Danfoss BD35/Frigoboat problem

[Neptune's Gear]

Actually, there are PLENTY of stories about air cooled units failing, or being inadequate in the tropics.

Many installs also end up running almost full time, and get turned off, due to the large power requirements.

The OZE fridge units have the advantages of both, as they can be both Air AND water cooled. BUT they use FRESH WATER- they don't consume it, just borrow it and return it slightly warmer. No anodes, no marine growth, no thru hull to suck in rubbish etc. Really simple, and really efficient. We have Ice cream on the equator - our freezer temp varies from -15c to -22c as that is the cycle I have set. Have a look on my web site below, and click on refrigeration if you are interested.

Cheers
Matt

[Richard Kollmann]

Holding Plates serve only one purpose and that is to store surplus alternative energy if and when it is available. Compressors smaller than 1000 btu rarely produce any surplus energy.

After designing, manufacturing, and testing more than 200 holding plates it is my opinion standard evaporators provide better box temperature and better energy performance than holding plates.

[SV THIRD DAY]

Originally Posted by Neptune's Gear

Actually, there are PLENTY of stories about air cooled units failing,

Can't seem to remember or find a story of an air cooled condensor failing. Of course all cruising gear has a certain failure rate...it's the nature of cruising gear. Looking through our warranty paperwork that goes back to 1973 we have had only 5 (edited from 3) air cooled condenser failures out of the thousands of systems we have out sailing around the world and tropics. But it sure seems like everytime I visit the Cruisers Forum there is a tale of woe about a water cooled condensor failing. I can't find simular posts about failed air condensors. Over-heated Electronic control modules failing from running 24hrs/day...well that is another story all together!

The trick with air cooled units is to size the condensor large enough to be able to handle ambient temps of up to 120 degs F without needing water cooling. I've spent 4 summers in the Sea of Cortez floating in 90-deg water and even in that brutal environment, the inside of our boat never came close to getting above 120 degs. We supply the millitary with 12v refrigerated food storage containers for use in desert environments where water cooling is not available and their spec was for the unit to function properly up to 135-degs. Now if I was ever floating in my boat with a temp anything close to 135-degs, I would get out of there REAL FAST because my ice cream wouldn't be the only thing that is melting!

[Neptune's Gear]

Hi Richard,
OK, so this is something I don't follow. But then, like most yachties, I'm not a refrigeration engineer.

My thoughts are; If the compressor system cannot produce ANY surplus energy, and therefore cannot store it, it has NO holding power, and must run all the time to maintain the required temp. If you then move to a hotter location, surely it would then not reach that "desired" temp? Seems like if there is NO reserve capacity, the unit is too small?

In my install, the holding tanks/Plates freeze down solid, as the temp is reduced to -22c. They then Hold the freezer down for a considerable period - the compressor runs about 30% of the time at the equator. This is not theory, that's what happens, and, in my experience over 40 years is what most cruisers want for their systems.
Is that not correct?
Cheers
Matt

[Moonos]

My whole reasoning for wanting a holding plate system is you can run it a few hours a day when the motor or generator is on anyway so you have plenty of available power.

Less motor starts per day would also lower daily amp hour usage.

I would wire it up with both manual and auto control. Just be careful having manual control as things can go bad if you forget about it.

[Neptune's Gear]

Originally Posted by Moonos

My whole reasoning for wanting a holding plate system is you can run it a few hours a day when the motor or generator is on anyway so you have plenty of available power.

Less motor starts per day would also lower daily amp hour usage.

I would wire it up with both manual and auto control. Just be careful having manual control as things can go bad if you forget about it.

That's what I thought originally when I installed ours. But, because it works so well, we now just leave it on - all the time. It has a control system that watches the batt voltage - so whenever the is "excess" electricity (like motor started, batts up due to Wind gen or Solar) it will start up the freezer system and make sure it is at max cold, while the power is there. No need for a manual switch! It's a really well thought out, clever system.

[s/v Jedi]

It's pretty easy: a holding plate is a battery for storing "cold". Like an electric battery, what you put into it, you can't all get out, i.e. there is a loss.

When boats have a wind generator or solar panels, the 12/24V DC Danfoss compressors coupled to evaporator plates will always give the best performance because nothing gets stored in the process of cooling the box: the electric energy generated by the solar panels, is fed to the compressor instead of to a battery where part will be lost. Then the refrigeration unit converts this electric energy into "cold" which is directly put into the box where it is needed, instead of into a holding plate where part of it will be lost.

On the other hand, it you have a big compressor driven by the engine or by a big electric motor for which the genset must run, then you want to minimize runtime, so you make as much "cold" as possible and store it in a holding plate for later use when it is needed.

So, the shift towards 12/24V Danfoss compressors and evaporators is due to the popularity of solar panels and wind generators, which is an environment where these will beat the big compressors and holding plates hands down.

[SV THIRD DAY]

Originally Posted by s/v Jedi

It's pretty easy: a holding plate is a battery for storing "cold". Like an electric battery, what you put into it, you can't all get out, i.e. there is a loss.

When boats have a wind generator or solar panels, the 12/24V DC Danfoss compressors coupled to evaporator plates will always give the best performance because nothing gets stored in the process of cooling the box:.

There may be some false assumptions made in that statement.
The CoolBlue unit with holding plate, thermally adjusting expansion valve, drier/receiver and large air cooled condensing unit will use about half the power of a critical orifice thin evaporator plate. (The dryer/receiver stores the 24oz of refrigerant in the CoolBlue compared to the 3.5-5oz in critical orifice systems, which is key in why we don't need water cooling by having a much larger air cooled condensing unit compared to the cirtical orifice thin plate systems)

The common mistake comes in thinking that the two systems operate at the same efficiency to remove the same amount of heat, but they don't. If they did...then the argument about holding plates being only a "battery of cold storage" would be more accurate and it's what confuses people along with the difficult nature of getting good side-by-side comparative testing data. A technical understanding problem comes in that not all holding plates are equal. Some are simply critical orifice evaporators inside of the holding tank, some are just copper tubes zig-zagging through the plate, while other have a thermatically adjusting expansion valve and high surface area fin-tube evaporators inside the holding plates to optimize efficiency of the compressor.

Side by Side testing showed that the fixed orifice thin evaporation plate style unit will cycle on/off about 175 times in a 24hour period where the CoolBlue holding plate system compressor cycles on/off for 4 times during that same 24hr period.
The critical orifice evaporation plate system (AB Cold Machine) used 48AH in 24hrs, while the CoolBlue holding plate system used 24AH. Same box, same test condition temps, etc.

Techautics hasn't been in business since 1968 by advertizing fake Amp hour usage data. There are plenty of real life cruisers out there to vouch for our amp usage data compared to the critical orifice evaporation plate systems they replaced and I'll be happy to share test data with those interested. Just shoot me an email at Info@TechnauticsInc.com

[Boatguy30]

Whew 175 times a day! My Nova Kool freezer used to run 20 minutes every hour (roughly) air cooled in the tropics. Was running on the slowest RPM setting.

[Neptune's Gear]

I have to agree with Rich, it's not that simple. Our unit uses holding plates/tanks, and generally cycles on/off 3-4 times a day in really warm temps, where the freezer is 50 deg c (or more) cooler than ambient. (provided the cabinet is reasonably efficient)
You are talking about thermal mass in the freezer. Holding plate systems have more thermal mass, and therefore stay cold longer, given that the losses from the freezer are equal. Therefore the time between switch off and on again is greater.
It is also really important to ensure the fluid in your holding tanks is actually frozen before switch off. The change of state from frozen to liquid requires many times the energy than just a cold liquid adjusting by the same temp. Many systems are not set up correctly - ie with the correct mix to achieve this.
AND the water cooled system mean no heat into the cabin, without external vents. ANY extra heat in the cabin is too much in the tropics in my opinion!
Each to their own though, you must make your own calls for what you like, or think sounds sensible! Testing it on the equator and finding it lacking is NOT what you (or the Admiral) want.

[s/v Jedi]

I'm sorry, but efficiency is not a matter of opinion: it is something that can be determined factually.

Cycling of the system does not determine energy usage. What does determine the energy used for cooling your box is the power consumption of the system times the number of hours it runs each day. If a system is 800W and it runs 6 hours a day, then it's consumption is 4.8kWh. It doesn't matter how often is switches on and off.

Now, the modern Danfoss compressors will actually try to run as long as possible, instead of as short as possible. In order to do this, they support a range of speeds; many support 6 speeds or so. To run for longer, they switch to a lower speed. The reason is that the efficiency is improved that way, minimizing energy usage for cooling the box at the same level.

At the same time, they use power from your solar array or wind generation for extended periods, meaning that this power does not need to be stored in batteries: it is used right away without any losses. For most boats this is a 20% improvement right there.

The loss of a holding plate is related to freezing a liquid to a solid and then thawing it afterwards: the freezing part requires more energy than what you get out while thawing. This adds to the loss.

Things like accumulators, expansion valves etc. do not have a positive effect on efficiency. When a Danfoss compressor with aluminium evaporator plate is matched with the box it cools (that is where it often goes wrong for DIY designs) and it's charged is accurately tuned, then my case is that it can't be beat by any holding plate system that is electric driven. It will win every time.

Adjusting a system with expansion valve is easier because you can adjust the valve instead of having to adjust the charge of the system. My current Danfoss based system is 5 times as efficient as my old Glacier Bay system, and it requires maintenance once every 5 years while the GB required maintenance almost weekly. And that was with the famed spider coil holding plates etc.

[SV THIRD DAY]

Originally Posted by s/v Jedi

Things like accumulators, expansion valves etc. do not have a positive effect on efficiency.

Thanks for the feedback Jedi.
It's great to know that everything Technutics has done since 1968 has been based on bogus efficiency claims that Randy (founder of Technautics with graduate work in thermodynamics) was able to hide from the public until now...

All that side-by-side independant testing is just a figment of someone's imagination....

The test box runing at the office with a CoolBlue holding plate system operating side-by-side with a critical orifice thin evaporator system isn't real and it doesn't exist in the real world outside of the internet.

And so we see the dangers of the internet, belief and opinion trumping science and data. Take this for example:

Originally Posted by s/v Jedi

The loss of a holding plate is related to freezing a liquid to a solid and then thawing it afterwards: the freezing part requires more energy than what you get out while thawing. This adds to the loss.
.

All that would be good and bolster your opinion, if only it was true and accurately described how holding plates work, which it doesn't. In a properly designed and working holding plate system you would NEVER let your freezing liquid thaw or defrost. Why would you ever want to pay the phase change engery price needed to go from a liquid to solid every time your unit cycles...that would be crazy and would negate one of the advantages of a holding plate system. What actually happens is that once you spend the phase change energy to go from a liquid to solid, you never again let the freezing liquid defrost. You take advantage of it's eutectic properties and change the temperature of the frozen mass as the compressor lowers the temperature and then the heat absorbed raises the temperature. The systems thermostat is set to keep the holding plate's freezing solution frozen.

Oh we can get into the scientific discussion about what is a true eutectic solution and what isn't...but years of testing data (not opinion or belief) shows that a properly designed holding plate system will beat the pants off a critical orifice thin plate evaporator in terms of daily energy usage. Now there are advantages to the thin evaporators, life is never an all or nothing game, but when it comes to daily power usage, something very important to a cruising boat, we literally have decades of data showing which style comes out on top.



Cheers

[Neptune's Gear]

Indeed Rich, I agree. I also could have worded that earlier post better. It takes a while for the whole mass to freeze solid, which it should have done before switch off. You are correct again, once that happens it should not return to liquid unless the unit is switched off. My point is that many units do NOT freeze. Ever. In my experience because no-one has ever explained this to the owners.
Jedi, what you say is not quite right. The unit I'm talking about is powered by a danfoss compressor AND it runs for a shorter time. That can't be bad - the current draw is lower, as the compressors are similar, but the run-time is shorter due to various design parameters incl the efficiency of water in removing the heat. Like Rich's one, the figures are available to anyone who wants them...
CoolBlue sounds pretty good as well, but I'm not familiar with them. Yet....
Matt

[SV THIRD DAY]

Look, I’m not trying to be a know-it-all-ass, despite what some would think, including my wife is she ever reads this post. I really do try to keep my smart-ass sarcasm/humor in check, but I’ll openly admit I fall short pretty often. The problem is that when faulty information is given out about my product’s technical specs and operation what am I supposed to do? (Yes, I’m the owner of Technautics CoolBlue Refrigeration...I try to point that out as full disclosure) I’ll tell you what all of the marketing and public relations experts say,

“Don’t say anything and never engage someone who disagrees with you or has a negative impression about your product on an internet forum. Don’t read chat forums discussing your product and for God’s sake, never respond or get into a technical discussion on the internet, that is certain death”.

That’s advice many of my fellow Boat Show Carnies talk about and follow very strictly. My “problem” is that I was a live aboard cruiser and an avid participant in cruising chat forums long before I became a low-life-boat-gear-pusher, and still living aboard I continue to have that mentality. I’m also just hard-headed enough to not follow the conventional wisdom, so when I see posts dealing with my products, something I live and breathe 7 days a week (water makers and Refrigeration), I jump in if I have something to contribute to the conversation following three simple rules.

Rule No 1:
When I don't know the answer to a question...don't BS and act like I know, because there is always someone smarter than me in the room.

Rule No 2:
Remember that no matter how good I think my gear and equipment is, there WILL be someone who doesn't like it and can argue their point more affectively than I can.

Rule No 3:
Having been at anchor in La Pax, MX with 8 boats that had my water maker installed on their boat, remember the guy I piss off today online, will be anchored next to me tomorrow!

My approach can cut both ways. Some cruisers view this openness as a plus in dealing with me and my products while I’m sure others take it as sleazy sales and marketing. I’ve given it a lot of thought and in the end I think the cruising community is better served when the relative experts in their field (at least that is what people building and selling gear should be) get involved in discussions of their product. Not as a way to sell more crap, but as a way to help educate fellow cruiser. I sure wish the owners of some cruising gear I’ve bought would give me and other cruisers the time of day and be publicly accessible to handle questions on their products. Heck...public accountability to your clients is a wonderful thing to insure quality and customer service.

[s/v Jedi]

You guys take a commercial approach while I have the engineering approach. You completely ignore everything I write about how energy consumption is measured, orobably because you don't understand it. But that doesn't stop you from denying it using arguments about how well a manufacturer tested it. Right.