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danrjones

Well-known member
Joined
Apr 17, 2019
Messages
1,443
Location
Ridgecrest, CA
Created this new thread for HVAC discussion. Will leave it here under solar.

Here again is a link to the Load Calculator I've been using:

https://www.loadcalc.net/load.php

I'm still tinkering with my numbers. Windows seem to be the biggest problem in my house. They were single pane but I've replaced two already with double and have two more on order.

The next biggest issue depends on heating or cooling season. For heating, my floors are the next biggest problem and I can't really do much. A slab is a slab. For Cooling season, the second biggest issue is either duct load or ceiling. I have to go up in my attic and decide what R value my ducts actually are. Currently I'm running with the setting at R-19 for attic, R-13 for walls and R-4 for ducts. These could all be wrong. Knowing your inputs are vital to get good numbers out of the calculator. I've measured everything else, windows, doors, etc. I've tried measuring the attic insulation but its a mix of blown and bat, and the blown in fiberglass is uneven. It is a late 80's house in the desert in CA so R-19, while it sounds low, might be correct.

For Design temp inputs for cooling I have put in indoor of 75f without Outdoor 110f, and for Heating outdoor 20f and indoor 68f.

Currently with these inputs I'm getting a Load of:
Total Btu's Cooling: 43347
Sensible Load: 42747
Latent Load: 600
Total Btu's Heating: 50479

More to come on my past usage for my NG furnace and systems I'm looking at, their design BTUs and DIY issues, and fitting it in with my Solar.
 
How many square feet are you heating and cooling? your numbers look about right for a 2000 square foot house......
 
dmacarthur said:
How many square feet are you heating and cooling? your numbers look about right for a 2000 square foot house......

1810 sqr feet, but I have high ceilings in several rooms. I have my cubic feet set at 21720, which is another number I need to spend more time on.
 
Over the weekend I ripped out my old NG furnace. A bit of a pain because it was heavy, but my son and I finally lifted it out and carried it outside. An old Heil furnace, maybe 80% efficient, from the late 80's or very early 90s. The heat exchangers though looked to be in good shape.

So now I have until November to figure out what I am doing to replace it.

I'm still leaning toward a heat pump, I think its a good fit in our area.
Pouring through the spec sheets for some models' I've noticed just how different one unit to the next can be.

For example, if you look at a Mr. cool Universal 5 ton you see:

Outdoor Temp / Capacity (BTUs) / Input Watts / HSPF / COP

17f 49000 7100 6.90 2.02
32f 54000 6600 8.18 2.40

Then compare to a Goodman 5 ton:

17f 34600 4100 8.4 2.3
32f 41580 4600 9.0 2.65


As far as I can tell, HSPF is just the BTU output divided by the kW input. You can also look at COP, Coefficient of Performance, which looks at btu output / btu input (or kW output / kW input)

Anyway, either way, the Goodman appears to be more efficient at the lower temp BUT the Goodman has a significant reduction in output.
The Goodman unit falls well below my needed BTUs at the lower end of the temperature I'm looking at, which would mean installing the emergency heat strips, which have a COP of 1. So that higher looking efficiency of the Goodman would quickly dissapear when heat strips turn on.

As a side note, a "5 ton" unit theoretically should move ~60,000 btus or 12k btus per ton.

I think the takeaway for me is that yes, some heat pumps are much better than they used to be at cold temperatures. But they appear (per their spec sheets) to not be created equally. In fact, the 4 ton Mr cool Universal is almost as good at the 5 ton at those cold temperatures. Well, cold for where I am... YMMV.

Here is the 4 ton system:

17f 48000 6880 6.98 2.05
32f 48000 5800 8.28 2.42

So, if I'm reading the spec sheets correctly, it tells me one really needs to dive into literature beyond just the 1 page glossy product flier.

I have to go look to see how the commercially installed (non DIY) systems like Carrier and Lennox and Trane compare.

*IF* I went forward with the Mr. cool 4/5 ton unit, I'd likely install a 5 kW (small) heat strip, mainly for defrost cycles. But not the standard 15 to 20 kW strips, as I just don't need that much heat. I'm going to post more on my prior NG consumption with some estimates later based on my old furnace.
 
I guess for those two systems I also should have posted cooling, though I have a whole house swamp cooler, so AC would matter less to me.

Mr. cool Universal:

Outdoor Temp / Capacity (BTUs) / Input Watts / EER

105f 54000 6650 8.12
115f 46000 5700 8.07

Then compare to a Goodman 5 ton:

105f 50800 5100 9.96
115f 47900 5750 8.30

But these may not be perfect comparisons, as the Goodman Spec sheet requires you to choose indoor wet bulb temp, while the Mr. cool does not list indoor wet bulb as part of its spreadsheet.
 
I wanted to share my recent installation on a 12,000BTU mini-split in my two story, 2200sqft house. It was always part of my plan to install this with my off-grid solar, but it took 2 years to get it done. The trick is that I installed it in the stairwell between the first and second floor, one bonus feature is it has a programable louver to point down or strait out. So in the daylight hours it points down and keeps the first floor >>15F lower than the outside temp. Then in the evening its programed on a schedule to blow strait out into the bedroom hallway. Its very effective and cooling the bedrooms. To compare my 3-ton 10-seer ducted unit to this new 1-ton 20seer unit, consider my average usage from 2013 to 2017 before I had solar. I would typically have 400kwh more than my spring and fall bill from June to September, due to the A/C running. With the mini-split I have a power meter installed and it used 190kwh this August, which had a long 90+F streak in it (Ohio).

The 10,000 foot view is that in 2013-2017 I used 1350KWH in the summer, paid $250/month in diesel for my old car (Jeep liberty CRD), and had the AC set to 78F. The deal 8/2021 and onward is that my monthly power utility bill is 300kwh and the AC is set to 74F, and the Nissan Leaf is charged everyday, Its a home energy ecosystem.

The total installed cost for the mini-split was $1300. $660 for the AC unit (DAIZUKI - DXTH12X426-20), $150 for the 25' lines, $260 for the pro leak check/vacuum and then the balance is finishes. There is a $300 federal rebate on heat pumps in 2021. With the heat pump and AC acting, I figure I can save $270/year, or a 4 year payback.

 
I still have trouble with my 18,000 btu mini split, but it hasn't stopped working, and it will run from the generator. Now, if I could only get it to obey its own thermostat in "Dry" mode - or in any other mode for that matter...
 
ripple4 said:
I wanted to share my recent installation on a 12,000BTU mini-split in my two story, 2200sqft house.

Thanks for the info. Is that the only output for the system in the entire house? Is it your only heat source as well or do you have others?
 
LeftieBiker said:
I still have trouble with my 18,000 btu mini split, but it hasn't stopped working, and it will run from the generator. Now, if I could only get it to obey its own thermostat in "Dry" mode - or in any other mode for that matter...

This brings up a great point. All the fancy HVAC equipment in the world cannot help if the controls are ugly. There is an XKCD out there showing the digital resource lifespan. (https://xkcd.com/1909/) In a not joking way these Asian-made, WIFI connected devices won't be supported for ever and not as long as the hard parts will last . I ran a low voltage control wire with the lines and power wires so that I can, if needed, have a IR blaster remote control it.

The house already has a 100KBTU 80% AUFE NG furnace, and a 3-ton 10 SEER central AC unit that works perfectly well. This central AC unit takes too much surge current to start so this mini-split is a way to get air-conditioning off-grid. I paired it with a 1kw vertical solar panel array, and in the fall and late spring I could replace some natural gas, but in the dead of winter, its fossil power for now.
 
An update on my project, I ended up ordering the Mr. Cool Universal 5 ton system from Home Depot.

I'm slowly getting things ready for the install - I had to run a new 240 volt line to my HVAC closet, as the old air handler only ran off a 15 amp 120v circuit. I finished that this last weekend. Next I have to install the Air filter (An AprilAire filter, on its way to me), then I can install the air handler in a vertical stack on top of the filter, then the outside condenser unit, and finally the line sets.

I did order a heat strip kit. I probably don't really need it, even my old NG furnace was only 80% and 48k btu, so the new 5 ton unit should be more than enough heat to cover my warm location. But the heat strip does offer some advantages - first, if the condenser breaks, I can still heat. Second, during the occasional defrost cycle, it can kick on for a few minutes. And third, I got to buy a bigger wire! Wire is awesome.

I'll update when I finish. Luckily I have time, it doesn't get cold here until mid to late November.
 
This brings up a great point. All the fancy HVAC equipment in the world cannot help if the controls are ugly. There is an XKCD out there showing the digital resource lifespan. (https://xkcd.com/1909/) In a not joking way these Asian-made, WIFI connected devices won't be supported for ever and not as long as the hard parts will last . I ran a low voltage control wire with the lines and power wires so that I can, if needed, have a IR blaster remote control it.

Just to be clear: I don't have the WiFi set up, or the card for it installed. I'm just using the IR remote that came with the system. I'm not sure that it's the remote that is the issue, as the remote will read a more or less correct temp, but the mini split will either ignore it or stay within about 2 degrees high or low of that temp. The temp probe for the system is covered with a plastic tube, presumably to both protect it and to buffer the speed of temp changes being read. I've often considered removing that plastic tube, but then the probe would get covered with the dust that this house produces in vast amounts.
 
LeftieBiker said:
Just to be clear: I don't have the WiFi set up, or the card for it installed. I'm just using the IR remote that came with the system. I'm not sure that it's the remote that is the issue, as the remote will read a more or less correct temp...

I have seen that there are two groups of IR remotes, one way and two way. bassically the remote is smart or not. for a window AC unit I previously had installed a Broadlink WIFI IR remote that is smart and phone controlled. maybe that will control better?

https://www.amazon.com/gp/product/B085WYQ1XM

danrjones said:
An update on my project, I ended up ordering the Mr. Cool Universal 5 ton system from Home Depot.
...
I'll update when I finish. Luckily I have time, it doesn't get cold here until mid to late November.

Please do update when finished. I would like to know if the large ducted heat pump is more economical than the mini-split approach. something like how many kWh the system uses and how many cooling/heating-degree-days that was spent over. For example the only data I have so far is from my august power bill which was the highest temperature average on my bill ever, 79F. The minisplit used 208kWh and the furnace circulator fan (60w, 625rpm) that runs 6.25 hours per day to blow the cooling around used 12kWh for a total of ~220kWh for 124 cooling degree days. (4 degrees between 79F average temp and 75F thermostat, times 31 days.)
 
I just want to give a shout out for this guy: https://www.energyvanguard.com/blog/
I've been reading his stuff for a while and he seems really on top of the science and is a good writer. There are lots of links to other sites and more in-depth reading also.
 
I have an update on my HVAC project. After slowly working on it over the last month or two, I finally ran the line sets over the weekend and fired it up last night to test. I still have aesthetic / finishing work to do, such as a line set cover, repairing the HVAC closet where the air handler went in (I had to enlarge it compared to the old furnace, so now it needs a new larger door), etc

But my son and I tested it last night - ran it in AC mode, then ran the emergency heat strip, and then ran the heat pump. All seemed to work as intended. Nice to see a lot of hard work pay off, lest the wife tell me I should have hired a professional. It isn't really cold or warm enough right now to need Ac or Heat, but soon we should be using the heat pump in the mornings. The heat pump certainly put out a lot of heat - I remember the old days where heat pumps produced luke warm air. Within just a few minutes it was putting out high volume of 110f air and still climbing. Nice and warm, no complaints at all. And the outside unit is super quiet - not like the old school units.

I know i described the unit earlier, but here is a link to it at Home Depot at the bottom.

I went with the 4/5 ton unit, currently set for 5 ton operation. I used the 50 ft precharged lineset - I wish I could have done 35, but when I measured the distance I came up with 34' and I don't like cutting things that close. I was able to route it all through my attic in an arc shape using all 50 ft anyway, so it worked well.

https://www.homedepot.com/p/MRCOOL-...tall-Kit-208-230-Volt-UNIB18060NK50/314983820
 
I'll post more detailed test results on how the unit actually does later, but I did take a quick look at energy consumption last night when testing. It was about 70 f outside, which isn't really ideal for testing heat or AC.

When running in AC mode, the unit was pulling about 3 kW. I know from the spec it will pull a lot more than that when it needs to run the outside compressor at a higher level. When running in heat pump mode, it was pulling about 5 kW. This also is not at max per the spec. And when I tested the heat strip, it was pulling 10 kW - which makes perfect sense, as I installed only a 10kW heat strip. The 5 ton unit recommended the 15kW or 20 kW heat strip, but I thought that was way too much for my area, plus it would have required TWO 60 amp breakers and double the wiring. Don't need that where I live.
 
The Mr. cool DIY 2/3-ton ducted split that we are talking about looks like the go-to model for furnace replacement. considering that a traditional 95% AFUE + 13 seer aircon is going to run $9k+ from a HVAC place, the Mr. Cool DIY is starting from a great cost position. I found someone who did the natural gas with an old furnace to mr. cool full year review. he just about broke even with large savings in the summer with the high seer aircon, then a little more cost in the winter in heat pump mode, so he says its about a wash. the thing to keep in mind is that the natural gas service has a fixed cost, I've heard people say their summer bill it $15, but mine is $45. so adding in the savings from not paying that $500/year tips it to heat pump. the goal is to be all eletric.

(https://www.youtube.com/watch?v=7MB64_jVLZk)

On my ductless minisplit experiment I calculated the numbers for each month of the heating season to see how many kWh/day I would need to have used in order keep costs under the spending level of my historical costs on NG. so in October I would normally burn 0.7 Ccf per day more than the summer, so its the gas directed solely to space heating and (at my specific, contracted gas and power rates) that's the same cost as 2.8 kWh, so if I'm less than that on average I'm on track. So far, I'm right at that power usage rate, so its costing me the same as NG at this point. Of course, I don't pay the full retail rate because more than half my generation is from solar even in October, so its a much better deal than that. however, I'm trying to show even without a huge solar array, or in a cloudy streak, they might break even with a heat pump.


these are the calculated numbers based on 5 years of historical NG usage, I'll collect the data and see how it looks by June '22. My goal is that I don't go over $130 for my raw power and gas bill combined all winter.

2200sqft home in toledo ohio:
October/ .7 Ccf -2.7kWh/day /avg temp-65F
November/1.6 Ccf - 3.8kWh/avg temp-53.9F
December/2.5 Ccf - 11 kWh/avg temp-46.6F
January/3.6 Ccf - 13.7 kWh /avg temp-36.5F
February/4.8 Ccf - 15.6 kWh/avg temp-29F
March/4.4 Ccf - 11.1 kWh/avg temp-31.7F
April/2.7 Ccf / 8.7kWh/day / avg temp-42.9F
May/2.1 Ccf/4.8 kWh/day avg temp-48F
 
danrjones said:
Created this new thread for HVAC discussion. Will leave it here under solar.

Here again is a link to the Load Calculator I've been using:

https://www.loadcalc.net/load.php

I'm still tinkering with my numbers. Windows seem to be the biggest problem in my house. They were single pane but I've replaced two already with double and have two more on order.

The next biggest issue depends on heating or cooling season. For heating, my floors are the next biggest problem and I can't really do much. A slab is a slab. For Cooling season, the second biggest issue is either duct load or ceiling. I have to go up in my attic and decide what R value my ducts actually are. Currently I'm running with the setting at R-19 for attic, R-13 for walls and R-4 for ducts. These could all be wrong. Knowing your inputs are vital to get good numbers out of the calculator. I've measured everything else, windows, doors, etc. I've tried measuring the attic insulation but its a mix of blown and bat, and the blown in fiberglass is uneven. It is a late 80's house in the desert in CA so R-19, while it sounds low, might be correct.

For Design temp inputs for cooling I have put in indoor of 75f without Outdoor 110f, and for Heating outdoor 20f and indoor 68f.

Currently with these inputs I'm getting a Load of:
Total Btu's Cooling: 43347
Sensible Load: 42747
Latent Load: 600
Total Btu's Heating: 50479

More to come on my past usage for my NG furnace and systems I'm looking at, their design BTUs and DIY issues, and fitting it in with my Solar.

Good work and approach. This is one of the things I appreciate about air space heat pumps: no A/C to the slab or the attic. Only to the room air where people are. Although admittedly a WAG, I calculate that 30% of my furnace heat is lost via the ducts to the air spaces above our living volume. When I look at my ceiling, I see it as a barrier I have to improve.

HOWEVER, don't pay too much attention to insulation until you have taken care of unwanted ventilation (leaks). A tight home with good air quality is a difficult task for retrofits, but it really is the key to success.
 
Sounds like justification for buying myself a moderately priced thermal camera. I can tell my wife it is to find the air gaps and leaks. Which would be true!

Funny thing, I have this nice new heat pump waiting to be used... and it was in the 80's yesterday. I turned our swamp cooler back on yesterday afternoon. More upper 70's and 80s this week too. In November. That's unusually warm even for us.

Now my project is at the parts I don't enjoy as much. Building a door for the HVAC closet, repairing drywall, trim, etc
 
danrjones said:
Sounds like justification for buying myself a moderately priced thermal camera. I can tell my wife it is to find the air gaps and leaks. Which would be true!

If you have a smartphone, the Seek Thermal will do the job. Great for spotting areas that need sealing or insulation, also for detecting problems with electronics or electrical equipment.
 
Nubo said:
danrjones said:
Sounds like justification for buying myself a moderately priced thermal camera. I can tell my wife it is to find the air gaps and leaks. Which would be true!

If you have a smartphone, the Seek Thermal will do the job. Great for spotting areas that need sealing or insulation, also for detecting problems with electronics or electrical equipment.

thanks! I'll check that out.
 
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