retrofit hot gas defrost?

[knighty]

built a new freezer, 8m x 11m, 3m high (26ft x 36ft, 9ft high)

already have 2x 30hp Copeland semi hermetic systems to moved over to it (overkill, but might need to be used as blast freezer now and again.... long term only need to run 1 system)

would be great if the evaps can be mounted side by side at one end (8m / 26ft wide)

there's enough room to mount them and access them, but then there won't be enough room to change a defrost heater if one ever craps out

my plan was to fit a bunch of extra elements before mounting the evaps, so if one ever dies it can be disconnected and another connected

someone suggested retrofitting hot gas defrost, I've never seen that in person

looks as simple as a solenoid mounted on a 'T' on compressor exhaust, connected to evap on low side of the TXV

anyone have any opinions/advice/input?

I'm wondering about possible problems melting a heavy ice build up - if the system stays in defrost for a longer time is there not a point where the refrigerant is cooled too much to be effective?

[RANGER1]

Knighty,
Usually hot gas you defrost one evaporator at a time, as the hot gas has to be generated by load from other evaporators.
If evaporator not designed for hot gas it can require a few modifications on distributor.
Need good size suction slop pot with boil off coil (liquid line), a number of solenoids & pressure regulators.
To hard & expensive I think, buy purpose built.
Others may say no problem, easy!

[knighty]

hi Ranger

thanks for that - I didn't know about load provided from other evaps... makes perfect sense now

there's plenty of holes for more electric heaters... I'll buy a bunch... if a heater dies I'll disconnect it and connect a spare one

thanks again

Alan :-)

[frank]

you could always install the evaps in a staggered configuration at one end so that the heaters could be replaced on one unit if they fail and the other unit can be dropped if the heaters need replacing while the second evap is in in use

[knighty]

I thought about staggering them.... but I worried someone will hit the front one with a forklift!

I think a bunch of spare heater elements is the best move right now.... later on if an evap needs to be dropped then fair enough :-)

[RANGER1]

Ports in the walls, if suitable for that site!

[Tycho]

Knighty, no disrespect, but hot gas defrost isn't for your system, it would be too costly for the benefit.

I worked on a system like that 20 years ago, and we were 3 guys scratching our heads to the point of going bald to figure out how to mount the evaporators so the heating rods could be replaced.

There we were, A fridgie with 40 years experience, a fridgie/welder with 10 years experience, and me, 2 year and 6 months (if you count my 2 year apprenticeship :)), we are in there in the freezing room, staring at the ceiling, placing the evaporators side by side will make it impossible to get the rods out of either one of them, because the rods go out on the same side on both, so the rods on the left one will hit the right one, and the rods on the right one will hit the wall.

So there we were the best guys my company could send, and me (tool carrier and general slave), standing there in the middle of the freezing room wondering how the hell we can do this, and still be able to change the heating rods if they should fail. we were talking about staggering the evaporators, but it couldn't be done, because it would be in the way of the forklifts when the lifted produce to the top shelf.


We were in the North of Norway, and in walks a guy in his 40s, a Sami guy, he's a forklift operator at this fish factory, and has probably been since he was 10 years old.
Sami people are masters of language, they can put you down, be sarcastic towards you, be friendly and you as a listener can't be sure which one they are using... it's kinda uncanny, A Sami person can walk up to you and ask "So, I see you are doing good" and it could be a good thing, bad thing, sarcastic, you just need to learn to listen :)

So anyways this guy rolls in "So I've seen you guys in here staring at the ceiling for 2 hours, are you religious or is there anything you need to know about how to install this new freezing system, because you know, I am somewhat of an expert" and then he laughed and made to leave.

The 10 year guy chipped in and said "hahaha, no we are just trying to figure out how to mount the evaporators in the ceiling so they are out of the way of the forklifts and still be able to replace the defrost elements if they fail"

We had the evaporators open so the elements were exposed.

The forklift guy said very confidently "well, all you had to do was ask..."

Then he walked over to the evaporators, looked at them for like 3 seconds, then came back to us and said...

And this is a true story!

"I don't know what you experts would have done, but if it was my job, I would have moved the elements around so they can be pulled out in the middle, then mount the evaporators a a slight angle towards each other so that all the elements could be pulled out towards the middle without hitting the other evaporator"

Then he walked back, jumped onto his forklift and drove off...

I had no idea what just happened...

The 20 year expert looked at the 10 year guy, the 10 year guy said "I don't know" then the 20 year guy said "shut up and lets realign all the heating elements"

[NH3LVR]

:o Good One!

[knighty]

I'm lucky, these evaps have plenty of spots for more elements... so I ordered 15 for each

I'll swap out the ones that are in there right now for new (one is damaged anyway)

3 phase system, old ones are setup with 2 in series with a different phase on each end

new ones are 240v (mains voltage here) I'll wire all of one end together and run a negative to it too, then can join up the other end to the phases as/when needed

15472

all the holes pass right through the evap - some of the holes (all the used ones plus a couple extra) have liners in them - a tube for the element to pass through.... non of my other evaps are like that... I'm ok to put the elements straight through the evap/not in tubes yeah?