Announcement

Collapse
No announcement yet.

Doghouse Air Conditioner for Solar Shed: Separate Inverter to Run It?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Doghouse Air Conditioner for Solar Shed: Separate Inverter to Run It?

    My charge controllers, Outback Radian GS8048 inverter, and AGM batteries are housed inside a dedicated plywood and sheet metal equipment shed:
    IMG_2706.jpg


    Down at the bottom left there is an air intake vent, and the exhaust vents run along the top just above the doors. At the moment, I'm relying on passive convection for cooling, which works fine most of the year. But it's starting to get warm here in Eastern Washington and I'm going to need to actively cool the interior of the shed unless I want the electrolytic capacitors going bad in my charge controllers and inverter after a couple of summers. Right now, at 80 degrees F outside and with the inverter producing 5 kW, it's about 94 degrees F inside the shed and will probably reach 100 degrees by this afternoon. (The hundreds of pounds of equipment and plywood, and the thousand pounds of battery, have considerable heat capacity and it takes a while to warm up in there.)

    So, I'm planning to buy a 2,500 BTU Mini Portable Heater and Air Conditioner available from ClimateRight for $450. It's intended for dog houses but should work perfectly for my purpose. The AC compressor consumes 480W. The 730W of cooling capacity is just about a match for the waste heat produced by the Outback Radian running full tilt. Together, the charge controllers add another 200W or so in power dissipation, so the AC unit wouldn't quite be able to keep up, but it would at least reduce the temperature inside.

    My question is whether I should power this thing from the Outback Radian inverter or hook up a dedicated off-grid inverter to the battery and power it with that. I'd prefer to not have my cooling system add another AC load to the very device I'm trying to keep cool, and a Cotek SP1000-148 inverter rated at 1000W continuous is relatively cheap (compared to everything else in this shed) at $350. It supposedly can put out 1750 VA for up to a second, which should be plenty enough to start the compressor.

    One thing that makes me a little uncomfortable about the Cotek inverter is that it has a GFCI outlet and probably a floating neutral. But is that really an issue for powering a single specialized load outside, not connected to the house wiring at all?

    There are two mounting options I see. If I housed the Cotek inverter inside the shed, I'd need to put a plug on one end of a 120V 3-wire cable and connect the other end to an in-use outdoor power receptacle mounted on the shed wall. As an alternative, I could put a hole in the shed wall just big enough for the AC unit's power plug to fit through, and plug in the AC unit directly to the inverter. In either case, I'd connect the Cotek inverter ground to the EGC busbar inside the Outback's load center, which then goes through conduit to eventually wind up at the house's GEC.

    Any thoughts on this?
    Last edited by BackwoodsEE; 05-22-2018, 03:58 PM.

  • #2
    I'd really consider forced air as a much less power intensive cooling solution. Especially in Eastern Washington which is relatively mild. Consider what's the max temp you're willing to let things run at. 104F is 40C, which is more than friendly for Electrolytic Caps (typical rating of 85C (185F) or higher.) 104F is getting up there for Lead batteries, but still not really all that high.

    Max temp in Spokane any given summer might get to 100F (Over the past century you can count on your hands the total number of days that the temp has exceed 101F.)

    Pulling in this air, and directing it over components would be an effective way of keeping the temps down overall, and static air temp down below outside + ~3F. Have it kick on at about 90/95F and consume a lot less electricity. What's that space size 200 cubic feet? A 1/8hp exhaust fan at 50W pushing 680cfm would pull through >3x the amount of air that the space has every minute.

    You're not trying to keep a dog cool, you're trying to keep you equipment in good working order.

    Comment


    • #3
      Originally posted by TAZ427 View Post
      I'd really consider forced air as a much less power intensive cooling solution. Especially in Eastern Washington which is relatively mild. Consider what's the max temp you're willing to let things run at. 104F is 40C, which is more than friendly for Electrolytic Caps (typical rating of 85C (185F) or higher.) 104F is getting up there for Lead batteries, but still not really all that high.

      Max temp in Spokane any given summer might get to 100F (Over the past century you can count on your hands the total number of days that the temp has exceed 101F.)

      Pulling in this air, and directing it over components would be an effective way of keeping the temps down overall, and static air temp down below outside + ~3F. Have it kick on at about 90/95F and consume a lot less electricity. What's that space size 200 cubic feet? A 1/8hp exhaust fan at 50W pushing 680cfm would pull through >3x the amount of air that the space has every minute.

      You're not trying to keep a dog cool, you're trying to keep you equipment in good working order.
      Interesting thoughts, thanks! Well worth considering. Certainly a lot simpler and cheaper to blow air than cool it.

      The batteries tend to stay a little cooler because they're resting on the concrete slab. At full power, the capacitors run about 7-10C hotter than ambient, so an internal shed temp of 40C would let them stay below 50C.

      Arrhenius's law says the capacitor lifetime doubles with each 10C reduction in temperature. Given that the caps are typically rated for 2000 hours of operation at 85C, I could expect 16,000 hours at 55C and 32,000 hours at 45C. Say the equipment cranks away for 10 hours per day with caps at elevated temps each summer, that would be, 10 hrs x 30 days x 2 months = 600 hours. I guess that would be OK if the caps don't exceed 55C, but I'd definitely be cutting into the equipment life at much higher temps.

      P.S. Unfortunately, those stats about 101F maximums here are a thing of the past century, not this one. We routinely get temps that hot now each summer, and much of each August is in the 90s.

      Comment


      • #4
        I'd suggest a little experiment. Take a small fan, put it in there now, just to blow on the capacitors. Now measure the air temp vs cap temp (after say 10-15min of blowing.) You'll see that 7-10C delta between air and cap temp drop a good amount as well. That's why processors don't just have a heat sink but have a fan as well for thermal dissipation.

        Comment


        • #5
          The capacitors are not doing anything helpful. Why would you want to waste so much energy for something you do not need especially when that power coming from solar cost you 4 to 8 times more than buying it.

          But I do have another idea, and it does not use electricity. Ever thought about one of these Whirly Birds. Draw air from the bottom you already have up and out.

          Last edited by Sunking; 05-22-2018, 09:15 PM.
          MSEE, PE

          Comment


          • #6
            Built correctly caps can help you "ride through" momentary power dips.

            As for why the OP has built that system, you have to go back to some of his original posts to see what and why he built it.

            I do like his Faraday cage around his system hardware.

            Comment


            • #7
              Originally posted by SunEagle View Post
              As for why the OP has built that system, you have to go back to some of his original posts to see what and why he built it.
              I know, micro-cyles a non issue IMO.

              MSEE, PE

              Comment


              • #8
                Ditto on the forced air, put a squirrel cage blower inside that intake vent, and pressurize the shed. or 2 of them, that 4" vent isnt very much. And put some insulation on the inner walls, so it's not a bake oven from the hot sheet metal. Let it run all night and cool the interior down too.
                Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                solar: http://tinyurl.com/LMR-Solar
                gen: http://tinyurl.com/LMR-Lister

                Comment


                • #9
                  Originally posted by Sunking View Post
                  The capacitors are not doing anything helpful. Why would you want to waste so much energy for something you do not need especially when that power coming from solar cost you 4 to 8 times more than buying it.
                  The capacitors I'm concerned about are the ones inside the charge controllers and the Outback radian inverter.

                  Comment


                  • #10
                    Originally posted by BackwoodsEE View Post
                    The capacitors I'm concerned about are the ones inside the charge controllers and the Outback radian inverter.
                    Ironic huh? Being off-grid using equipment that cannot withstand local climates and heat forcing you to wast energy to to keep the equipment cool. Seems to be a flaw somewhere in the logic. Sort of like Thin Film panels where sunlight destroys them.
                    MSEE, PE

                    Comment


                    • #11
                      Originally posted by Sunking View Post
                      Ironic huh? Being off-grid using equipment that cannot withstand local climates and heat forcing you to wast energy to to keep the equipment cool. Seems to be a flaw somewhere in the logic. Sort of like Thin Film panels where sunlight destroys them.
                      Yeah. The electrolytic capacitor is the Achilles heel of solar equipment. Everything else, including decent PV panels, will last for decades. But invisible wisps of electrolyte are vaporizing in those caps even as I write this, and they'll fail in ten years if I don't baby them.

                      I've thought of asking Outback and Morningstar if they will tell me what electrolytic caps they use in the devices so I can order replacements from Digi-Key, just in case, and put them in the basement with some series 9V batteries hooked up to maintain a formation DC charge on them. Or I might just look online for someone who's done a tear-down. There are probably no more than $200 (retail) worth of electrolytic capacitors that will eventually bring down this equipment totaling more than $6000 retail.

                      Comment


                      • #12
                        My gear is almost 12 years old the two PWM CC have only passive cooling, the inverter has 2 stage fan, with no failure (yet)

                        I live in a wet tropics area. 5 meters average rainfall and daytime time average around 30c so its hot and humid a lot.

                        I also think A/C is overkill and not cost effective. I agree with a fan on the inlet and you could also put a small DC PC fan under each unit and blow air up it.

                        And either grow some trees over the shed or cover it with shade cloth, you have built a solar oven.

                        Comment


                        • #13
                          Another option you may look at is a small evaporative cooler.

                          When it gets hot in Eastern WA it is usually quiet dry and swamp coolers work reasonably well.

                          https://www.turbokool.net

                          Comment


                          • #14
                            Originally posted by PNW_Steve View Post
                            Another option you may look at is a small evaporative cooler......
                            I'd suggest not, because of the excess humidity causing sneak leakage paths and increasing corrosion overall.

                            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                            solar: http://tinyurl.com/LMR-Solar
                            gen: http://tinyurl.com/LMR-Lister

                            Comment

                            Working...
                            X