rev cycle ac/ radiator

[andrew215]

As you know, the heat cycle on the rev cycle ac, with overboard discharge, will not work when the water temp is below 50 deg f. (or mine won't at least, it freezes up). have been thinking about putting a radiator in the system, with antifreeze in place of the water intake/discharge. Has anyone ever done this? any ideas pro or con?
thanks

 

[Guest]

I'm confused: You are trying to extract heat from 10Deg C water to heat a boat to human temperatures and are thinking about using an air based heat exchanger instead?

So you must be in a place where the water is below 10C and the air is dry or warmer. Otherwise that would freeze up as well.

How about just increasing the flow by adding a booster pump. Make sure the booster pump motor is cooled with the feed water then you will not loose too much energy.

Alternatively, I suggest you head to the equator.

 

[PBooth]

Hi, you will find that at ambient temperatures below about 50 f, your heat pump will struggle to get much heat output whether using an air or water heat exchanger (condenser when in A/C mode). If the heat isn't there, the system can't transfer it to the inside unit (evaporator).

Peter

 

[Anonymous]

Freezes up? Working in F (are you in the US?), fresh water freezes at 32F and sea water at about 29F. I tested my Cruise Air dual cycle at Chichester Marina (brackish, where I was) over winter 2004/5 when there was a layer of ice on surface and I got plenty of heat with no problems. At least one other person down there was using his reverse cycle AC as well.

It can be done - I suspect that you will need to increase your water flow rate - mine is very substantial.

 

[andrew215]

Thank you for the information, you're probably right in that I should try to increase the water flow, although all plumbing is the recommended size. Thanks again..

 

[Anonymous]

Is this a marine reverse cycle AC? I'm sure it's supposed to work below 50F, it's pointless if not. What make is it? If the plumbing fittings are correct, are the seacocks correct and fully open? Are the pipes very long? Is it an old installation? If so, maybe the pipes have got muck in them? Somewhere in the manual it might give a figure for gallons per minute flow.

We don't use ours as part of our main heating partly because I don't want to wear it out - it would be a real pain to remove for servicing and we do like to have the AC in the summer! I wouldn't use the boat systems (Eberspecher or AC) for long term heating in a marina as you can use cheap convector heaters instead without wearing out your boat kit. One guy in Chi Marina winter 2004 left his Eberspecher on all winter as frost protection (it was running many hours each day) and by mid Jan it had failed. Must have cost him a packet in diesel and repairs.

 

[andrew215]

I checked with AC guru. The heat for the reverse cycle comes from the heat of compression, the refrigerant boils at a low degree and the compression causes heat which is transferred to the coils in the heat cycle. It appears as if my unit is not going into defrost mode periodically to clear any frost. He suggested that perhaps the airflow over the coils is to fast and the air does not have time to absorb the heat from the coils, also that the water flow may contain some air components which is causing a reduction in the water flow thru the piping, (less water freezes faster). In any event, will be checking all this in the winter. thanks for your inputs again.

 

[Anonymous]

Anti frost cycles are common when the evaporator is air-warmed but yours isn't. I think it unlikely that the evaporator heat exchanger is actually freezing but if it is then you would expect to see the flow of water slow to almost nothing, then stop. Then work again after you've left it for some time? What is, perhaps, more likely is that the flow rate is low and the evaporator is not being adequately warmed, not sub-freezing, but to a point where the coefficient of performance of the cycle has dropped from about 3:1 to unity, or even lower.

The information we'd like is:- Water inlet temp and outlet temp, and flow rate in l/hr plus the amps drawn from the mains and the rated output (heat) of the unit. With this, we can easily calculate whether the system is working anywhere near where it should be since we know the specific heat capacity of seawater.

 

[2Tizwoz]

If this reverse-cycle heat pump is properly designed it ought to function with even cooler water.

Is your water flow or evaporator restricted by dirt / marine growth (animal or vegetable) ?

The above is a diagram of an air cooled/heated outdoor coil system. Rather than an outdoor coil you presumably have a water/refrigerant heat exchanger. To control the tendency for the 'outdoor coil' to freeze up when heat is being drawn from it the 'heating cycle expansion valve' restricts refrigerant flow by measuring the returning gas temperature and if it is too cold it restricts the flow of liquid refrigerant. Your expansion valve may be stuck, the phial on the end of the capillary tube may have slipped out of position on the pipe, when was your system drier last changed?

I could keep going, but you could start with some of those.