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Re: Share Your Home Electrification/Efficiency Improvements

Posted: Sat Sep 07, 2019 7:28 am
by SageBrush
LeftieBiker wrote:
Fri Sep 06, 2019 6:28 pm
You already know that the heat pump works best when it's nearly loafing
Not so ! It works most efficiently when load is ~ 50% of maximum. That is why it is so important to to size the heat pump correctly: maximum load is inefficient, low load is inefficient. All hypermilers should know this.

Oil-y has "figured out" how to size and run the heat pump in the most inefficient way possible :?

Re: Share Your Home Electrification/Efficiency Improvements

Posted: Sat Sep 07, 2019 8:50 am
by iPlug
I don't know too much about the history of mini split heat pumps. I think Oilpan4 says he had an old fixed speed heat pump. Assuming like central air ones these have come in 2-3 stage and infinitely variable for a while now. There are probably some nice load efficiency charts on these things out there.

Re: Share Your Home Electrification/Efficiency Improvements

Posted: Sat Sep 07, 2019 10:48 am
by SageBrush
iPlug wrote:
Sat Sep 07, 2019 8:50 am
I don't know too much about the history of mini split heat pumps. I think Oilpan4 says he had an old fixed speed heat pump. Assuming like central air ones these have come in 2-3 stage and infinitely variable for a while now. There are probably some nice load efficiency charts on these things out there.
Quite right. The new gen inverter based heat pumps have a much wider range of efficient loads but the advice to size the heat pump for close to continuous operation at moderate load still holds. The old 1-stage pumps would cycle incessantly between off and full load since it was better than running low load.

Re: Share Your Home Electrification/Efficiency Improvements

Posted: Sat Sep 07, 2019 11:33 am
by Oilpan4
I don't have to filter anyone or require any any kind of modification to the world around me.

I don't "just turn it off for a few hot hours" usually I turn it off in the morning when I get up at 4:30am and it stays off till I get home around 7. That's typical and I can leave it off for 2 up to 3 days in the summer, but that is not typical.
I wouldn't call 430 to 7 a few hours.

It depends on the type of air conditioner.
They are all not created equal.

My central is an older R410a system fixed speed compressor and mechanical thermal expansion valve when used in A/C mode. Pretty sure its not staged because of how old it is.
The manual says it gives up on trying to be a heat pump a +5F, starts using minimal electric heating at 38F.

Old central systems, some old splits and most window units run a fixed orifice and fixed speed compressor.
The fixed orifice and speed units need to be ran full blast for extended periods. If it were over loaded that wouldnt really be a bad thing.
Trying to do things that you think would save power really have little effect, such as slowing down the fan or cooling the condenser coils with cool water only reduce power consumption by around 10%.
Most of the power reduction you see when turning the fan speed down is just from the fan running slower.
The inside and out side fans may have 1 or 2 speeds.
These are your 10 to 12 seer machines. They're cheap above all else, efficiencywas an after thought.

The most common central air systems and most splits now use a single staged fixed speed compressor or 2 fixed speed compressors usually a big and small one, this has been around for ages on large commercial installs and use a metered expansion valve, usually a mechanical one.
These can be throttled down, be extra cooled on the condenser side during AC mode with say a ground based hest sink and it will reduce power consumption dramatically up to 75% for winter heatpumping, but usually only 1/3 to 1/4 for summer A/C.

Now we have variable speed compressors with thermal expansion valves on premium central units and splits. These give the best efficiency.
The compressor can slow way down to match the heat load saving the power of running the compressor at full speed when it's not needed. These can slow way down and go into high efficiency mode, not even needing the condenser fan to run, cooling off a big room with around 400 watts of power during the hottest part of the day.
They also don't try to start at full speed like a fixed speed, pulling a bunch of start up amps.
Good for if you want to go off grid.
The violent jerk to full speed is what helps wear out fixed speed compressors.

Re: Share Your Home Electrification/Efficiency Improvements

Posted: Sat Sep 07, 2019 3:40 pm
by Marktm
LeftieBiker wrote:
Fri Sep 06, 2019 2:37 pm

We've been doing this for 20 years: greatly reducing our grid consumption during peak loads (hot weather here) and doing more cooling in the morning and late at night. I remember poring through the regional ISO logs about 20 years ago, to get a feel for when local demand was highest and lowest, because they never made (or make) any effort to inform consumers about this issue.
Griddy got caught with proverbial "pants down" as many of their customers quit after one or two days and quickly signed up for the typical fixed rate contract. They have gone on quite an informational/educational campaign after that. If the majority of users where educated and gave a damn, the ERCOT grid would likely never have such an excursion. It has been hot, but not much more than expected. Rumors are that ERCOT does this periodically to drive "generators" to install more capacity. With $1.5 billion in three days, seems they can afford it!!

Re: Share Your Home Electrification/Efficiency Improvements

Posted: Tue Oct 22, 2019 8:16 am
by Oilpan4
Got my new 18k BTU inverter split installed.
It draws 10 amps at 240v when heating.
It does not appear to have backup heat and gives up heat pumping at +4F according to the manual.
Still going to use the wood stove as much as possible.
I will probably set the heat pump for 60F and if I want it warmer use combustion and run the heatpump to keep it from getting cold late at night after the fire goes out.

I have a 9k BTU premium efficiency split on its way for the bedroom. This one will try to heatpump down to -22F. Also 240v. I installed this exact unit in my rental house in 2016 and it has a backup heater grid. I'm curious to see if the latest version still has a backup heater.
The 9k BTU premium efficiency unit cost almost as much as a the 18k that went in the living room.

Re: Share Your Home Electrification/Efficiency Improvements

Posted: Thu Nov 14, 2019 11:47 pm
by Oilpan4
Had both the heat pump splits installed for almost 3 weeks now and I really like them.

Re: Share Your Home Electrification/Efficiency Improvements

Posted: Thu Nov 14, 2019 11:59 pm
by LeftieBiker
My mini split has proven to be better as a heater than as an A/C unit (except that it's more powerful as the latter). I get smaller swings in room temperature, although the remote thermostat still reads too high by 2 degrees (except for when it decides to be accurate and throw off my corrections). The built-in thermostat continues to read too high (it is near the ceiling) but still also wanders both ways, making it impossible to maintain a single room temp. So whichever thermostat I use I have to correct it at least twice a day. I also got a heat shortage this week, at about 18F: it was still providing heat, but only on the low fan speed - I couldn't raise it. I had to open my furnace duct for enough additional heat to keep my room warm. I deliberately (and with some misgivings) oversized the unit for my room, going with 18k instead of 12k, specifically so I would get the rated 9k of heat in the upper single digits. That seems to have been optimistic by at least 10F. My opinion remains that it wasn't really worth the huge amount of installation work...

Re: Share Your Home Electrification/Efficiency Improvements

Posted: Fri Nov 15, 2019 2:51 am
by Oilpan4
The one in the 9k btu split in the bedroom is supposed to be able to deliver 9,000 btu down to I think the manual said -10F.
I'm a little skeptical. It would appear my skepticism is well placed.
But I have a propane space heater just incase.
On that bedroom I can maintain 65F inside with a mere 5,000 btu heat input down to around 10F outside. So I shouldn't ever need the space heater unless the power goes out.

Re: Share Your Home Electrification/Efficiency Improvements

Posted: Sun Mar 01, 2020 7:17 am
by Oilpan4
Well the 9k btu inverter split in the bedroom did it, kept the room warm no problem down. To +5F out side.
The coal furnace has knocked off $100 per month off the winter electric bill every month for the last 3 years and the inverter splits at least another $50 for 2019.