Quote:
It's a hypothetical situation that I don't have, but is all too common.
1.)Let's say the unit is maybe 4 years old and the company who installed it is still in business just like many "hack" HVAC companies.
2.)This is a DIY site and electrical stuff is generally more within reach of the average DIYer than refrigerant plumbing.
3.) In most areas (at least in the US), it is not necessary to have an electrician license to work on the wiring in your own house - how does Home Depot sell so many electrical parts to the general public?
4.) There is a heat pump out there that runs on a VFD just fine. It was a R22 unit converted to run on R134a, so I figure it must have been really oversized to begin with.
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1.) Option 5 here. It's not terribly old. Perhaps one of the salesman made less than wise decision. If you're a great negotiator and well versed in self representation, you maybe able to compel them to correct the sizing by establishing that sizing was incorrect at the time of install and that it was merely a delayed discovery of defect in workmanship of selection. You just hire someone to do proper sizing, then have a legal expert write them a letter requesting resolution and accomplish a resolution for lesser monetary $$ than VFD + permit cost.
2.) That's a presumption based on assuming what's easy to you is easy to everyone. The breadth of reach is contingent upon the skills, experience, comfort level and tools available for use to the individual(s). Your dPIC, DSP program codes posts are beyond comprehension to many DIYers. For some DIYers, all this digital bullcrap is extremely labor and resource intensive (computer stuff, wires, interfaces, soldering, software)
3.) I said that in SOME. Which jurisdictions have you verified to come to your conclusion it is allowed in most places in the US? At least around here, homeowners may do some work, but still require permit and inspections and the AHJ may or may not pass inspection on jury rigged modification to permanently installed equipment. Availability of materials at Home Depot/Lowe's is not an assumption of legality and "buy it and do whatever you want". You can buy bath tubs, sinks and such that requires plumbing permit to install as well as black iron pipes mainly used for gas piping, which may or may not be legal to DIY depending on your locale. Furthermore, your AHJ may not pass improper or butchered install.
4.). Ok great. An existence of a working unit doesn't mean absence of problem in every install. Look up return gas velocity. How far you can push the envelope before problem develops depends on the system.
Reducing compressor reduces return gas velocity and on systems with not much room for loss in return gas velocity before oil return issues. In this case compress damage wouldn't be covered by warranty.
How far, and how long you can operate under reduced speed is system dependent. So, if your over sized unit is used like a mini-split and it runs basically around the clock between 10-20% capacity, you might actually be losing oil from compressor.
From Copeland Emerson Climate AE-1495
"
Piping
Unlike a variable speed compressor whose
mass flow
and gas velocity changes with its speed, the digital
scroll’s pumping capacity is equal to its 100% capacity
while it is pumping. For this reason the gas velocity
remains high even during periods when the capacity
demand is low. Because the mass flow and gas velocity
remain high, piping may be designed as if it were
designed for a non capacity controlled compressor. For
vertical piping a trap every 20 feet should be sufficient
to ensure proper oil return. This recommendation is
based upon a minimum 1500 fpm velocity or higher.
When the digital scroll compressor is part of a tandem,
a double riser should be considered to assure that the
velocity remains above 1500 fpm when only the digital
scroll is running.
Start Up and Shut Down
To improve the starting characteristics of the digital
scroll compressor, the the Emerson controllers delay
loading the compressor for 0.1 seconds. Likewise, to
eliminate the reverse rotation sound at shut down the
compressor is unloaded 0.5 seconds before shut down.
Compressor Cycling
Because of the
digital scroll's seamless capacity
modulation from 10% to 100%, capacity short cycling
should not be a problem for single compressors.
However, if the digital compressor is in tandem with a
non modulated scroll, short cycling of the non modulated
compressor may be a problem if the system control is
not designed and set correctly. The Emerson digital
controllers have a built in two minute anti-short cycle
timer to prevent short cycling."