Commercial fridge build help sought

[LanceR]

I hope that some of you can check my planning process in laying out the basics of a stainless steel fridge smoker build.  I'd appreciate any insights.

The smoker will be used for cold and hot smoking with a max temperature of 225 F.  If I want to do traditional BBQ I'll light off one of the several smokers we have.  I see this as primarily for sausage, hams, bacon etc.

The insulation is polyisocyanurate which is rated to 300 F so I plan on leaving it in.  The walls have a hair over 2-1/2" of insulation and the door has a hair over 1-3/8" of insulation.  Figuring the insulation vale at R6.25/inch and the average thickness of the walls, top and bottom the average R value of the cabinet is just under R14 not counting the two layers of stainless steel.

The interior measures 22x26x60 inches so it is just under 20 cubic feet.   Playing with a 200 F heat rise to account for cold days a couple of different calculators average results come out to about 4400 BTU/1300 Watts per hour.  I figure on at least double that for loss out the exhaust, opening the door, faster temp recovery etc so that leads me to a minimum heat element of 2600 Watts so for giggles and insurance maybe a 3000 Watt element?  I think I did the math right but any help would be appreciated.

There is 30 Amps of 230 volt at the smoker location so power is not an issue.  Even with a 10% de-rate there are about 6000 Watts available.

We'll be using a PID controller for heat and at least two probes.

I plan on an AMNPS for smoke and will locate that over the air intake to be sure it doesn't get starved for oxygen.

My thoughts for the intake and exhaust are around 4" intake and 4" exhaust, both with dampers.

I'm thinking of using the top 2/3 for smoking so that leaves me about 20" at the bottom for the AMNPS, heat element, baffle plates, etc.  I'm thinking of having the AMNPS at the bottom with one baffle plate, then the heat element with another baffle plate.  The element will be centered in the unit. 

I think I will use a drip pan on a shelf under the product as needed rather than try to build something in that forces the heat to the outer walls.

I want to have fairly tight control of the humidity if that can be done without getting to the stage of over complicating things.  I'm most concerned about being able to stay in the 75-85 % humidity range for cold smoking.  I'm looking for any advice on how to manage that.  Maybe with a humidistat and removable ultrasonic humidifier?

The refrigeration unit still works so I'll disconnect the controls and pop it off the top of the fridge and save it. 

So, after all this long windedness the questions are:  Does a 3000 Watt element sound about right?  Any thoughts on humidity control?  What am I missing?

Thanks.

Lance

 

[daveomak]

Lance, evening....  Well, here's what I'd do..... I'd get 2 elements.... 1500 Watts each.....  Once the food and smoker get up to temps, switch off one element....  Program it into the PID...   I use a dimmer switch on my MES and really like running it at lower wattage..... Seems to be a lot more consistent temps and reduced temp swings...  Now, you are reading something from a guy who don't know squat about electronics... Just thinking out loud.....    Dave

 

[LanceR]

Dave, thanks for the thoughts.  I'll share them with the son who will likely be either building or buying the PID set up.  We have a pretty complete shot here at the farm and already mess with some custom controls. 

I'm obviously still in the head scratching stage.  I'm somewhat more concerned about being able to hold 140 or less for cold smoking sausage without temp spikes than I am about getting to 225.  I have an assortment of wood burning smokers for traditional BBQ so I doubt this critter will see much more that 180 very often.

Lance

 

[dward51]

Sounds like you have a good handle on it. 

There are a lot of builds that just use a single 1,500 watt element so I think your 3,000 watt version might be overkill.  I would come up to initial temp and recover from any door openings pretty quickly though.  Once the cabinet is up to temp and the meat stabilized from the initial load, the cabinet is insulated and will be pretty efficient at holding temps.  I'm like Dave, if you go with 3kw of heat I would split it so you can turn one element off for most of the smoke (especially if you are not going to over 180* most of the time).

 

[LanceR]

Thanks. I'll plan on two elements.

Any thought on humidity control? It hasn't really been an issue to date but then I've been using much smaller smokers for cold smoking sausage.

I'm looking for a humidity sensor that could control the humidifier and a fresh air circulating fan.  Frankly, I'm trying to learn what I need as I'm not even sure where to look or what such a thing would be called.

Any thoughts on a controller type?  I'd like to keep that in the $200 or at most $250 range but am open to other ideas, especially if I can use it to maintain the humidity.

Lance