What are the Economics of Super Insulating a Walk-in Freezer?

$400 a month with how much traffic?

At a certain point, more insulation won't help because essentially all your losses are through the door whenever somebody goes in.

...I can't tell you if that point is R25 or a formula to verify, but that sounds low to me as well.

 

I agree with the above about adding the curtains on the door if it’s going to be high traffic it’s a good measure anyway

50° walking here in San Francisco would not be bad are you keeping it in the house where it’s air-conditioned are you keeping it in a garage that is not conditioned and you live in a place where it hits 90 or 100° in your garage might get up to 110° ?

temperature difference makes all the difference in the world

There’s a heat load formula for every square foot of surface area to a known insulation value to a known Delta between the temperature of inside and outside you can calculate the BTU loss per hour.

because they walk in freezer of that size kept in my garage here in San Francisco California or the average daytime temperature all winter long which is about six months is about 58°F.

in the summertime her average temperature is about 68°F so you’re R28 value would probably be good here in San Francisco

but if he went to Texas and kept it in a an non-air-conditioned garage hits 100° plus in the garage would even get hotter R28 would not do so well.

If this has been purchased from a real freezer company With an educated sales person can follow the zone chart for your climate and then he would take that information follow his chart and they would already have the recommendations in a spreadsheet to make the correct sales to the correct climate zone. For software program since most everything is done by software now.

 

A more important question

can you use the heat the unit generates?

and if not is it being effectively vented so you don’t need to air condition your heated freezer vent air?

also the floor of the unit is likely the most critical to well insulate.

Also if this freezer is located in a perpetually air conditioned building your “losses” to the freezer help cool your building. As long as the freezer you choose is more efficient than your central air cooling your building is only a positive, not a loss assuming of coarse you properly deal with the hot air making sure it doesn’t heat unwanted areas

 

That also seems absurdly small to me. For homes in cold climates with smaller average (not worst cold nights) temperature differences than that, R-25 is the minimum for walls, and way short for ceilings.

That is 4,000 kWh/month, or 48,000 kWh/year, which is absurdly high for any normal home for all energy combined, let alone a single appliance. My all-electric home never exceeded 12,000 kWh/year when it used electric resistance heat, and is now down under 6,000 kWh/year thanks to various improvements and heat pumps. (And I generate all that with rooftop solar PV.)

But the back-of-the-napkin calculation below suggests a much lower energy need, maybe he slipped a decimal place? Or am I missing something big?

Doubling the effective R value will cut the energy loss in half, absent other loss mechanisms such as open doors. Beware that effective R value is less than the listed R value of the raw insulation, due to greater heat conduction from thermal bridging through studs and other structural elements. Though if you offset the extra outside foam panels from the inside panels, you can reduce that thermal bridging.

With R-1 insulation, you'd have a heat flow of 1 BTU per hour per degree-F per square foot of insulated surface (including walls and ceiling, not just floor). For a room 10x12' feet wide and 8' feet, that means (excluding corner effects and thermal bridging and any convective losses from air infiltration) heat loss = 592 square feet * 50 degrees = 29,600 BTU/hour. A true R-25 insulation would drop that to 29,600 / 25 = 1184 BTU hr, or about 350 watts. Allowing for those thermal bridges, make that 700 watts thermal. Assuming a refrigeration plant coefficient of performance of 2 (not leading edge at all), maybe 350 watts electric, or 260 kWh/month, or $26/month at your energy rate. Which seems suspiciously small, because it is similar to old era kitchen refrigerators with far less volume and wall area.

Absent some bone-headed errors or omissions in this calculation, I could imagine $40/month, but not $400/month.

 

My True 3 door commercial kitchen 73 ft.² refrigerator with a lot of active use approaches $40 a month extra electricity after installing in the house.
On a high use day it’s amazing how much heat could come off of one of these Commercial refrigerators and they’re a little noisy. Compared to our residential refrigerators.

 

$40 of electrically powered Air to Air heat pump “heat” is enough to heat a small home in a mild climate.


Traditional home Refrigerators are notoriously under insulated, focusing on useable interior area more than insulation (my 5 year old fridge has 1.5” wall width in many spots)
more efficient models just use more efficient cooling systems .

Although the net heat output of a fridge isn’t huge, (one part cools, the other heats, zeroing out some heat)
if you can isolate the hot side and the cold side you do end up with a pretty good separate cooling and heating system.

My relatively small fridge makes about 1000BTUs if you don’t subtract the cooling affect. (Which is also not insignificant)

Unfortunate most normal home refrigerators don’t at least offer preinstalled attachment points to have air vent / intake. My fridge is on an outer wall by a window so ducting in the summer would be easy.

 

i would love to duct the heat outside. 94 out, 76 in, only makes sense

 

In a temperate climate, divert-able ducting to choose to send the heat inside or outside would be a useful energy saver.

In a hot or AC-dominated climate, make sure the heat is dumped outside, not in the living space.

On a year-round basis, at OP's electric price, that could cover not just the heat pump heating, it could cover all the other electric needs of an entire all-electric household too. Though the house would need to be more energy efficient than average.

 

Also forgot to mention San Francisco California or most everybody is paying over the base price of PG&E rate instead of $.24 which is almost impossible to use that small amount of electricity that they give you a allotment were usually paying $.34 a kilowatt hour to $.38 a kilowatt hour and if you use way too much electricity they super penalize you at $.42 a kilowatt hour

and commercial kitchen refrigerators are not meant for efficiency

they were designed to be used in the kitchen with a lot of workers that will be continuously opening and closing the doors and this has three large doors.

they were designed for quick cool down because fresh dishes of food and products will be put into the refrigerators that needs to be cooled down rapidly and that takes a lot more energy.

so this is one of the disadvantages of owning commercial restaurant appliances in a residential house.

 

That example burns energy like a commercial facility, vastly more than an entire normal upper-middle-class all-electric home should use. At the example's electric price, it adds $5000 / year to the electric bill. What is your electric price? Note that plenty of areas charge double or triple the rate of that example.

In some areas with nosy utility employees or drug enforcement agents, you'd want to notify the utility just why your electric usage is taking such a huge jump. Otherwise, it just might be used as probable cause to get a search warrant to come inspect for an illegal marijuana grow house.

It would, if wall insulation is the only heat loss path. But that is normally not the only path. When a lot of heat flows through open doors or air leaks, all bets are off. Note also that when people double the wall insulation, they may not similarly double the door and door seal insulation, where a lot of thermal bridging occurs.

That is the nature of the reciprocal math. Compared to 1" insulation, a 2nd inch saves 50%. The next 2 inches saves 25%. The next 4 inches saves 12.5%. The next 8 inches saves 6.25%. The next 16 inches saves 3.25%. ... The return per dollar or inch of added insulation diminishes rapidly.

But the typical electric bill in the link above is totally out of whack for R-25 insulation. Either the cooler is leaking like a sieve, or the refrigeration plant is horribly inefficient, or the blower fan inside is seriously overpowered, or the room is being used to freeze a very large new mass of water or product every day. Or some combination of all of these.

A sample computation for an 8' x 10' x 12' box with R-1 insulation, a refrigeration plant with a coefficient of performance of 2.0, and the door always closed, gives a lower electric bill than shown in that link.

The example link is a decade old. I'd look to see if they have improved their thermal efficiency since then.

 

Once you are at r25 on a commercial 10 x 12 ft walkin freezer kept around 20f, air sealing is the best bang for the buck. So the door gasket, closing mechanism and refrigeration line penetrations are key. Most losses are staff keeping the door open as they access the space.

 

Yes correct the statement that doubling your insulation does not cut your losses in half.

it’s not a linear gain in insulation value.

on refrigerators and especially freezers in low temperature application the most crucial thing is the skill set of the installers simply throwing up the walls floors and ceiling is not good enough.

it’s how thoroughly they throw the caulking strips or whatever timer ceiling material they’re going to use in between the wall panels as there but it up next to each other.

The floor must be completely sealed every ceiling panel all those gaps in between.

One of the projects I’m working on right now I’m working on refrigerated rooms that we’ve installed that are 40 foot long 27 foot wide and 16 feet tall.

I noticed their contractor they hired to actually do the installation got the cheapest work he can for workers and it shows.

I told the owner that they were not doing it correctly.

and when all is said and done they were having a problem with the humid air being sucked in through the cracks in condensating in the difference in temperatures of the metal wall turning into water and pouring out the bottom of the inside of the walls this is a very common thing that over the years cause Foister damage more than mildew and the interior side of the metal walls to rot out.

where they set the ceiling panels on top of the walls was not flush and straight and they did a very poor job of putting in the foam insulation and I was able to prove this with my infrared camera showing all the cold spots and can see where all the air is infiltrating through the cracks and turning into liquid water on the inside of the panels and then dripping out at the bottom of the floor.

how airtight and sealed it is is extremely important.

and if you were to turn it into a freezer for example for ice cream -10 below zero to -20 below zero the problem becomes even 10 times more important to be airtight.

our walls are 9 inches thick and the ceilings are 12 inches thick.

 

Lech has a decent youtube channel for those who did not know. One of my favorite hvac channels is in the same general area of northern calif, eg NorCal Refrigeration. A mild mannered university industrial ac and refrigeration specialist by day, NorCal Dave turns into a commercial hvac SuperTech after hours and weekends with his custom university surplus Vangina.

For those who think a walk in cooler can be ordered from Lowes, here is the basic construction of this class of commercial cooler. This one is not a freezer but you get the idea.

 

If your not on a slab is there an opportunity to insulate externally in the floor joists below?

 

I believe a typical commercial facility has a lot of regular foot traffic going in and out, and a lot of product moving in and out. That means the bulk of the energy is blowing and flowing and being carried through the door when it is open, not through properly built walls.

Being in a commercial facility, its power consumption shouldn't arouse the same suspicions as a normal home. Even if it did, being a fixed asset, it would pass muster if they don't find a huge array for grow lights inside.

I think this would be a large factor in getting it done well.

Go back to the math I posted earlier. If the walls are properly built and sealed, the calculation should be in the ballpark for that portion of the energy load, even if it doesn't account for a far greater load due to door traffic and needing to re-chill new product brought inside.

If you add 2" extra to the original 4", that should drop the wall leakage load by 1/3rd. Where I figured $26/month, your added 2" would save about $9/month. Since R-25 insulation in a wall doesn't really make an R-25 wall due to thermal bridging from structural elements, offsetting seams to reduce those thermal bridges could get you 1/3rd of a somewhat larger number, but your savings would probably still be under $15/month.

In short, to get the electric bills in the sample calculators, the bulk of the energy loss is not through properly built walls. It is through the door, especially when open, and through leaks and other possible construction defects. Be on watch to minimize those.