Heat pump project

Hello all, I have an idea for a winter holiday project and I'd welcome any comments or criticisms. I am an engineer but not familiar with heat pump systems, other than the basic principles.

What I'd like to do:
Couple a salvaged car air-conditioner system to a small air-cooled diesel stationary engine that I already have.
The cooling air (and possibly exhaust) from the engine is ducted through the heat exchanger (the alloy radiator from the car), hopefully eliminating the problems of icing and poor COP during cold weather.
The condenser would be replaced with a simple tube-in-tube heat exchanger to transfer heat to a domestic hot water system.

Questions: Will this work at all, or have I made a fundamental mistake? Is there any hope of the performance being reasonable?

What (UK) car has a system that would lend itself well to this application? What about recharging it?

Thanks!

Edit: I meant to say "central heating system". About 5kW worth of heat would be nice - any chance?

Quote:

---

Originally Posted by et0

Hello all, I have an idea for a winter holiday project and I'd welcome any comments or criticisms. I am an engineer but not familiar with heat pump systems, other than the basic principles.

What I'd like to do:
Couple a salvaged car air-conditioner system to a small air-cooled diesel stationary engine that I already have.
The cooling air (and possibly exhaust) from the engine is ducted through the heat exchanger (the alloy radiator from the car), hopefully eliminating the problems of icing and poor COP during cold weather.
The condenser would be replaced with a simple tube-in-tube heat exchanger to transfer heat to a domestic hot water system.

Questions: Will this work at all, or have I made a fundamental mistake? Is there any hope of the performance being reasonable?

What (UK) car has a system that would lend itself well to this application? What about recharging it?

Thanks!

---

In principle yes it would work, but it would not be cost effective.

What you need is a small car engine that can be converted to run on gas (lpg) and then convert that to run on mains gas.
You could then turn a dynamo generator to generate electric power, run the air cond and recover all the heat.

The system has been done commercialy for years and is called combined heat and power.

Quote:

---

Originally Posted by et0

Edit: I meant to say "central heating system". About 5kW worth of heat would be nice - any chance?

---

Not with a car air cond, it is not big enough. A truck refrigeration system would deliver it though.

Cheers taz.

Quote:

---

Originally Posted by taz24

In principle yes it would work, but it would not be cost effective.

What you need is a small car engine that can be converted to run on gas (lpg) and then convert that to run on mains gas.
You could then turn a dynamo generator to generate electric power, run the air cond and recover all the heat.

The system has been done commercialy for years and is called combined heat and power.

---

I don't have mains gas, but I do have access to free waste oil which the diesel engine will run on.
I am familiar with CHP systems too, but in terms of initial cost this is the best idea I have.

Quote:

---

Not with a car air cond, it is not big enough. A truck refrigeration system would deliver it though.

---

Really? I thought car air-con was good for about 12000 BTUs or so? Or does it not work so well the other way..

If it's not going to do the job I'd consider a multi-split-unit system running off a generator, but the cost is starting to get up there.

Quote:

---

Originally Posted by et0

I don't have mains gas, but I do have access to free waste oil which the diesel engine will run on.
I am familiar with CHP systems too, but in terms of initial cost this is the best idea I have.



Really? I thought car air-con was good for about 12000 BTUs or so? Or does it not work so well the other way..

If it's not going to do the job I'd consider a multi-split-unit system running off a generator, but the cost is starting to get up there.

---

Well if you have waste oil and a deisel then yep go for it.

You could get a second hand cooling system from a transport fridge and convert that (it works the same)
basicaly it could be easy to do, you just need to find all the right pieces.

Cheesr taz.

If you are just going to recover energy from the engine cooling air and exhaust, then all the energy is comming from the oil, you would be better with an oil burner to heat the water, no mechanical losses then.

Quote:

---

Originally Posted by monkey spanners

If you are just going to recover energy from the engine cooling air and exhaust, then all the energy is comming from the oil, you would be better with an oil burner to heat the water, no mechanical losses then.

---

That would be too easy... lol

Quote:

---

Originally Posted by monkey spanners

If you are just going to recover energy from the engine cooling air and exhaust, then all the energy is comming from the oil, you would be better with an oil burner to heat the water, no mechanical losses then.

---

OR..... just buy a good heat pump for your house and in your spare time, make your heat pump dream come true.;)

Fair enough :)

Can someone point me towards an affordable air to water heat exchanger then?

edit: heat pump, I mean!

How much can you afford?

Quote:

---

Originally Posted by monkey spanners

If you are just going to recover energy from the engine cooling air and exhaust, then all the energy is comming from the oil, you would be better with an oil burner to heat the water, no mechanical losses then.

---

The heat from the engine is a bonus - it would pre-heat the outside air slightly before the evaporator. The mechanical losses you mention are also producing heat, which could also be recaptured by the heat pump. In theory.

So, I should get more heat energy out than is present in the oil. And, the engine can also run a small grid-tied generator to offset some electricity use from the house.

I have done CHP before (without a heat pump) but found I needed far more heat than electricity, and it got through an annoying amount of oil. That led on to the above idea.

Quote:

---

Originally Posted by desA

How much can you afford?

---

< 1000. You can get a really good split air to air system for less than that, so it would pain me to pay much more.

This is a backup for a wood stove to replace electrical heaters so it's a "nice to have".

Quote:

---

Originally Posted by et0

< 1000. You can get a really good split air to air system for less than that, so it would pain me to pay much more.

This is a backup for a wood stove to replace electrical heaters so it's a "nice to have".

---

This amuses me - sorry.

So, you expect to pay less for a good heat-pump than for a split a/c? Really?

:)

Have you any idea of what technology goes into a reliable heat-pump? :cool:

Quote:

---

Originally Posted by desA

This amuses me - sorry.

So, you expect to pay less for a good heat-pump than for a split a/c? Really?

:)

Have you any idea of what technology goes into a reliable heat-pump? :cool:

---

Feel free to enlighten me, I'm here to learn.

Seriously though, what's so different, technology-wise, from a big inverter heat pump split a/c unit?

Quote:

---

Originally Posted by et0

Feel free to enlighten me, I'm here to learn.

Seriously though, what's so different, technology-wise, from a big inverter heat pump split a/c unit?

---

There's a long thread on this board about AWHP's. Take a look & see if you understand it all. If you do, then, you're ready to build your own.

:D

Quote:

---

Originally Posted by desA

There's a long thread on this board about AWHP's. Take a look & see if you understand it all. If you do, then, you're ready to build your own.

:D

---

There's dozens of threads about AWHPs, can you give me a link for the one you're talking about?

I've also conceded that it's probably more sensible to buy one, and that's why I'm also asking about prices to see whether that's economically viable. Can you give me any advice here?

I'm not in the UK, but local folks could probably steer you in the right direction.

All the best. :)