Webasto FCF Reverse Cycle Freezing?

[a64pilot]

Originally Posted by DeepFrz

Has anyone noticed that many posts ago the OP stated his problem had been solved by setting the control to AUTO?

I didn’t, if it’s like my Webasto’s only function of auto is to select heat or cool based on temp, with I think about a three degree temp difference, but don’t quote me on the temp difference though.

[OzePete]

Originally Posted by a64pilot

I’d rather not argue, that was enough

If you read what has been quoted, I am not arguing either, but surely I have the right to disagree with commentary of my postings that is not correct.

Refrigeration is a very precise science with factors that are simply calculable, resulting in correct outcomes. No need for guesswork or assumptions!
Incorrect / misleading information is damaging but easily refuted/ corrected given the opportunity of discussion.

I always support my comments with refrigeration engineering facts and data gained from decades as a Refrigeration Engineer and systems manufacturer. My interest here being that readers are properly informed with those facts and data, (not puffery!) . I have no interest in winning a popularity contest but am always willing to help anyone with refrigeration issues if I can.
(I am rather handicapped these days and communicating via the web / phone with others keeps me sane.. well nearly!)

A64, I believe that discussion to and fro on this and other refrigeration issues is helpful as users become more informed as a result. This would be specially so if the issue being discussed is adhered to, without diversion.

Cheers, OzePete

[lancelot9898]

I haven't noticed my Webasto 12 K unit icing up which I've been installing over the past month. It's finally operating well after several modifications to the both the water flow and the air flow. Basically my water flowrate was not sufficient enough to keep the system from shutting down. And it would shutdown after just 10 minutes or so and with temperatures measured at the outlet air duct climbing to 120. My flowrate was just 4gpm and I was told to get to 6. I was able to increase it to 5gpm and now I no longer experience the shutdown. The heat pump will be able to extract heat down to around 43 degree water temperature, but the folks at Webasto said that I may be able to extract more is the flowrate is lowered. This would make sense since the compressor is adding heat and in heat mode the btu rating is 13K vs the 12K in cooling mode. So why am I not seeing the icing up, but rather just the opposite with low flowrates?? (Could it be that it was starting to ice up and that resulted in high temperatures coming from the duct? But I did not observe any ice. ) Maybe I better get out the thermodynamics books from long ago.

[a64pilot]

Further reduce the flow rates and you will ice up, you will also not be able to keep your hand on the compressor either it will be so hot.
I understand what Pete posted about return gas flow being cold with reduced flow rate and that keeping the compressor cold, maybe so much that you get liquid return, but that’s not what I see at all in mine.
What I see as the strainer and intake clogs is very high temps of the output air, and high amp draws, along with excessively hot compressor, then the system cycles the compressor off, I assume due to high compressor temps with no fault code, compressor cools and it restarts. This also agrees with what you heard from Webasto about being able to extract compressor heat.
This is on a Webasto 16K System.

Now of course airflow over the condenser in this case has an effect too, if it’s restricted then it can’t remove as much heat as it should.
A heat pump does exactly that of course, it absorbs heat on one end and dissipates it on the other, so we need to be able to both add, and remove.

[transmitterdan]

If the people at Webasto tell you to reduce flow rate to get more heat from the water run away as fast as you can. That is completely backwards. You want to run the water as fast as possible when cooling or heating for best heat transfer.

[Cadence]

Originally Posted by transmitterdan

If the people at Webasto tell you to reduce flow rate to get more heat from the water run away as fast as you can. That is completely backwards. You want to run the water as fast as possible when cooling or heating for best heat transfer.

I would suspect ambient water temp. would play into it?

[transmitterdan]

Originally Posted by Cadence

I would suspect ambient water temp. would play into it?

Can you explain how water temp matters in relation to optimal flow rate?

Running A/C in really cold water might make a difference but who does that?

[Cadence]

Originally Posted by transmitterdan

Can you explain how water temp matters in relation to optimal flow rate?

Running A/C in really cold water might make a difference but who does that?

Just a suggestion, possibly supporting the MFGs suggestion. I don't know what optimal is? Probably predicated on a mean water temp.. JMHO

[transmitterdan]

The warmer the water the more heat the process can extract. The slower the flow rate the colder the average water temp is inside the water/fridge heat exchanger. As flow reduces exit water temp reduces and eventually the water freezes solid at some low flow rate. Ergo higher flow rate can extract more heat.

There is no advantage to slowing water flow in a heat application.

[Cadence]

Originally Posted by transmitterdan

The warmer the water the more heat the process can extract. The slower the flow rate the colder the average water temp is inside the water/fridge heat exchanger. As flow reduces exit water temp reduces and eventually the water freezes solid at some low flow rate. Ergo higher flow rate can extract more heat.

There is no advantage to slowing water flow in a heat application.

I feel sure there would be an optimal flow rate at a given water temp.. Whether a manufacturer would incorporate it for efficiency is unlikely since it would be costly for average usage. Stock holders like return on investment.

[a64pilot]

Originally Posted by transmitterdan

Can you explain how water temp matters in relation to optimal flow rate?

Assuming your in heat mode as we are discussing here, the colder the water is, the more flow will be required to extract heat.
Where I’m at in S FL with water temps on the mid 70’s. The other day when it was a cold morning my heat pumps worked very well with reduced water flow, but if I had been up North with water temps in the 40’s, they wouldn’t have worked as well.
I need to Dive the boat and clean my strainers I believe, the other day I had to flush water backwards through my main strainer, the generator water flow stopped, the basket was slimy, but when I opened the thru hull there was no flow.
I’ll wait until I get to the Bahamas to dive the boat in clear water, ought to en in a day or so.

[OzePete]

Originally Posted by transmitterdan

If the people at Webasto tell you to reduce flow rate to get more heat from the water run away as fast as you can. That is completely backwards. You want to run the water as fast as possible when cooling or heating for best heat transfer.

Agree 100% to both comments.
Advising to reduce the water flow to get more heat and a previous comment suggesting a partially stuck reversing valve could be causing the ice up... what absolute nonsense.

Cheers OzePete

[dkenny64]

we had a partially stuck reversing valve on our old unit..
this didn't cause icing..but it caused the system to trip the breaker when it tried to cycle on/off then on...why? too much head pressure on the cold side..if the unit was manually turned off( just changing the temp setting) for 10sec..then turn on back to normal all was good..



I don't think having to run a system on auto mode is the total answer..
we have this system and is work in all mode..fan and heat...
side note..what I would like to know is how to make the webasto keep the fan on...just ON! I don't care the compressor/reversig valves/ water pump are doing..fan on. high/med/low - off topic.. I might need to contact Webasto


-dkenny64

[lancelot9898]

Right here is an observation. With a 4gpm flowrate(which is on the low side) I was getting a temperature reading from an outlet duct of 120 F before the system shutdown. Now in heat mode that might be a good thing if you could harness that extra heat. So the specs for the 12K system shows that in heat mode.....it's 13K. Could it possibly mean that some heat is being produced by that compressor ? Now I don't have time to go back and make a presentation showing mathematically what is happening nor do I think I can remember the equations, but those are the observations that I observed!

[a64pilot]

I have a theory on why the OP’s works now on Auto.
With the Webasto, there are two auto’s, auto fan and auto AC/Heat.
If the temp isn’t really close to set point in auto fan, the fan runs at high speed, on the Webasto there isn’t a whole lot of difference sound wise between low and high fan, but of course high fan does move more air, if his airflow was restricted over the coil which in heat mode is the condenser, then the air is going to get hot and the compressor very hot too.
So he may have an airflow problem.