Plate heat exchanger to heat radiators from engine.

[JoshS]

Hi! I'll soon be needing to replace the hoses between my engine (Isuzu 4LB 33) and skin tank, and was thinking about adding a plate heat exchanger to see if I can get a bit of heat to the radiators when cruising in winter. I know a few people on here have done this, but I'm not sure about a few things. 

 

This is the plate heat exchanger I'm looking at getting: Ebay link, does anyone have any suggestions what size I should get? Also, am I going to have issues finding converters for the 3/4" threads with this? The engine hoses are 35mm and the central heating side is 22mm push fit plastic pipe.

 

I think I will need to add another central heating pump to the radiator circuit as I don't think I can run my eberspacher (HS3 D4E) pump by itself. Would I need to put the heat exchanger and pump in parallel with the eberspacher (with shut off valves to divert?) or can I put it in series, which would mean pumping through the eberspacher with it turned off? 

 

Many thanks for taking a look! 

[Jen-in-Wellies]

3 minutes ago, JoshS said:

Also, am I going to have issues finding converters for the 3/4" threads with this?

Assuming this is 3/4" BSP, then no. In metal, these hose tails are expensive in the larger sizes.

 

7 minutes ago, JoshS said:

The engine hoses are 35mm

Are you sure? More usual sizes are 32mm (1.25") and 38mm (1.5"), though 35mm does exist.

 

11 minutes ago, JoshS said:

This is the plate heat exchanger I'm looking at getting: Ebay link, does anyone have any suggestions what size I should get?

I have no experience of these.

[Tacet]

Tap connectors will be available to fit both heat exchanger and push fit.

 

I put the pump in series with the eberspacher and it circulated fine.  Perhaps best to take the electric feed to the pump off the ignition circuit to prevent leaving it on.

 

It works well.

[magnetman]

The smallest HE in the eBay link seems to be 25kW. Is this not a little on the large size?

 

I did wonder about doing similar using one of those EGR things from a diesel vehicle. They are very nice little heat exchangers.

 

https://www.ebay.co.uk/itm/125649225955?epid=1509788808&hash=item1d414708e3:g:PeoAAOSw541jjlWV&amdata=enc%3AAQAHAAAAoDRE%2Fek8Way4TdJ6twYBEf2GhJ4SM%2Bo7Orj9%2BKFpBw2VLYvsuGIrVn2hHP176yIQeCt%2B6duAuAa%2Bq88NhE3lQB%2FhmuoYaB%2FkdhhqRjmW6hqQPCSX2Q1mwAf13drABjsgm2vnhwXVtVYG19tiugQVIOQN96l308cpgnfxou1awbYgH%2B8M4GHyiz%2Fod0Vikeq%2BIiCcVWw8M8xoMIyeCgKWgKs%3D|tkp%3ABk9SR-bLnomiYQ

 

Tube type heat exchanger (some of them are stainless).

 

[img]https://i.ebayimg.com/images/g/PeoAAOSw541jjlWV/s-l1600.png[/img]

 

 

 

 

Edited December 14, 2022 by magnetman

[JoshS]

7 minutes ago, Jen-in-Wellies said:

Are you sure? More usual sizes are 32mm (1.25") and 38mm (1.5"), though 35mm does exist.

Perhaps! I actually got that information from looking at another thread on here for this engine and just assumed it was a standard size, so clearly more thorough research to be done here! 

8 minutes ago, Tacet said:

Tap connectors will be available to fit both heat exchanger and push fit.

 

I put the pump in series with the eberspacher and it circulated fine.  Perhaps best to take the electric feed to the pump off the ignition circuit to prevent leaving it on.

 

It works well.

Thank for the info about putting it in series, that makes things much more simple! Will definitely switch the pump with the ignition too, cheers! 

 

Do you know what size your heat exchanger is, and how many radiators does it feed? 

[PaulJ]

I use the same make to heat the hot water in my calorifier from the back boiler (failed coil in calorifier) when Im stationary and off shore power.

I use a BA 12-20 45kw which about does it. Its the heat differential /area which makes it work so whereas you wont go too big if you go too small it will take ages.

At a guess I would use at least the next size up.

Other thing you need to consider is that they have small passages in them so some sort of filter to stop blocking it and be prepared to flush it out every now and again unless your systems are immaculate. I just use one of those inline Y filters so I can easily check whats collecting when I remember.

Edited December 14, 2022 by PaulJ

[Bod]

24 minutes ago, JoshS said:

Hi! I'll soon be needing to replace the hoses between my engine (Isuzu 4LB 33) and skin tank, and was thinking about adding a plate heat exchanger to see if I can get a bit of heat to the radiators when cruising in winter. I know a few people on here have done this, but I'm not sure about a few things. 

 

This is the plate heat exchanger I'm looking at getting: Ebay link, does anyone have any suggestions what size I should get? Also, am I going to have issues finding converters for the 3/4" threads with this? The engine hoses are 35mm and the central heating side is 22mm push fit plastic pipe.

 

I think I will need to add another central heating pump to the radiator circuit as I don't think I can run my eberspacher (HS3 D4E) pump by itself. Would I need to put the heat exchanger and pump in parallel with the eberspacher (with shut off valves to divert?) or can I put it in series, which would mean pumping through the eberspacher with it turned off? 

 

Many thanks for taking a look! 

I have done this.

Get the smallest plate exchanger, with insulation.

I found a car electric hot water pump, (Vauxhall Omega from memory I think) this decided the heater hose size, and fitting needed.  A gate valve to control flow, and ball valve to isolate the two sides of the radiator circuit.

Be aware that this will take a lot of heat from the engine, and hot water tank, so will need the flow reducing to the rads, using the gate valve partially open.

I have wired the pump via the start battery isolator, so once the engine is finished with and the isolator switched, the flow stops.

It works well, but you do have to allow the engine to warm up, and the hot water tank to be heated.

 

Bod

[Tracy D'arth]

The 45kw HE will cope, smaller will take for ever to heat the radiators. I know it seems illogical but it really is the minimum size required. 3/4" BSP to 22mm push fit connectors are common in Hep2O and Speedfit etc.

[PaulJ]

12 minutes ago, Bod said:

I have done this.

Get the smallest plate exchanger, with insulation.

I found a car electric hot water pump, (Vauxhall Omega from memory I think) this decided the heater hose size, and fitting needed.  A gate valve to control flow, and ball valve to isolate the two sides of the radiator circuit.

Be aware that this will take a lot of heat from the engine, and hot water tank, so will need the flow reducing to the rads, using the gate valve partially open.

I have wired the pump via the start battery isolator, so once the engine is finished with and the isolator switched, the flow stops.

It works well, but you do have to allow the engine to warm up, and the hot water tank to be heated.

 

Bod

You should try a pipe stat to control it all-works a treat.

[Tacet]

20 minutes ago, JoshS said:

 

Do you know what size your heat exchanger is, and how many radiators does it feed? 

The heat exchanger needs to be rated higher than you would expect as the kW related to a greater temperature difference than will be achieved.  It is a bit of guesswork, but possibly the 35kW would suffice for 3 rads in a 60 ft boat. You may want to go a bit higher to be on the safe side.

 

I put the exchanger in the calorifier circuit which means the plumbing is conveniently located if you have a twin coil system.  In my case, the engine had dual thermostats but if not, the engine should  be up to temperature before turning the pump on.

 

 

 

 

 

 

 

 

 

[TheBiscuits]

24 minutes ago, Bod said:

Be aware that this will take a lot of heat from the engine, and hot water tank, so will need the flow reducing to the rads, using the gate valve partially open.

 

If the heat exchanger is not on the calorifier circuit this won't happen.

 

Put the heat exchanger in the circuit going to the skin tank and you'll only use waste heat for warming up the radiators.

[JoshS]

Yeah I'm aware that I don't want to put it into the calorifier circuit as this may prevent the engine from ever warming up properly, so I'm definitely going to be putting it in the skin tank circuit. I'd also heard that I want to get bigger than I think, so I think the 45kW exchanger is the one I'm going to go for. 

Edited December 14, 2022 by JoshS

[jonesthenuke]

2 hours ago, JoshS said:

Yeah I'm aware that I don't want to put it into the calorifier circuit as this may prevent the engine from ever warming up properly, so I'm definitely going to be putting it in the skin tank circuit. I'd also heard that I want to get bigger than I think, so I think the 45kW exchanger is the one I'm giung to go for. 

 I suggest you need to place the HE in parallel with the skin tank rather in series with it as the small ports out otherwise restrict the flow to the skin tank. Probably not a good thing to find out next time you are cruising a river against the flow. 

 

I have used these for domestic solar water heating projects and they are very good. Add valves to make it easy to isolate and drain etc. Filters (strainers) are a good idea. The comparatively high rating in relation to the radiator load means that some fouling will have limited effect on overall performance. Take care for find pipe fittings where you can have rubber seals acting on the flat ends of the pipe connections as its harder to get a good seal on the threads as they are parallel.

[JoshS]

2 minutes ago, jonesthenuke said:

 I suggest you need to place the HE in parallel with the skin tank rather in series with it as the small ports out otherwise restrict the flow to the skin tank. Probably not a good thing to find out next time you are cruising a river against the flow. 

 

I have used these for domestic solar water heating projects and they are very good. Add valves to make it easy to isolate and drain etc. Filters (strainers) are a good idea. The comparatively high rating in relation to the radiator load means that some fouling will have limited effect on overall performance. Take care for find pipe fittings where you can have rubber seals acting on the flat ends of the pipe connections as its harder to get a good seal on the threads as they are parallel.

Hmm yeah I did wonder if it would be a bad idea to restrict the flow, putting the heat exchanger in parallel is a good idea though and also covers me in case it gets blocked!

 

The pipe fittings are definitely my biggest concern right now, I think I'm going to get the heat exchanger now so I can spend a decent amount of time hunting down the best connectors before I actually put this project together! 

[nicknorman]

9 hours ago, magnetman said:

The smallest HE in the eBay link seems to be 25kW. Is this not a little on the large size?

 

No. It’s on the small size. You have to understand what the kw rating of a heat exchanger means. It means the amount of heat that can be transferred with an unspecified but usually VERY LARGE temperature difference. It might take perhaps 50C temperature difference to transfer 25kw. So if you engine is 70c then your radiators will be 20c. Barely warm. That of course assumes the radiators could dissipate 25kw at 20C, which of course they can’t. Anyway the point is that the larger the kw rating, the less temperature difference between the two sides of the exchanger. Since you are typically starting with 75-80C engine temperature, and CH radiators are designed to run at around 80C, you want the biggest heat exchanger you can reasonably have, in order to keep the temperature difference to a minimum.

 

Heat only flows from hot to cold, and the less “resistance” (= higher kw rating of the exchanger) the less temperature drop is needed to get a certain amount of heat to flow.

[nicknorman]

9 hours ago, JoshS said:

Hi! I'll soon be needing to replace the hoses between my engine (Isuzu 4LB 33) and skin tank, and was thinking about adding a plate heat exchanger to see if I can get a bit of heat to the radiators when cruising in winter. I know a few people on here have done this, but I'm not sure about a few things. 

 

This is the plate heat exchanger I'm looking at getting: Ebay link, does anyone have any suggestions what size I should get? Also, am I going to have issues finding converters for the 3/4" threads with this? The engine hoses are 35mm and the central heating side is 22mm push fit plastic pipe.

 

I think I will need to add another central heating pump to the radiator circuit as I don't think I can run my eberspacher (HS3 D4E) pump by itself. Would I need to put the heat exchanger and pump in parallel with the eberspacher (with shut off valves to divert?) or can I put it in series, which would mean pumping through the eberspacher with it turned off? 

 

Many thanks for taking a look! 

 

I did this. I would go for the 45kw version. When I did it I went for the 25kw version but it isn’t really enough, rads could do with being hotter. Bigger kw rating =hotter radiators.

 

It was a slight faff getting adaptors for the pipe fittings but not that difficult. Sorry, it was several years ago and I can’t remember the detail.

 

As to the plumbing I put them in parallel with low opening pressure non-return valves from Solarproject, such that there was no back-circulation through the diesel heater when the exchanger was in use, and vice versa. No need for manual valves, it was “automatic” in that you just turned on the thing you wanted (diesel heater, or heat exchanger pump) and it worked without any faffing. So I also needed to pump the coolant when the exchanger was in use. I used a pump from solarproject too. https://solarproject.co.uk/phoenix15/index.php?cPath=5  Hmmm, can’t immediately see that they still sell the low opening pressure non-return valve but you could ask them.

 

If you put them in series, you will be heating up the “other one” which will waste heat.

[JoshS]

20 minutes ago, nicknorman said:

 

I did this. I would go for the 45kw version. When I did it I went for the 25kw version but it isn’t really enough, rads could do with being hotter. Bigger kw rating =hotter radiators.

 

It was a slight faff getting adaptors for the pipe fittings but not that difficult. Sorry, it was several years ago and I can’t remember the detail.

 

As to the plumbing I put them in parallel with low opening pressure non-return valves from Solarproject, such that there was no back-circulation through the diesel heater when the exchanger was in use, and vice versa. No need for manual valves, it was “automatic” in that you just turned on the thing you wanted (diesel heater, or heat exchanger pump) and it worked without any faffing. So I also needed to pump the coolant when the exchanger was in use. I used a pump from solarproject too. https://solarproject.co.uk/phoenix15/index.php?cPath=5  Hmmm, can’t immediately see that they still sell the low opening pressure non-return valve but you could ask them.

 

If you put them in series, you will be heating up the “other one” which will waste heat.

Mon return valves seem like a great idea cheers! Will definitely look into that. 

[nicknorman]

4 minutes ago, JoshS said:

Mon return valves seem like a great idea cheers! Will definitely look into that. 

You just have to be a bit careful  - bog standard plumbing non-return valves have a very high opening pressure such that a circulation pump won’t open it. Hence the specialised low opening pressure ones I got. Or maybe look into flap valves (sometimes called swing check valves) which also have low opening pressure. Flap/swing valves have to be mounted in the correct orientation I think.

[David Mack]

5 hours ago, jonesthenuke said:

I suggest you need to place the HE in parallel with the skin tank rather in series with it as the small ports out otherwise restrict the flow to the skin tank.

If you put the HE in series with the skin tank you can potentially use all the waste heat from the engine, but if you put them in parallel the HE will only see a proportion of the flow and hence only a proportion of the available heat.

[jonesthenuke]

42 minutes ago, nicknorman said:

No. It’s on the small size. You have to understand what the kw rating of a heat exchanger means. It means the amount of heat that can be transferred with an unspecified but usually VERY LARGE temperature difference. It might take perhaps 50C temperature difference to transfer 25kw. So if you engine is 70c then your radiators will be 20c.

I am sceptical about this. As well as the solar heating systems that I mentioned in my earlier post I have a similar heat exchanger which interfaces a wood fired range cooker to the central heating system in our house (this avoids interactions between the two systems). I have used this for over ten years. The cooker can provide about 12 kW of water heating. The temperature difference between the two water systems is very small, typically less than 5C (measured with an IR gun). I suggest the OP looks for the design information for the  proposed heat exchanger, or a similarly rated one. Note they should be arranged in contra-flow to get the lowest temperature difference.

 

 

[nicknorman]

5 hours ago, jonesthenuke said:

 I suggest you need to place the HE in parallel with the skin tank rather in series with it as the small ports out otherwise restrict the flow to the skin tank. Probably not a good thing to find out next time you are cruising a river against the flow. 

 

I have used these for domestic solar water heating projects and they are very good. Add valves to make it easy to isolate and drain etc. Filters (strainers) are a good idea. The comparatively high rating in relation to the radiator load means that some fouling will have limited effect on overall performance. Take care for find pipe fittings where you can have rubber seals acting on the flat ends of the pipe connections as its harder to get a good seal on the threads as they are parallel.

I put the HE in series with the skin tank (before it, obviously). I also installed a HE bypass with a gate valve with the same diameter as the skin tank pipe, so if the valve is closed, all the coolant has to route through the HE. If the valve is open, the coolant can bypass the HE and there is no restriction.

 

However in practice I have never had to open the HE bypass and that included Keadby to Torksey (Tidal Trent) at 2200rpm all the way (Beta 43) because the temperature gauge didn’t budge at all from its normal indication of around 75C. And that was with a rather undersized HE. With a larger HE there would be less restriction. So in reality I don’t think it’s an issue.

[JoshS]

3 minutes ago, nicknorman said:

I put the HE in series with the skin tank (before it, obviously). I also installed a HE bypass with a gate valve with the same diameter as the skin tank pipe, so if the valve is closed, all the coolant has to route through the HE. If the valve is open, the coolant can bypass the HE and there is no restriction.

 

However in practice I have never had to open the HE bypass and that included Keadby to Torksey (Tidal Trent) at 2200rpm all the way (Beta 43) because the temperature gauge didn’t budge at all from its normal indication of around 75C. And that was with a rather undersized HE. With a larger HE there would be less restriction. So in reality I don’t think it’s an issue.

I was about to say having a bypass valve might be a better option than having it in parallel with the skin tank, good to hear someone else has implemented that option! 

[jonesthenuke]

Here is some information of a similar heat exchanger (from here https://docs.rs-online.com/f54c/0900766b81610d02.pdf. its just the first that I found)

The exchanger is 172mm by 80 and has 10 plates (the smallest in their range, and similar to the Ebay item)

 

Take the table for potable heating on page 5. Primary side 70C inlet and 50C outlet (engine coolant). Secondary side 10C inlet and 60C outlet. (Note 10C temperature difference between the engine outlet and the heated flow to the radiators.

 

With this arrangement the system can move 6kW, for 20 plates it would 14kW.

 

The temperatures are not exactly what you would have in the proposed system (though engine temperature is close enough and 60C to the rads is OK) but they are close enough to show that these small heat exchangers are in the right ball park. The power rating is adequate, three radiators at 6kW total would heat a boat reasonably well and 14kW would be more than enough.

 

So I suggest a 10 plate would be OK and if you want to go larger for a small increase in cost that would provide a good margin.

 

Note I suspect overall heat transfer will be limited by the flow achieved in both loops rather than the heat exchanger itself, especially as the radiator side flow will be small given the (suspected) use of a 12 V pump?

 

I hope this helps and  I wish you well with this project.

 

[nicknorman]

21 minutes ago, jonesthenuke said:

I am sceptical about this. As well as the solar heating systems that I mentioned in my earlier post I have a similar heat exchanger which interfaces a wood fired range cooker to the central heating system in our house (this avoids interactions between the two systems). I have used this for over ten years. The cooker can provide about 12 kW of water heating. The temperature difference between the two water systems is very small, typically less than 5C (measured with an IR gun). I suggest the OP looks for the design information for the  proposed heat exchanger, or a similarly rated one. Note they should be arranged in contra-flow to get the lowest temperature difference.

 

well I’d agree that the OP should look for the design info, however this seems hard to find. Quoting a kw rating is meaningless unless a temperature difference and circulation speeds are also quoted, and yet PHE manufacturers don’t seem to do that. A 25kw PHE can probably transfer 25kw of heat in a Combi boiler with incoming cold water at 10C and a temperature on the other side of the HE at 70C or the like, but that of course is temperature difference of 60C. I think the important point is that there is no down-side to over-speccing the PHE kw rating, other than cost. Whereas underspeccing it will give rather cool radiators.

[nicknorman]

4 minutes ago, jonesthenuke said:

Here is some information of a similar heat exchanger (from here https://docs.rs-online.com/f54c/0900766b81610d02.pdf. its just the first that I found)

The exchanger is 172mm by 80 and has 10 plates (the smallest in their range, and similar to the Ebay item)

 

Take the table for potable heating on page 5. Primary side 70C inlet and 50C outlet (engine coolant). Secondary side 10C inlet and 60C outlet. (Note 10C temperature difference between the engine outlet and the heated flow to the radiators.

 

With this arrangement the system can move 6kW, for 20 plates it would 14kW.

 

The temperatures are not exactly what you would have in the proposed system (though engine temperature is close enough and 60C to the rads is OK) but they are close enough to show that these small heat exchangers are in the right ball park. The power rating is adequate, three radiators at 6kW total would heat a boat reasonably well and 14kW would be more than enough.

 

So I suggest a 10 plate would be OK and if you want to go larger for a small increase in cost that would provide a good margin.

 

Note I suspect overall heat transfer will be limited by the flow achieved in both loops rather than the heat exchanger itself, especially as the radiator side flow will be small given the (suspected) use of a 12 V pump?

 

I hope this helps and  I wish you well with this project.

 

Useful information. However I think your interpretation is wrong. It is all about temperature difference and in your cited example, the incoming water is at 10C. Big temperature difference compared to primary side, which equals lots of heat transferred! Whereas in a radiator system the returning radiator water should be about 10C less than the outgoing water, ie if the primary side is 70/50 the radiator side would be 60/50 and at that (40C greater return temperature) the heat transfer would be MUCH less so that in reality you would get nowhere near 60C. And really 60C is not particularly hot for a radiator system. The max is 80C and that is what diesel heaters generally give out (well, that is what our Mikuni does anyway). With an engine only at 75C you obviously can’t get 80C but the closer the better, and that is achieved by as big a HE as is reasonably feasible (on grounds of size and cost).