Homebrewed Electricity > Other
Ever built a steam engine?
Astro:
Ok so, my ac unit is a 2.5 ton and should be a 3 ton. It was made in 2002. I get that it needs updating.
But to go from a 12 seer 2.5 ton to a 3 ton 18 seer, is going to cost around a minimum of $3000.
Sticking to my 5 year payback rule I would need to save $200 a month in the summer months. Ac runs about 3 months and 6 weeks at it's hardest. 5 years 3 months a year, 15 months. $3000 divided by 15 months. So $200 a month.
So the question is (and this is where I like engineers and people that like math) do the calculations warrant the upgrade?
Running some simple numbers, if a new 18 seer 3 ton cut my ac bill in half (idk if it would do that, I doubt it, again I am not going to do the math) I would save $125 a month (given what price I pay on avg for kwh), during those 3 months. SO $375 a year savings on a $3000 investment. OR an 8 year payback. SO that does not fit into my 5 year rule.
I know that going up in seer helps, but the cost also goes up.
At that rate I would be better of spend the $3000 on a stand alone ac unit that hooks directly up to solar panels. One set up would not be enough to cool the house, but the pay back is 100% of everything it puts out.
Same with building a turbine.
Mary B:
A central AC unit is going to last 10+ years... you need to calculate use cost over lifespan to make a decision...New one is going to use a lot less electricity too so calculate that in.
Astro:
--- Quote from: Mary B on October 09, 2021, 01:33:44 PM ---A central AC unit is going to last 10+ years... you need to calculate use cost over lifespan to make a decision...New one is going to use a lot less electricity too so calculate that in.
--- End quote ---
They are not guaranteed to last that long. They usually do though. I worked in an industry that by the time we ramped up to production from concept to protype, it was already outdated. We already had working prototypes for the next generation before we had ramped up production on the previous version.
They say "if your ac unit is 10 years old or older it should be updated" due to energy advancements.
I did calculate the pay back time and depending on how hot the summers are it is going to take 8 years if they are the way they were this year. (it was a pretty warm summer). But it could take 10-11 years and it could take 7 years. Any less then 7 and the heat is going to be the last thing to worry about, because everything would begin to collapse if the summer was that hot.
So figure 8-9 years. That payback sucks and is not good enough. There are better ways.
joestue:
Take your 2.5 ton system and figure out if its running properly. My guess is it isn't. Maybe the txv needs adjustment, maybe it needs a new one, maybe it needs more or less air flow through the coil to deliver the cooling capacity and dehumidification you need.
anyhow, if that's not good enough, find yourself a 5hp vfd and run the compressor off the vfd. run it up to 75Hz if you like. or down to about 45hz. no need to install a bigger system just to pull more water out of the air, or get a shorter run time because it can't quite keep up.
if you're in the usa i can help you out with the transformer selection needed to transform 3 phase from the vfd into the proper 2 phase voltage that a standard capacitor run compressor motor needs. its not a particularly high kva requirement.
a 5 ton 240v system will need a 240v to 120v transformer rated for 6 amps, and you will need a 240v to 16/32v transformer to "add" 16 or 32 volts to the second phase to make more current flow through the "start" winding.
the compressor will self start even with head pressure, if you program the vfd properly. if not, you will need to preserve the standard 5 minute delay between restarts which is standard for most all hvac heat pumps.
getting the hvac system to control the vfd is very easy. just use the contactor that previously provided 240v to the compressor, to instead close the circuit to turn the vfd on.
to get a higher seer rating, keep the 2.5 ton compressor and plumb in a bigger condenser. 20 pound propane bottles can safely be used to hold r-410 provided you hydrotest the tank to 400 pounds and you keep it cool while recovering the refridgerant.
a compressor from a refridgerator can be used to suck it all out of your system.
you can flow propane instead of nitrogen through your system while brazing the tubes together. (no need for a regulator and propane or argon bottle). and.. to be honest, there is a 8% silver solder that melts at like 500F that is just fine for R-410 systems. it has a high enough fatigue limit it wont fail. (r-22 could be used with regular soft solder)
old fans are horribly inefficient. a 1/3rd hp induction motor sucking up 200 to 300 watts will move as much air with a stamped sheet metal fan blade, as a 60 watt inverter fan motor with its aerodynamically designed plastic injection molded fan blade.
i have not had good success driving pmdc motors with 60-80$ chinease 2hp vfds, due to unreliable startup.
but you can buy a legit vfd from automation direct or elsewhere and they now have the capacity to drive synchronous motors properly. the 250$ spent is.. actually less than the pmdc inverter fan motors that are now installed in 18 seer hvac systems. go to the dumpster behind an hvac shop and find a junked motor. change the bearings, epoxy the magnets back on, it will work again.
question being, is your time worth it.
Astro:
--- Quote from: joestue on October 10, 2021, 11:45:29 PM ---Take your 2.5 ton system and figure out if its running properly. My guess is it isn't. Maybe the txv needs adjustment, maybe it needs a new one, maybe it needs more or less air flow through the coil to deliver the cooling capacity and dehumidification you need.
anyhow, if that's not good enough, find yourself a 5hp vfd and run the compressor off the vfd. run it up to 75Hz if you like. or down to about 45hz. no need to install a bigger system just to pull more water out of the air, or get a shorter run time because it can't quite keep up.
if you're in the usa i can help you out with the transformer selection needed to transform 3 phase from the vfd into the proper 2 phase voltage that a standard capacitor run compressor motor needs. its not a particularly high kva requirement.
a 5 ton 240v system will need a 240v to 120v transformer rated for 6 amps, and you will need a 240v to 16/32v transformer to "add" 16 or 32 volts to the second phase to make more current flow through the "start" winding.
the compressor will self start even with head pressure, if you program the vfd properly. if not, you will need to preserve the standard 5 minute delay between restarts which is standard for most all hvac heat pumps.
getting the hvac system to control the vfd is very easy. just use the contactor that previously provided 240v to the compressor, to instead close the circuit to turn the vfd on.
to get a higher seer rating, keep the 2.5 ton compressor and plumb in a bigger condenser. 20 pound propane bottles can safely be used to hold r-410 provided you hydrotest the tank to 400 pounds and you keep it cool while recovering the refridgerant.
a compressor from a refridgerator can be used to suck it all out of your system.
you can flow propane instead of nitrogen through your system while brazing the tubes together. (no need for a regulator and propane or argon bottle). and.. to be honest, there is a 8% silver solder that melts at like 500F that is just fine for R-410 systems. it has a high enough fatigue limit it wont fail. (r-22 could be used with regular soft solder)
old fans are horribly inefficient. a 1/3rd hp induction motor sucking up 200 to 300 watts will move as much air with a stamped sheet metal fan blade, as a 60 watt inverter fan motor with its aerodynamically designed plastic injection molded fan blade.
i have not had good success driving pmdc motors with 60-80$ chinease 2hp vfds, due to unreliable startup.
but you can buy a legit vfd from automation direct or elsewhere and they now have the capacity to drive synchronous motors properly. the 250$ spent is.. actually less than the pmdc inverter fan motors that are now installed in 18 seer hvac systems. go to the dumpster behind an hvac shop and find a junked motor. change the bearings, epoxy the magnets back on, it will work again.
question being, is your time worth it.
--- End quote ---
I like the way you think.
I am pretty familiar with vfd's. Never thought of that idea. Also it never dawned on me to swap the fan for a more efficient one.
I know it will eventually need replaced. Maybe in the next 5 years or so, so I do not want to spend a ton on it.
I am gradually getting the place fixed up and while we do have an "emergency" fund for big ticket items, I am not the type to waste money getting a new one, when this one works and the pay back on a new one does not come close to what I think it should.
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