Cool The Shop With A Thermal Battery-Based System

This film projecter is hiding an Arduino Uno that controls a water-based cooling system.

Having any kind of shop is pretty great, no matter how large it may be or where it’s located. If the shop is in an outbuilding, you get to make more noise. On the other hand, it will probably get pretty darn hot in the summer without some kind of cooling system, especially if you don’t have a window for a breeze (or a window A/C unit).

Five 55-gallon tanks of tap water are buried just outside the shop.[Curtis in Seattle] built an awesome thermal battery-based cooling system for his shop. The battery part consists of five 55-gallon drums full of tap water that are connected in series and buried a foot underground, about two feet out from the wall. There are two radiators filled with water and strapped to 20″ box fans  — one inside the shop, which sends heat from the shop into the water, and another outside that transfers heat out of the water and into the cool night air. Most summer days, the 800-square-foot shop stays at a cool 71°F (21.7°C).

We love that the controls are housed in an old film projector. Inside there’s an Arduino Uno running the show and taking input from four DS18B20 one-wire temperature sensors for measuring indoor, outdoor, battery, and ground temperatures. There are four modes accessible through the LCD menu — idle, cool the shop, recharge mode, and a freeze mode in case the outside temperature plummets. Why didn’t [Curtis in Seattle] use anti-freeze? It’s too expensive, plus it doesn’t usually get that cold. (Although we hear that Seattle got several inches of snow for Christmas.) Check it out after the break.

If you can’t just go burying a bunch of 55-gallon drums in the ground where you live, consider building a swamp cooler out of LEGO.

Thanks for the tip, [Zane Atkins]!

64 thoughts on “Cool The Shop With A Thermal Battery-Based System

  1. For the non-US-Americans (or for those who don’t know the specific heat capacity of water in kilopondmeters per fl oz from the top of their head)

    · 55 Gallons = 250 l
    · 5 of these drums thus contain 1250 kg of water
    · 20 ” = 0.5 m
    · 800 square feet = 74 m²

    And water has a specific heat capacitof 4200 J/kg/K, so to heat the full volume of this system up by 5 °C, you need to extract 26 MJ from whatever is cooled with it.

    A human sitting around not doing anything in particular produces 200 W of heat. So, that’s 720 kJ an hour; meaning that if this whole water mass was 5 °C colder than the room before, after 36 hrs of 100 % efficiently transferring the human heat output to the battery, it’s at room temperature.

    1. Foiled by the imperial system again. Those are not ‘normal’ ten-pound gallons. Those are the funny stunted American gallons: 3.8L each.
      Those barrels are 200 liters each, or a nice round tonne of water.

      1. I never realized a British gallon is the volume of 10 british pounds of water. And I now found out a US gallon is 0.8British gallon – until you are talking the dry gallon (bushel), which is a little greater than a British one!

        Thanks for trying to convert, but using pounds to explain stuff is only more confusing as a metric pound is just .5 kilo.

        I think most metric hackers are used to measures being given in imperial and have rules of thumb for converting them.

        Temperatures are still impossible for me to convert by head. I also found recipe units difficult to get a feel for, until I realized a “cup” is just a large drinking cup.

        1. There are 180 degrees F between the freezing and boiling points of water. There are 100 degrees C between those points. So to get degrees C subtract 32 from F then divide by 1.8. To go from C to F multiply by 1.8 then add 32. If you’re fractionally inclined, replace 1.8 with 5/9.

        2. For baking temperatures, it’s close enough to just halve the F numbers in a recipe to get C. 350 F ~ 175 C, 400 F ~ 200 C. I’ve never needed to figure out the conversion to British ‘gas marks’. Or ‘cone number’ for that matter.

        3. ROFLMA!

          The drums are larger than 200 Liters, 45 Imperial Gallons or 55 US Liquid Gallons approx, these measures are different in volume so depending on what unit is used, you get different quantities of “free” air in the drum along with the liquid, let’s not go to units of air. The US itself has different measures for “Gallon” there has been a number of aircraft that have fallen out of the sky with no remaining fuel because of this. These drums were first used for US oil so the most correct volume (by whatever unit) should be 55 US Liquid Gallons.

          The mistake that was made was to use 55 British (Imperial) Gallons (250 Liters) instead of 55 US Liquid Gallons (200 liters). Oh, by the way Britain and the UK are metric now and call them 200 Liter drums.

          It’s 5, 200 Liter drums or 1000 Liters which is one (Metric) Ton not one imperial Tonne.

          A pound is approx 0.454 kg or 454 grams not 0.5 kg

          And! When you mentioned specific heat capacity in a unit I had never heard of – “kilopondmeters per fluid oz”

          Well that’s when I hit the floor laughing. What’s next? “wonky leg walking yards”, “swollen thumb square inches”

          How the hell did you Americans ever get a man to the moon.

          I hope you can see the humor in this for an outsider. I’m not having a dig at you but really “kilopondmeters per fluid oz”, who makes this stuff up?

        4. For “in your head” temp conversions, for C to F, just add 15 and multiply by 2. F to C is divide by two and subtract 15. Yes, it’s not perfect but it’ll be within a couple of degrees if you’re talking about weather.

      2. Foiled by HaD commenters universally mistakenly calling the American system of common weights and measures “Imperial”. Just call it the ANSI system or something similar that we are familiar with to designate the British Empire versus regions influence by the USA. The easiest way to make a guess is do they have 50Hz or 60Hz electric power.

        I am suspect feigned difficulty when I see the complaints. How can so many commenters be experts in everything but can’t estimate between various metrics? Is this one (of the many) hacker versions of virtue signaling?

        1. No, there’s no virtue signalling involved, it really is baffling to many of us.

          Engineers and hackers in the US grow up used to doing fraction arithmetic in their head for trivial measurements (how long is half of 1’ 3/8” again?), and with converting the “customary units” used in their non-nerd lives to and from “engineering units” used in their nerdy lives.

          Here outside the US, we’re used to dealing with just one pretty much self-consistent measurement system. I have to do “customary unit” conversions rare enough that I honestly never can remember the conversion factors beyond 1”=25.4mm, 3’~1m and “0F=Winter in Minnesota, 100F=Fever “. No idea how much a gallon is, just that it’s a lot more than a liter. And I was really surprised to learn there’s more than one type of gallon! What? Why?

          So I just resort to Google for this… And I’m a guy that knows there’s 86400s in a day and crap like that.

          I’m grateful whenever a US nerd thinks of including both units, and smile when they remember to also adjust the significant digits, ie “about 30 feet” becomes “about 30 feet or 10m” instead of “about 30 feet (9.14m)”.

          1. Yeah, right.

            Thing is, for many non US nerds, “customary units” are just … weird. Most of the time they don’t run across them, so they don’t even notice the weirdness. When they do, some comment, even though it’s kinda pointless.

            For most US nerds converting to and from customary units is secondary nature. Many still realise the weirdness and provide both when an international audience may be listening. Most just ignore comments about the weirdness, but for some it becomes a point of pride or something. Flamewars ensue.

            While some comments may be just trolling to get a flamewar going or to virtue signal to themselves how clever they are, I think most comments are bona fide baffled. (Seriously: Two types of gallons? I was in the US, and I was in the UK, and I never realised that, you have to admit that is weird and baffling. But I guess I’ve learned something today!)

            Nuff said.

          2. Not too long ago, our neighbors in Ontario priced their gas in Canuck dollars per Imperial gallon. Figuring out what the differential was hurt my brain. Now it’s loonies per liter, so lots easier.

          3. It’s a big world. I use the metric system most of the time but don’t mind switching around based on units used in the data or documents I’m using. (we should capitalize Metric or something to make it stand out. These are all metrics or metric systems. The one based on the meter and factors of 10 was called the French metric. Saying “the metric system” is very ambiguous. Why not just say SI since that has “system” built in?)

            If I’m looking at old survey data why turn the rods and townships and king’s acres and furlongs into meters? Most of these have values that are powers of 2 or powers of 2 times 10 or 6. Though I am not crazy about pounds and slugs for forces and masses. And is it a mystery why gold prospectors uses ounces and grams. Maybe because a kg is way too big a jump. A gram of gold is about $60 and a kg is $60,000. Does anyone use a mass that is comfortably in between?

            In the last 30 years or so I have noticed the cm has lost its mojo in favor of using 100’s of mm to describe lengths up to several meters. I wonder why? Maybe it goes along with the trend of tour (too-er) becoming tor in videos and advertising. Hmm. That might be the decline of German influence on English. And I hear a lot of pronouncing the ‘t’ in often. Valley Girl influence is rising? Is it just the natural drift in language and style? When I first started college the “metric” system in physics was cgs – centimeter gram second. Force was in dynes and wavelength was angstroms (1nm/10) and was fading fast.

    2. Or, in American units, a human heater is about 500 BTU/hr.
      275 (US) gallons = 2200 lbs
      x 10F = 22000 BTU storage capacity.
      or 44 hrs.

      Seems an American puts out less heat (500 BTU/hr) than the 200 W previously quoted.

      (Disclaimer: Not American, I come from a place where those barrels were always called “45 gallon” size. We just figured the American barrels were bigger, because everything is bigger in America. But no, they just redefined the gallon to make it *seem* bigger.)

      1. Now I’m laughing so hard that I have tears in my eyes …
        Quote:”Or, in American units, a human heater is about 500 BTU/hr”

        hmmm what was BTU again! Oh! British Thermal Units.

        And as for “Seems an American puts out less heat (500 BTU/hr) than the 200 W previously quoted” … well you know – Mackas – Many Americans are becoming better “insulated” now.

        Oh yeah there was a aircraft that fell out of the air for that reason to. A standard measurement was used as an “average” mass (weight) per person. It was one of those small twin turboprop aircraft that are used in the US for short trips.

      1. Not that is has to – in places where you need cooling during the summer, there’s not many days of the year with more than 36 hours between the nights, and as far as I understand the system it’s basically meant to keep a room closer to outside nightside temperature. (But this assumes very unamerican style of isolation on the building itself).

    3. You could put a heat pump between the barrels and the outside heatsink to make this work in warmer or colder climates. Heat the barrels up to 30C overnight with cheap electricity, use that heat indoors over the course of a day. I don’t know of a cheap source of water to water heat pumps though.

      1. You could run an independent water to water-storage circuit with an air-water (pool) heat pump, which are fairly obtainable. It wouldn’t necessarily be cheaper than a conventional split sytem air conditioner (air-air units are more available and cheaper), but the thermal storage still might be beneficial for storing excess or cheap energy via the heat pump.

        1. A Watt is power, a Joule is energy, Energy X time is Power. So Watts X time is energy to but Watts / time is not. Units of energy – Joule, Amp Hours, Watt Hours and it follows – Watt Seconds. A Newton Meter is force.

          1. Energy x time is NOT power. It’s a nonsensical unit.
            “Amp Hours” is NOT a unit of energy. It’s charge, equal to 3600 coulombs.
            A “Newton Meter” is NOT a unit of force. It’s either energy (A joule, by definition) or torque, depending on the direction.
            It’s a crying shame HaD doesn’t let you come back and edit your errors after you sober up.

    4. Similary, you can keep your greenhouse warmer in the winter with some of these barrels of water. Just paint them black and place them where they can absorb lots of sunlight/heat. When it cools down at night , they will radiate heat for a good while.

        1. What a fascinating definition of garbage you have! Even if the projector wasn’t functional it would have been more useful to someone as parts. Literally any box of a big enough size would work just as well as an enclosure for the controller, without the need for ‘reappropriating’ something so specialised. Surely this justifies a bit of complaint.

      1. I can’t speak for schools internationally… but I think my primary school (which first got computers in the classroom back in 1992… Apple IIe’s which I think came out of someone’s garage), did have one 16mm projector which I encountered exactly once.

        If we were going to see anything, the technology of the day was VHS tape: played on a trolley-mounted small combined CRT television/cassette player which had maybe a 15″ or so screen on it.

        So I’d be very surprised if they were still in schools, given 30 years ago, they were considered obsolete at least here in Australia.

        These are no longer manufactured, and there is much content that exists on 8mm film that is not easily available on other formats. There’s also the pleasure of watching a film from its native media. (No different to those who choose to listen to records instead of CDs for that matter.)

        It just seems that this project was shoehorned inside this projector because it was “laying around” and could be made to fit. No word on whether it was functional prior to this surgery (I have YouTube blocked so can’t comment on the video content), but this does not matter now as it likely isn’t post-surgery.

        I think there could have been more appropriate enclosures used that wouldn’t have seen the senseless destruction of a historic media playback device.

    1. The power consumption is negligible compared to an Air Conditioner. A small electric water pump consumes in the order of watts, perhaps 10’s of watts and a AC compressor consumes in the order of kilowatts.

      The drums are working as both thermal storage and also dissipating heat into the ground. The don’t do the latter very well due to the low surface area to volume ratio but it’s still an efficiency improvement. Pipes are better for this.

        1. 1500W is on the order of kilowatts isn’t it? And it is easy to have a 20 amp socket and breaker if you need it.

          Or do like Carl Sagan and say “Tens of watts!” which covers 20 watts to infinity. He really liked that broad coverage when wowing the rubes on The Tonight Show. Tens of thousands of asteroids! Tens of stellar masses! Tens of millions of light years! It is really hard to be wrong and you can claim you correctly predicted so many things :-)

    1. Deeper is also naturally cooler – I’ve seen systems that don’t bother with the outside radiator & fan, since if you’re down more than a few feet (or, oh, I don’t know, a meter or so?), the temp is pretty constant and also has immense heat capacity (sorry, I don’t have the numbers), so you don’t even need that much water storage. And that constant temperature is also useful for heating in the winter.

      1. Practically: yes…Technically: It’s cooler right up until it’s not (but no one is digging a few hundred meters down in their back yard to have to worry about that either)

      1. That depends on the span of “each year”. The average is 3 days per year. One heat wave of 8 or 10 days really blows up the apparent trends feeds confirmation bias with every news source. And it seems to me that a few years ago there were a coupe years in a row with no summery hot days.

  2. Interesting, might fit my needs in WNY for a workshop.
    However, first thing I’d do is get some sort of anti-freeze in there for burst protection. Second thing would be to go a few feet deeper, frost-line would be 50-60″, to far, but still cooler in summer. Would have to consider a couple of 100′ rolls of PEX as a ground loop at the beginning of the string, as it would expose more surface area to the ground vs those drums.

    1. Ideally thermal storage should be thermally isolated except for when it is beneficial for it to be thermally conductive.

      The normal approach is drums for storage and pipes for conductivity. Drums don’t have a high surface area to volume ratio like pipes.

      I wonder though about a drum within a drum where the inner drum is storage and the gap between can be filled with water for conductivity or filled with air for insulation.

  3. How about to use a swimming pool as heath sink?
    Guess the cooling down at night might be the difficulty?
    Not yet a serious issue yet in Sweden but it getting hotter in summer.

    1. Cooling down at night generally isn’t a difficulty. Our 6 m x 12 m pool would lose 500 kWh of heat on a cool, clear night if we forgot to put the blanket on. It’s almost all evaporative loss: about a cubic meter.

      In a cloudy, humid city, loss would be much less though.

    2. “How about to use a swimming pool as heath sink?”

      I think a Heath bar will sink in a swimming pool.
      But what does that have to do with cooling a work shed?

  4. I’ve been considering making a summer/winter system, with solar heat collectors for winter. I live in a mild climate (NC, USA). Was looking at NaOH literally last night. And thinking about how to make that a normal loop and a modular thing where I store 5 gallon bags maybe. And then how to use a similar system with some rerouting for summer.. I had a mid 70’s F week (highs) last week, but will be heading into a cooler week, and I’m looking for ways to smooth the peaks. I’m planning on a split system as a replacement for a 2nd hvac, but after seeing a tech. ingredience thought that could work well for me. I might would still consider some loops for heat exchange when needed.

    And I do have a PV system, but live in a valley so it’s not as optimal as desired…

    btw I do work in power… but I’m a structural foundations guy. I do mostly know how everything else works, took thermodynamics etc… but not part of my day job…

    I was thinking of trying to run a loop behind solar panels to cool in summer, only I don’t have a great cool sink, and don’t need that much hot water.

    Unless I buy an unreasonable number of Seabek/ Peltier junctions. Again not efficient.

    So any tips? And sorry for misspellings etc…

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