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OK, HVAC thread, I've got a request. I'm buying a house and the AC is 21 years old. It still blows cold, but it's obviously on its last legs and I should be lucky it hasn't disintegrated yet. The house is ~2100sqft, with vaulted ceilings in 1600 of it. Ideally, I'd like to get a full commercial-style system going, with outdoor air intake, balancing dampers, multizone with a thermostat in each bedroom and one for the livingroom/kitchen area, etc. Are these things made in non-rooftop unit form factors for residential use? If so, where do I start looking? If not, is there a way to get a system to work this way? I like the idea of being able to pull in nice, cool outside air, but don't want to have to deal with all the dirt and bugs that opening windows entails. What about humidification/dehumidification? I've got a pretty big closet for the air handler right now, so volume likely isn't a concern. Anything else I need to look out for?
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Aug 22, 2016 01:07
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| # ¿ May 5, 2024 15:09 |
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Ok, so I crawled around under the house and there's just square duct screwed to the joists above the insulation and vapor barrier. In a couple of spots, the vapor barrier is torn, so humid under-house air is condensing on the ducts, dripping off, and filling the insulation with water. So I think all new insulated ducting is in order. Everything's currently run with baseboard registers. I still want to do a multi-zone system. Do I need return registers for every zone? Currently, the air handler just pulls air in through the closet door, and that's the return for the whole house. There's a ton of room under the house. Would it be a good option to try to put a VAV in for each zone I'm setting up? I can use a central air handler on a heat pump to deliver constant-temperature air at a specific flow rate and just ramp the flow rate up or down depending zone demand, right? I still want to get some exterior makeup air for the main living space, and it looks like an "economizer" damper is easy to install in my current setup. It looks like we'll only ever need dehumidification, so that should be straightforward enough to set up.
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Sep 3, 2016 02:08
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Bad Munki posted:Is this a good place to ask for help on an emergency HVAC question? Go to where the blower is. Set blower to "on" with the tstat. Spin blower carefully by hand. If blower spins, replace start cap. If motor doesn't spin, you've got other problems. Give make/models of your blower, and describe any noises you hear and lights you see.
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Dec 31, 2017 18:05
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ExplodingSims posted:Yup. ECM. Those are pretty expensive when they fail. The good news is is that a aftermarket rescue Motors are pretty much the same now. I would like to know more about these "ECM" units. Brushless DC or something?
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Jan 1, 2018 16:52
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Just popping into this thread to say that HVACDirect.com has grotesquely exceeded my expectations in every way. I ended up buying a 42,000 BTU Mitsubishi multi-unit mini-split. They have all the documents on the site for download: install manual, maintenance manual, ENGINEERING MANUAL. I was able to assemble a system that fit my needs perfectly. Due to wonkiness with my bank, the payment wouldn't process. I spent an hour on the phone with their accounts department and my bank trying to get it to work (without having to mail a physical check). Ended up splitting the payment into two orders, one for the base system (condenser and all the heads) and one for all the accessories (branch box, linesets, condensate, etc). The next day, I got an email: "hey, on order #xxx, the system you ordered requires a branch box to work. that was not included in the order. if you missed that, please contact me at xxx and we can figure out which one you need!" I sent back "I made two orders, XXX and YYY; hopefully that covers everything, if not, feel free to reach back out." About four hours later "everything looks good, we're boxing it up now." It's like one of those local companies that does all the good stuff, but just so happens to have a nationwide web presence. Not affiliated with them at all, just wanted to say that everything has been beyond what I've come to expect from a major purchase online. I also looked at MrCoolDIY, but they funnel everything through the Lowes or Home Depot storefronts, so parametric searches are what Lowes or HD provides. I also got quotes from local contractors; one of them specced out the EXACT system I had selected (make, model, everything) and was about 25% over cost for equipment, plus another 75% for labor. Theirs was the lowest bid, too. So I ended up getting my system for less than half of quoted installed price after tax and shipping. I'll probably forget to ever come back here to let y'all know how the install goes.
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Apr 20, 2023 22:33
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MRC48B posted:not to deflate you on this, but all of Mitsu (now mitsu/trane) documentation is a public site. I'm aware; it's just refreshing for an online retailer to link ALL the docs directly from the "add to cart" page instead of having to dig through the support menu or type in a model number or something.
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Apr 23, 2023 21:21
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babyeatingpsychopath posted:I'll probably forget to ever come back here to let y'all know how the install goes. Even though I made two orders, everything showed up on one LTL pallet with all items identified. No damage. So far, I'm doing pretty well with unit mounting and running linesets. Just gotta figure out condensate drains. Either I'm using condensate pumps and doing everything in the attic or figuring out how to find the units in the crawlspace and fishing condensate lines through the walls. Any simple calculation for how much condensate is going to be produced, rule of thumb? Like, "x btu at 85% RH and y degree temp drop = z volume condensate/hr" ? I can do dry air calculations based on mass flow rate and stuff, but I'd like to not have to resort to dimensional analysis hell inside a circle of unit conversions. edit: the engineering manual has "moisture removal pt/hr" as one of its line items. babyeatingpsychopath fucked around with this message at 16:44 on Apr 30, 2023 |
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Apr 30, 2023 16:28
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Got all the units installed, and refrigerant and power wiring connected. It took me four days to vacuum down the system. Vacuum pump failed the first day, manifold blew an o-ring the second day. Third day was finding the one leak, and the fourth day was successful vacuum. Vacuumed down to 500micron, purged with dry nitrogen and pressurized (in steps) to 700psi. Did a final leak check. Vac to 500, break vac with nitrogen, vac to 300, nitrogen, vac to 200 and let sit overnight. I left it at 194 and came back to 198, so no vacuum leaks! Called my HVAC buddy to give his blessing and charge the system per EPA rules. He looked over everything and said "looks good, man. if anyone asks, i'll say i did the refrigerant piping. this electrical... that is DEFINITELY your fault" Started doing test runs and discovered that my helper had labelled one of the linesets wrong so the wiring was wrong (since I matched the wiring to the lineset label). That repaired, the system seems to test fine except it's acting like there's not enough refrigerant. Attached photo is from the install manual. I have SM42, and four indoor units: 18, 12, 6, 6. The main unit connects to a branch box and has a liquid line 9.52mm diameter (3/8"). All other units have liquid line 6.35mm diameter (1/4"). Main lineset is 10.6m (35'), all other linesets are 9.1m (30'). My math looks like this: A=10.6 a+b+c+d=9.1 * 4 = 36.4 Total capacity= 18 + 12 + 6 + 6 = 42. 10.6m * 50g/m + 36.4m * 19g/m + 2500g = 530 + 691 + 2500 = 3721g, round to 3.8kg (8.377 lb; 8lb 6oz). My buddy came over with a full 10lb bottle of R-410a and put in 8 lb 6oz. The suction-side pressure was down to 20psi and the discharge pressure didn't get much above 200psi, so he put in the other couple of pounds. Suction side is still in the 50s and discharge is about 210 or so; he said he'll be back with more refrigerant "later."
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May 23, 2023 14:12
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It turns out the branch box cover is labelled "ABCDE" for the pipe connections, but the pipes themselves are labelled "EDCBA"  So the outdoor unit was trying to pump refrigerant into a closed cap or into a coil that had no fan running. It's why the system test ran fine; system test opens all valves and turns on all fans. Now that all the control cables are actually running to the valves they are piped to, the system works GREAT. It's eerily quiet.
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May 24, 2023 12:29
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| # ¿ May 5, 2024 15:09 |
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MRC48B posted:Yeah you can't do this with VRF systems. or even with variable speed mini splits. If you know you calculated the charge correctly, and you weighed in the correct amount, It's not a charge problem. Good point. We did have the system in test mode so it was running flat-out with all units so that we could check the stuff out of the book. I do feel silly for having the piping be EDCB but the wiring landed on the control terminals as ABCD. Every now and again, two units would ask for the same thing and the system would run perfectly... then another unit would call for cool and the compressor would try to dump BTUs into a nonmoving fan and everything would freeze. Since everything was very well wrapped and insulated, it was very hard to diagnose until I decided to get froggy and climb in the attic and just check what all the linesets felt like (and shoot temperatures). Pulling the insulation blanket off, I saw the piping labels and  .
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May 26, 2023 13:53
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