Calculations on front opening fridges

[kubota]

thanks for the replies.

no, i don't use square wave inverters.
give me some credit guys. i actually heard
about the discovery of the wheel somewhere.

power factor is a characteristic of ALL ac systems including your sine wave inverter. ill be happy to give a working practical explanation somewhere outside this forum. the math explanation is too vector laden to be much fun.

all my measurements were done with tektronix and fluke equipment on both a xantrex 7000 watt and a magnasine 3000 watt pure sine inverter and side checked with less rigor on a mecc alte generator head on a commercial isuzu generator. im fairly confident of my numbers. also cross checked results with a commercial utility lab which declines to be mentioned by name.

for data, i simply went to lg's energy star rated appliance sub page and pulled off their 685kwh/yr for a 28 cubic ft unit which is about 1m3. i use energy star numbers cause those are gov verified and controlled. manufacturer numbers get wonky with test conditions so i generally don't trust them. if there is a better unit, shoot me a model number.

and off subject, but you asked.

yes i have a lab and it's the best thing i ever built.

i built my own because:

1. it avoids intellec property and patent issues with the university
2. most commercial clients don't have appropriate facilities in their production environ
3. back in the mountains off grid i have an extremely quiet rf and electronic noise profile. im dealing in nano and pico amps on some of this stuff and one bad led bulb will trash a system measurement with rf hash.
4. after 30yrs married and living on a boat my wife is happy to have me in my own location upon occasion.

if u do it, i split into a clean lab and a dirty lab in separate buildings. both metal for shielding of signals.
drilling and mounting and board production (cnc mill) goes on in dirty lab, instruments and software along with bourbon is in clean lab. amazing how little it costs anymore to get up and functioning with instrument prices down and if you dont have building codes driving up cost of facilities.

cherrio
g

[Toccata]

By Sailingunity
Second issue - our fridge faces athwartships and items would shift when heeled, opening the fridge on a port tack was sometimes a gamble. Not a problem if your fridge faces bow/stern

Third issue - space - you can stack things in the top opening fridge and use up much more of the space than you can with shelves. Yep, you have to pull stuff out to get to what you need. My new design is shallower but wider and longer, so there will be less digging needed.

Thanks Sailingunity.
Real world experience is invaluable. I'm still wrestling with the decision. Cost may become a factor, initial numbers (in Aus dollars) 6 to 8k estimate by a shipwright, to build a custom top opening well insulated grp box fitted with Ozefridge machinery. vs approx 6k for a 200litre Isotherm side by side fridge freezer unit. (Problem with that particular item is fitting it through a normal door opening on a boat)
The space efficiency argument is very valid. All available space is at a premium on a boat.
{Re my earlier post; my sister in laws qualifications to "run the numbers" Chemical engineer, Yr 12 maths/physics teacher, runs masters program at local uni for science teachers.}

[kubota]

in ac power

watts = Vrms x Arms * pf
where pf is between 0 and 1.
we sometimes refer to kVA instead of
watts cause your inverter actually has to produce kVA.

in a strange twist, the worse the power factor
the less the load looks in watts but higher the load in kVA. (one reason why best battery chargers are pf corrected and expensive so they work better with gensets).

SO:
best way to measure is to use a dc ammeter
on input to your inverter along with a voltmeter
and multiply the two to get true watts input while fridge is in various cycles.
this will account for all losses and give you a true picture of ac fridge energy use.

i use a recording device to give me a constant track over time. an amp hour meter is insufficient as it doesnt account for battery voltage variation.
a proper dc (not ac) kW-hr meter or kiloJoule meter works also.

so until you measure in a lab or on your own boat with your inverter and setup, you can't say anything determinate about ac fridge vs dc power consumption on an individual basis.

[kubota]

for bout $100 i could build a small device we could mail around to owners of both ac and dc fridges.
clamp it over wires (no breaking connections), turn off all ac loads but fridge, hit the test button on your phone, let it record for 4hrs, then upload data to server from your phone along with type of fridge and inverter (or dc) tested so results would be consistent. pull together in nice graph so decisions are obvious.

i am way too swamped to coordinate, but hdw dsn and build fairly easy.
wonder if any manufacturers would sponsor?
always thought this is the kind of real data cruisers forum should crowdsource, archive, and make available.