Help & advice needed

[elemental]

Hello,
I'm a newbie to refrigeration, building a small DC powered fridge for use by a non-profit project....so I know nothing about this! I'm a super handy person but I badly need some expert advice to help me put this together correctly so all tips are very much appreciated :)

The main things I need to figure out are:
What size and length of capillary tube do I need?
What size return pipe do I need?
What is the best way to connect the piping? (this will be trasported alot by car so Im wondering what the most fail safe way is)

The approximate fridge size will be about 5cu ft with a wee freezer section about the size of 2 shoeboxes or a bit smaller.

I have purchased already a Bd35 that comes with a condenser and filter drier already piped up (chinese knock-off version from here: https://www.aliexpress.com/item/32812652209.html?spm=a2g0s.9042311.0.0.17fa4c4dKgydRD )

..and an evaporator: ( https://www.ebay.com/itm/Fridge-Freezer-Roll-Bond-Aluminium-Evaporator-20x10-525x250mm-1-4-tube/173149053318?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 )

[Brian_UK]

The evaporator gives sizes for the suction pipework, 1/4"ID 5/16"OD.

For the capillary you need to connect to the 2mm OD evaporator connection and you can size it using software from Danfoss available here.... https://www.danfoss.com/en-gb/service-and-support/downloads/dcs/dancap/

[elemental]

Thanks for your response Brian_UK :)
The specs for the compressor give two completely different figures for evaporation temperature -23.3 under LBP and -5 under MBP. Any advice on which is relevant for my application?
Also from what I can find available online it looks like I will only be able to get something close to the right size and length but not exact. Any advice on how I should judge that...what are the implications of too big/small, too long/short?

[Brian_UK]

Bear in mind that the evaporator you specified is only rated as a freezer at -6'C and you need the refrigerant to be perhaps 10'C below that, let's start with a suction temperature of -15'C.

Dancap will give you a preferred capillary size and I would start with a duty of 100 Watts ie a bit below the compressor maximum rating.

I don't know the capillary sizes available to you but it's easier to shorten it than lengthen it if required.

[elemental]

Ok. So I'm realising that maybe I don't quite understand what figures to enter into Dancap.
So if its a 100 watts is that the figure to use for Input data A - btu/hr? ie 100 x 3.412 = 341 btu/hr
Input Data B - evaporating temp is what is listed in the specs: -23.3?
C - Condensing temp: 54.4(from specs)?
D - Return Gas temp: 32.2(from specs)?

15511

[frank]

Ok. So I'm realising that maybe I don't quite understand what figures to enter into Dancap.
So if its a 100 watts is that the figure to use for Input data A - btu/hr? ie 100 x 3.412 = 341 btu/hr
Input Data B - evaporating temp is what is listed in the specs: -23.3?
C - Condensing temp: 54.4(from specs)?
D - Return Gas temp: 32.2(from specs)?

15511

If you scroll down a little further on their web site, you can see that the BD35H is for LBP application on R134a with a duty of 86W @ 3000rpm.

In your initial post you say that you are making a fridge with a small freezer section. This will be difficult to do as they each require different evaporating temperatures. I've attached a DanCap selection based on an evaporating temperature of -5C which will suit your fridge.

You can alter the settings of the DanCap programme to input Btu or W etc. - no need to convert from 1 to the other