p2047675.c101195.m1851

 

which seems to have threaded stubs, probably 3/4” and 1/2” BSP but you’d need to check with the seller.

 

Just a word on the thermal rating of plate heat exchangers, heat only flows from one side to the other in proportion to temperature difference. Or to put it the other way, the more the heat flow, the more the output temperature is less than the input. Since with a boats cooling system you may only be starting with 75deg, you don’t want to drop much temperature and so the rating of the plate heat exchanger needs to be much more than you might think. Not because that much heat is going to flow, but because you want to minimise temperature drop. I slightly under-rated my exchanger so the rads get hot, but not as hot as I’d have liked.

 

FYI I used this small pump which so far is pretty good (about 7 years use or so, but only as a leisure user). They are cheap so I bought 2, spare one is still sitting in a box somewhere!

 

https://solarproject.co.uk/phoenix1/product_info.php?products_id=24&ceid=77d16f3e4d1fdbcaa50f4dc0e85257ec

 

 

Edited by nicknorman
  • Greenie 1
Link to post
Share on other sites
1 hour ago, jetzi said:

Wow, does this work? Essentially turning the Calorifier into a thermal store like @peterboat suggested! Does this mean the calorifier circuit needs to be in series with the radiators, otherwise wouldn't it just circulate through the alde?

 

I am not sure if I can turn the circulation on the Eber on without the Eber being on, but it's worth tinkering with to find out. Thanks, great suggestion, I think I will experiment with this rather than trying to buy a heat exchanger and mess with the engine cooling.

 

 

I have a thermal store below the calorifier its a separate thing, I set it up 7 or 8 years ago its simple and works well, it also allows the rads to run for a while after the engine has stopped. The other thing is in summer it reheats the calorifier for about 24 hours after the engine has stopped as well.

Link to post
Share on other sites
1 hour ago, TheBiscuits said:

 

Can you remember what size you used Nick?

In terms of its ratings might have been 24kw, but as I said earlier that is meaningless unless you also specify the temperature drop. But here is a photo, you can see it doesn’t have many plates.


EEB7F5A6-30A8-4DE8-9E71-6461B6A5052F.jpeg.c85da087347e0e8c28d467bc4e63c0ef.jpeg
 

You can also perhaps see that the skin tank side is “short circuited” by that gate valve. The worry was that the exchanger might have impeded coolant flow to the skin tank, and so that gate valve could be opened to bypass the exchanger. However I’ve never needed to do that, including prolonged high rpm work on the tidal Trent and tidal Yorkshire Ouse. 

Edited by nicknorman
  • Greenie 2
Link to post
Share on other sites

I have a webasto and engine heating going to the calorifier and rads it works very well except with long periods of tickover and lock flights (same thing really) the engine can become overcooled as it doesn't generate 4-5 kilowatts of heat so gradually the temperature drops. If you are just charging the engine will never reach 80 degrees or above only when cruising at canal speed. I have a seperate pump for the plate heat exchanger (foam insulated from Germany via EBay) which I can switch off for the long tickover times. The inbuilt engine thermostat opens at 75 degrees but only shuts somewhere below 60 which is way to cold to run an engine. The Rads in the boat will get hotter from the engine 85C the webasto gives 65C degrees to the rads

Link to post
Share on other sites
21 hours ago, jetzi said:

Why does it matter which loop it's in? Either way it's taking the same amount of heat out?

 

I also love the idea of free heat from the engine, especially because I run my engine so much more in winter. The install cost is not small though, I found a 0-7kW plate heat exchanger here for 150 GBP: https://www.stovesonline.co.uk/wood_burning_stoves/Plate-Heat-Exchangers.html

 

To be honest I'm leaning towards not installing the back boiler, seems like too much of a risk. My main reason for it though is to spread the heat from the stove which is in a smallish room. But I also like having the redundancy of multiple ways to heat.

Have a look at this.

.https://www.ebay.co.uk/itm/Stainless-steel-PLATE-HEAT-EXCHANGER-NORDIC-TEC-25-65kW-INSULATION-BOX-HQ/233481969648?hash=item365c9c1ff0:g:~tIAAOSwSA5eNIvJ

Similar to the one I have, which works well.

 

Bod

Link to post
Share on other sites
21 minutes ago, Bod said:

Yes that looks a much better “fatness” apart from the 25kw one. Probably the 45kw one would be fine, although if space isn’t an issue, the 65kw one is not much more. 

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.