DIY Hydronic pumps, valves, heat exchangers

freds · December 01, 2019, 10:48:15 AM

Also, I have seen the cost quoted for Webasto style pumps which is used in a lot of RV hydronic system in about the $2-300.00 range; with used ones for $100.00 plus, so I have been looking at alternatives.

In sizing pumps does anyone know what the typical flow rates for the pumps should be?

Any suggested tactics for power source 12v for cost, 24v for preheating or depend on house inverter and run 120v ac pumps?

Thanks

luvrbus · December 01, 2019, 11:29:02 AM

Flow rate is based 1gpm for ea 11,000 btu AquaHot told me ,check out the 12 volt solar pumps they are cheap and some might flow 4+gpm

richard5933 · December 01, 2019, 12:52:55 PM

Ours had the main Webasto pump as well as a secondary pump. The secondary pump was a Bosch electric coolant pump.

All were 12v. If you run 120v pumps you're losing efficiency and going to use more battery capacity. Can't see a good reason not to stick with 12vdc pumps.

luvrbus · December 01, 2019, 02:35:39 PM

The system has to have a pump for each zone or engine .the main circulating pump is to circulate the coolant for the Webasto it is not much good for the heat exchangers

freds · December 01, 2019, 04:15:17 PM

Quote from: luvrbus on December 01, 2019, 11:29:02 AM
Flow rate is based 1gpm for ea 11,000 btu AquaHot told me ,check out the 12 volt solar pumps they are cheap and some might flow 4+gpm

Thanks that's a great piece of tribal knowledge!!!!

That also answers my 1/2 PEX (1.2 min/2.3 max GPM) verses 3/4 PEX (2.3/4.6) question that I had in an earlier post. The following link is where I found that info:

http://s3.supplyhouse.com/product_category_files/11448-Flow-Rate-Chart.pdf

freds · December 01, 2019, 06:56:17 PM

Most RV and boats with engine heat recovery for water heating has the following layout:

For preheating and thermosiphon heat recovery I am thinking the following:

However wondering if I should add a check valve to prevent back flow though the pump?

buswarrior · December 02, 2019, 06:36:06 AM

You have created an engine overheating feedback loop.

Front flow will be your issue, not back flow.

If engine pre-heating, why wouldn't you want the heat going thru the heat exchangers?

We're preheating an engine here, it doesn't take much...you works just fine making the trip through the heat exchangers first.

Happy coaching!
Buswarrior

freds · December 02, 2019, 08:41:36 AM

Quote from: buswarrior on December 02, 2019, 06:36:06 AM
You have created an engine overheating feedback loop.

Front flow will be your issue, not back flow.

If engine pre-heating, why wouldn't you want the heat going thru the heat exchangers?

We're preheating an engine here, it doesn't take much...you works just fine making the trip through the heat exchangers first.

Happy coaching!
Buswarrior

OK not sure I understand why this would create an engine over heat situation.

The preheat scenario assumes you have a nice toasty cabin with hot liquid in water heater or hydronic storage tank and you need to pump warmed coolant through the engine to warm it up.

Some bus's have an additional inline pump to assist with heater circuit coolant flow to the front; so that there is an additional pump in the circuit.

I think I have such a pump in my bus so maybe for preheat I wouldn't have to add a pump, simply turn this secondary pump on to circulate engine coolant through the heat storage tank.

My concern for adding the pump as I did in the design was that unless it was energized; it would prevent flow.

So if the bus doesn't have the additional pump, it should be added inline and energized when driver heat is desired?

PS. I wasn't trying to show the entire system; just the engine loop portion as a starting point to a hydronic design with fully isolated loops.

buswarrior · December 02, 2019, 09:31:52 AM

Engine running, the hot coolant will go through your pre-heat pump and back to the cold side of the engine, but still be hot.

Heat exchangers present resistance, the short cut thru the pump will be easier.

There was no where for the coolant to shed its heat.

Engine temps rise, as the coolant entering is already hot.

The same mistake happens with uncontrolled hot water heating loops. Once the hot water tank has reached operating temperature, the coolant returns to the engine hot, again, having no where to shed its heat.

Self-inflicted wound is right up there with Treason...

Nobody gets on these boards and brags they ruined their engine by bypassing the radiator with their home brewed Hydronics...

Unbalanced reporting...

Sometimes "free" is far from it...

Happy coaching!
Buswarrior

sledhead · December 02, 2019, 11:13:21 AM

Most hydronic pumps are a flow through design so no resistance ( or very little ) when the pump is off and you are driving down the road the heat from the engine can some what heat the coach if set up right . Then turn on the pump to pre heat the engine from the coach side heating source to heat the engine b 4 starting a cold engine .

dave

buswarrior · December 02, 2019, 12:15:35 PM

What we need is a proper pump catalogue, with all the specs, sizes of inlet/outlet, flow, pressure, power consumption, so we can make some informed choices.

Can't do good design without good info.

Happy coaching!
Buswarrior

Jim Eh. · December 02, 2019, 12:43:14 PM

Wouldn't 2 heater control valves work. One to control (stop) flow to the heater core and the other to control (stop) flow to the hot water tank? The control to the hot water tank could be thermostatically controlled to "close" at a pre set temperature so as to NOT dump hot water into the radiator(s) cold (cooled) water return curcuit.

buswarrior · December 02, 2019, 12:51:43 PM

Yes, and same as MCI, put them in the return line.

Cooler for longevity.

Happy coaching!
Buswarrior

freds · December 02, 2019, 04:41:40 PM

Thanks guys, great feedback, wondering if the heat exchange for the water heater or hydronic storage should be down stream of the drivers heater core or upstream?

I guess I will have to measure the next time I fire the bus up (it's in a storage yard).

Jim Blackwood · December 03, 2019, 09:21:34 AM

I don't see your preheat source in those drawings. Is it the water heater? That might not be enough.

On my DL the big solenoid is on the supply side and there's a manual valve on the return. This will eventually be changed up a bit but there are many options. As it stands though the interior heat controller shuts down flow once the cabin gets warm enough, which takes care of the bypass problem. Since the webasto is now switched on by the cabin thermostat, a reduction in engine heat which results in cabin cooling will cause the webasto to be fired off, providing more engine heat as well. Not sure if that is going to work well enough to keep the engine temp up so it will take some testing, but there might be a preset temp switch that controls that, I'll have to look.

But none of that is a problem, the issue is with excluding engine heat when parked. Currently a very inefficient system that will eventually be changed. In any case, all these pumps are centrifugal type. None are positive displacement. So all will backflow when unpowered. Only way to deal with that is with a valve or a check, and checks reduce flow.

To design a system that does everything you want it is often best to start with an all inclusive list of everything that you want, and use that to figure out how to get from here to there. But like electrical wiring you have to be mindful of your returns and recognize that water goes where it can go, not just where you want it. When those pumps don't run they may as well be straight pipes.

Jim