Quote:
Originally Posted by jeff5may
Take a look at the new PTAC units and mini-split units that have come out recently. I believe these are a 4th or 5th generation, heat pump centered set of units. Many of the issues with energy wasting, whooshing sounds, ticking, clicking, being impossible to program, low ambient suffering,and such have been dealt with quite well. A decent portion of these units have electric expansion valves and big outdoor heat exchangers in them.
Lots of them have separate functions for different needs/goals. COP in heating between 3 and 5 down to 20 degrees F. Cold-buster hyper-heat turbo-blast function that spins inverter at 120% rpms and bypass pulses the evap coil with hot fog for more mass flow. Blow lots of 80 degree air at high efficiency. Don't blow air until the hx is above 90 degrees to avoid 80 degree airblow. Control it from your iphone at will. These units have come a long way in a short time.
That being said, expecting full capacity out of any ashp unit below about 25F is going to cost you energy. Either the electric meter runs faster or the heat doesn't come in very warm. The only way around that is a ground source that stays not cold all year long.
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I'm using the latest gen Fujitsu model which has all of those features.
It doesn't blow until the heat exchanger warms up, but you still get a cool breeze during defrost (the fan runs at low speed) and no hot air which during a -2 degree outside temp and a long defrost of 5 minutes, you feel it. In fact the fan always runs at low speed.
The pop and crackle of the metal exchanger is typical of most systems, and it's no better or worse. BIg ol radiators and resistive electric wall mounts are not as common in serious winter areas so the noise is something new to get use to.
The issue is the typical wall unit is a large plastic case snapped together. In mild heating needs it's probably not that bad, but during deeper cold spells the dramatic swings in heat output back to long defrost and such really makes the thing crackle. You can simulate it by just holding the unit (when not installed) and twisting it with your hands.
This is a problem for very few, so it's not likely to see effort.
Personally I have doctored my unit in various attempts to quite it, adding buffer velvet to certain rubbing spots, etc.
The energy wasting I was mentioning comes with the outdoor pan heating element at the bottom of the unit. Defrost water collects and freezes there, and plugs the drain holes rather quickly. There is no 'smart' system of detecting such and only defrosting during that time, so the outdoor pan heater runs constantly at temps below 30 degrees, at 120watts which can be all day and night for a couple months during most real winters.
I've tried doctoring my own defrost strip using only 30watts, that runs on a timer, and i only plug it in when I start to see constant under 20degree temps.
There is a cold buster powerful mode, and it does work, but it throws the unit that much more quickly into defrost mode in deep cold so it has it's drawback too, unlike the powerful mode for cooling which you can keep pressing and runs continuously. Plus it sucks the watts obviously.
I think it's darn impressive that it can suck heat out of a 18 degree night like right now, and especially a -15 degree night. The reality is while they have been designed to work down to those extreme temps, they are not designed to operate long in them, so for cost efficiency will lack some necessary functions.
A simple resistive heating element strip that came on during startup or defrost cycles would help with the chills. The pan needs a smart rapid defrost.