Mini-split sizing

[DuckRyder]

Thank you, sorry to have been a bit absent.

I have sent a follow up to the two of the vendors requesting some clarifications. The one who quoted 24k/24k has already essentially said "overkill better than underkill".

The two I sent follow ups to it looks to me like one has gone to the low end of the manual J and one to the high end of the manual J.

RE the rest of the house: Its a 4 ton heat pump with an auxiliary natural gas furnace. I've been told by all that it wouldn't be prudent to shut the basement vents/return off. The basement is constantly cooler than the upstairs regardless of temp setting upstairs usually 5-10 degrees F.

as for the Solar heat gain coefficient no one asked for that and i don't know it, the windows are not here yet so they could not have looked. They were told they were LOW-E and double pane argon filled. So I'm guessing they used an average.

 

[DuckRyder]

Can anyone explain why an AC guy would say "mini-splits put out body temperature"?

 

[Gladtojoin88]

Because he's not correct and misinformed ... Ac is in the 30s and we have hyper heat Mitsubishi heat is much above body temp

 

[nickaluch]

My main concern is high humidity in the basement during the summer spring and fall. What's the plan on that ? If the AC is oversized it won't have a long run time to dehumidify. A cold clammy basement is no fun. Make sure the mini has a dehumidifier option if possible I'm not up on mini splits

 

[Wolf359]

Because he's not correct and misinformed ... Ac is in the 30s and we have hyper heat Mitsubishi heat is much above body temp

Or he's an AC guy and not an English major.

 

[Gladtojoin88]

Or he's an AC guy and not an English major.

I'm not sure I'm understanding what your saying

 

[Skippy722]

I'm not sure I'm understanding what your saying

Tradesman speaks in tradesman terms and forgets other people won’t understand it. I’m guilty of it… a “tenth” is 0.0001” to me, not 0.100” which is “a hundred thou.”

 

[PimTac]

Whatever you get , seriously consider a inverter equipped system. You will save on energy costs.

 

[Nick1994]

Can anyone explain why an AC guy would say "mini-splits put out body temperature"?

They run a lot, just very low. Very efficient to do so as they don’t have to cycle as much.

 

[brianl703]

Because he's not correct and misinformed ... Ac is in the 30s and we have hyper heat Mitsubishi heat is much above body temp

You know how they accomplish that feat? They slow down the indoor fan. Your standard split system won't do that, though I did find a thermostat with an outdoor temperature sensor and an output to run the air handler's fan at a lower speed at lower outdoor temps.

 

[Hillbilly Deluxe]

as for the Solar heat gain coefficient no one asked for that and i don't know it, the windows are not here yet so they could not have looked. They were told they were LOW-E and double pane argon filled. So I'm guessing they used an average.

Then nobody can properly calculate the heat gain. Low-E and Triple Double Sooper Duty Argon Neon Nitrogen filled quadruple pane windows have zero effect on solar heat gain. There is a SHGC number associated with each and every assembled piece of glazing (window/storefront/etc). This number is crucial in properly sizing the cooling load where you have expansive areas of glass with West, South and East exposure.

You can always call the tint guy later on to help fix it if it's really bad off.....

I'm just trying to help. My experience comes from designing HVAC systems for 25+ years and making mistakes.....like missing southwest exposure of some study rooms in a college dorm and not putting enough cooling in there. Seems college students get awfully uncomfortable trying to study or scroll social media at 82 degrees....


Also - there's some smart fellas in this thread, particularly in the later posts talking about inverter-driven compressors, low speed evaporator fans and how all that makes these mini-split systems MUCH better than the plain ole residential crap.

 

[PimTac]

Also - there's some smart fellas in this thread, particularly in the later posts talking about inverter-driven compressors, low speed evaporator fans and how all that makes these mini-split systems MUCH better than the plain ole residential crap.

Some of these systems are incredible. Where I lived in Asia I had a Panasonic inverter split installed. This was A/C only. The unit had all kinds of sensors. Sunlight sensor, people detection sensor, humidity and so on. The unit knew how many people were in the room and would adjust cooling based on that. If I left the room the unit would automatically spin down after a few minutes to save energy and spin back up when I came back. It would track me or anyone else in the room by directing the cool air towards me. I could sit in a chair and then get up to look out a window and the air followed me.

Lots of modes and functions as well. It also had uv and ozone capabilities and would tell you when cleaning was needed.

 

[PandaBear]

Tradesman speaks in tradesman terms and forgets other people won’t understand it. I’m guilty of it… a “tenth” is 0.0001” to me, not 0.100” which is “a hundred thou.”

Body temp is 36C or 96F, something like that. If you get that from a vent it is a furnace or heat pump in the winter, if you get that in the summer from an AC you will probably die.

 

[Hillbilly Deluxe]

I put a Daikin VRV-S Light Commercial multi-port system in my mother's house a year ago. Power bill was cut in half, comfort is off the chart. But this was $17,000. Don't choke. The cost for two typical residential split systems at 14 SEER and single speed compressors/evap fans was $12,500. It's pretty easy to amortize the $4500 difference when you are seeing a $1400 yearly reduction in power bills.

 

[PandaBear]

Some of these systems are incredible. Where I lived in Asia I had a Panasonic inverter split installed. This was A/C only. The unit had all kinds of sensors. Sunlight sensor, people detection sensor, humidity and so on. The unit knew how many people were in the room and would adjust cooling based on that. If I left the room the unit would automatically spin down after a few minutes to save energy and spin back up when I came back. It would track me or anyone else in the room by directing the cool air towards me. I could sit in a chair and then get up to look out a window and the air followed me.

Lots of modes and functions as well. It also had uv and ozone capabilities and would tell you when cleaning was needed.

The US style central residental HVAC is just lame for the cost they try to sell for. There, I said it.

You have one giant compressor, 1 giant blower inside the garage, 1 giant fan outside the house, a bunch of ductwork, a few small electronics here and there, then they sell you the system and install for 6-10k USD.

I get that they are heavy but in reality most homes would be better off using mini split or multiple small systems. If your system is 3 or 4 tons and have only 1 compressor and 1 blower, circulating the whole house, on or off only, or at most off, low, high, there's a lot of waste that totally could have prevented. Plus you have these massive seer difference between central and mini-split type system (even the most basic one speed mini split would be massively more efficient than a residential central AC).

I think the whole reason we have this mess of central HVAC / AC / furnace in the US is really a "cartel" running the show. It shouldn't be so wasteful and it shouldn't cost so much, but it makes a lot of people fat and lazy. I still respect the installers doing the work but I have no respect for the companies designing the products and the way architects design their houses like that. If I were to design I would have mini split or multiple small system for each side of a house, and if it is not big enough in extreme weather to turn them all on, maybe add one small central unit that will kick in to supplement it. It makes absolutely no sense the way we put in a worst case supersize unit in most houses when usually we only occupy one or two rooms at a time.

I think it is sad that smaller standardized system that user can install themselves (like they do in Asia) are not more popular here. If each room have standardized opening for mounting mini split and outside area to hang the lines / compressors then those 6-10k HVAC bill would immediately go down to 3-4k.

 

[PimTac]

The US style central residental HVAC is just lame for the cost they try to sell for. There, I said it.

You have one giant compressor, 1 giant blower inside the garage, 1 giant fan outside the house, a bunch of ductwork, a few small electronics here and there, then they sell you the system and install for 6-10k USD.

I get that they are heavy but in reality most homes would be better off using mini split or multiple small systems. If your system is 3 or 4 tons and have only 1 compressor and 1 blower, circulating the whole house, on or off only, or at most off, low, high, there's a lot of waste that totally could have prevented. Plus you have these massive seer difference between central and mini-split type system (even the most basic one speed mini split would be massively more efficient than a residential central AC).

I think the whole reason we have this mess of central HVAC / AC / furnace in the US is really a "cartel" running the show. It shouldn't be so wasteful and it shouldn't cost so much, but it makes a lot of people fat and lazy. I still respect the installers doing the work but I have no respect for the companies designing the products and the way architects design their houses like that. If I were to design I would have mini split or multiple small system for each side of a house, and if it is not big enough in extreme weather to turn them all on, maybe add one small central unit that will kick in to supplement it. It makes absolutely no sense the way we put in a worst case supersize unit in most houses when usually we only occupy one or two rooms at a time.

I think it is sad that smaller standardized system that user can install themselves (like they do in Asia) are not more popular here. If each room have standardized opening for mounting mini split and outside area to hang the lines / compressors then those 6-10k HVAC bill would immediately go down to 3-4k.

Good point. In my opinion energy costs are going to really skyrocket in the years to come. That will make systems like these become in demand over the whole house systems.

 

[PandaBear]

Good point. In my opinion energy costs are going to really skyrocket in the years to come. That will make systems like these become in demand over the whole house systems.

A lot of our "stuffs" were designed for the days when systems were expensive and energy / water were cheap. Look at those old apartment complexes, central water or even worse central heated water, for what? to save the cost of some copper pipes and some space to install a water heater?

 

[DuckRyder]

...

I'm just trying to help.

...

I know and I appreciate it and everyones help, if I said anything that implied otherwise I did not mean it that way.

I dug out the window quote and it does have this on it:

Performance Information: U-Factor 0.29, SHGC 0.30, VLT 0.56, CPD PEL-N-136-00054-00003, Performance Class R, PG 30, Calculated Positive DP Rating 30, Calculated Negative DP Rating 30, Year Rated 08|11, Clear Opening Width 26.488, Clear Opening Height 56.5, Clear Opening Area 10.39286, Egress Meets Typical 5.7 sqft (E) (United States Only)
Grille: No Grille,

The door quote does not seem to have any similar info, only the "man door" is exposed, it is a Therma Tru S2000 full light.

I thought all of the systems I was looking at were inverter driven, but I will double check.

So far ive been quoted a

Mitsubishi MXZ-3C30NA2

Daiken RXB36AXVJU

And a Gree Multi42 (trying to nail the model number down)

So far pricing is between about 7000 and 13000. (ouch)

 

[brianl703]

I get that they are heavy but in reality most homes would be better off using mini split or multiple small systems.

Around here a lot of builders have been using two central AC systems, one for downstairs, one for upstairs.

There's just one small problem with that....the upstairs unit usually goes into the attic, along with it's ducts. (The downstairs unit goes into the basement)

Putting HVAC equipment into a hot (or cold) attic is really an energy waste (and not good for the equipment either).

I lived in a house where just the ducts for upstairs were in the attic. The furnace/air handler was in the basement.

In the winter when the heat came on? It blew freezing cold air for at least 30 seconds.

In the summer when the AC came on? It blew burning hot air for at least 30 seconds.

What I have in my house now is:

One 4-ton unit (AC/heatpump) with air handler in the basement, with all duct work between floors (nothing in the attic), with an Aprilaire zone controller and two thermostats, one for upstairs, one for downstairs.

You can look to the left to see where I live, and know that my highest electric bill EVER (I do not use propane for heating, only cooking) has been around $200 and that includes an electric water heater, well pump, pumps for a septic system, and charging a Chevy Volt which usually gets driven around 20 miles a day.

I even have a switch on the aux heat for the heatpump so it won't come on unless the heat pump is running a defrost cycle. The Honeywell thermostats I have are way too quick to turn on aux heat when it really isn't needed. I never turn that switch on.

It's wired between the W1 wire on the zone controller and the air handler:

 

[PandaBear]

Around here a lot of builders have been using two central AC systems, one for downstairs, one for upstairs.

There's just one small problem with that....the upstairs unit usually goes into the attic, along with it's ducts. (The downstairs unit goes into the basement)

Putting HVAC equipment into a hot (or cold) attic is really an energy waste (and not good for the equipment either).

I lived in a house where just the ducts for upstairs were in the attic. The furnace/air handler was in the basement.

In the winter when the heat came on? It blew freezing cold air for at least 30 seconds.

In the summer when the AC came on? It blew burning hot air for at least 30 seconds.

What I have in my house now is:

One 4-ton unit (AC/heatpump) with air handler in the basement, with all duct work between floors (nothing in the attic), with an Aprilaire zone controller and two thermostats, one for upstairs, one for downstairs.

You can look to the left to see where I live, and know that my highest electric bill EVER (I do not use propane for heating, only cooking) has been around $200 and that includes an electric water heater, well pump, pumps for a septic system, and charging a Chevy Volt which usually gets driven around 20 miles a day.

I even have a switch on the aux heat for the heatpump so it won't come on unless the heat pump is running a defrost cycle. The Honeywell thermostats I have are way too quick to turn on aux heat when it really isn't needed. I never turn that switch on.

It's wired between the W1 wire on the zone controller and the air handler:

View attachment 90147

When I said most homes are better off with multiple system I didn't mean 1 in attic 1 in basement or garage, that's no good either.

What I meant was a "little place outside the wall where you put the compressor unit of the AC away from bedroom, and a line that goes to the indoor unit of each room for the mini split. If done right it shouldn't be loud, and it should be individual room control.

Still if you want to use natural gas to heat in the winter this may not work, but for area that are better served with heat pump, multiple ductless individual units are better.