danrjones
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Location: Ridgecrest, CA

HVAC Discussion

Wed Apr 14, 2021 1:34 pm

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.
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dmacarthur
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Re: HVAC Discussion

Wed Apr 14, 2021 1:55 pm

How many square feet are you heating and cooling? your numbers look about right for a 2000 square foot house......
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danrjones
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Re: HVAC Discussion

Wed Apr 14, 2021 2:07 pm

dmacarthur wrote:
Wed Apr 14, 2021 1:55 pm
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.
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danrjones
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Joined: Wed Apr 17, 2019 8:02 am
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Location: Ridgecrest, CA

Re: HVAC Discussion

Mon Apr 19, 2021 7:20 am

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.
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danrjones
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Re: HVAC Discussion

Mon Apr 19, 2021 7:43 am

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.
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ripple4
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Location: Toledo, Ohio

Re: HVAC Discussion

Thu Sep 09, 2021 5:25 pm

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.

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LeftieBiker
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Re: HVAC Discussion

Thu Sep 09, 2021 6:12 pm

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...
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goldbrick
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Re: HVAC Discussion

Fri Sep 10, 2021 12:17 pm

ripple4 wrote:
Thu Sep 09, 2021 5:25 pm
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?

ripple4
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Re: HVAC Discussion

Fri Sep 10, 2021 3:31 pm

LeftieBiker wrote:
Thu Sep 09, 2021 6:12 pm
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.

danrjones
Posts: 1155
Joined: Wed Apr 17, 2019 8:02 am
Delivery Date: 17 Jun 2019
Location: Ridgecrest, CA

Re: HVAC Discussion

Wed Sep 15, 2021 1:02 pm

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.
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