New Home HVAC System

[riptides]

...

That's a stunningly beautiful pic.

 

[jk96]

That's a stunningly beautiful pic.

Thank you.

 

[Popgadget]

One of the reason that mini splits are typically so efficient is the technology that they use. Both indoor and outdoor fans are variable speed as is the compressor. The expansion device is a needle valve operated by a stepper motor. The entire process is monitored by a micro processor that continually adjusts all parameters according to the load. This can provide efficiency that exceeds a closed loop geothermal system depending on the actual equipment used.

Having said that, the downside is that unlike a conventional heat pump with an orfice or basic TX valve, they are much more difficult for a “generic” technician to diagnose and repair.

In the real world this means the percentage of a repair being made on the first trip is slim compared to a conventional system.
And then there is the question of parts for units that are 10 years old.

There is always a cost for being on the cutting edge.

 

[Sigarms]

I would guess at least 75% of HVAC contractors for retrofit applications do not do a full manual J load (at best, perhaps a block load)./QUOTE]

Ours actually did a manual J. Came out to 7 tons. Upgraded to 8 he said for airflow. After the fact he did admit he had not done many homes with spray foam. Also the cathedral ceiling (26 ft) and all the windows throughout the home threw him off as well. He seemed shocked we were only running stage 1 and no backup heat in zero temps the first winter. In reality we probably needed 5 tons without heat strips or 3.5 to 4 tons with heat strips on sub zero temps.

Apparently he didn't do his manual J correctly when he put in an 8 ton system and it appears a 5 ton would of worked. Oversizing by 3 tons shouldn't be your issue. Hopefully he made it right.

Nice room! Whenever I'm dealing with something new that I'm not certain of, I'd be making phone calls to ensure my butt is covered.

Have a homeowner right now filing a complaint on another contractor. 2 ton system went into a 650 sqaure foot house because the homeowner wanted it cooler in the summer time so the guy thought more AC was the answer.

You have a 4,500 sq ft house where it appears that 5 ton will suffice. We bought our house used, built in 1988. 3,500 square feet, lots of windows on the first floor, we need every bit of 7 tons between 3 systems. Before we bought the house I went over the ductwork. It was perfect.

This is why load calculations are so important. Garbarge in, garbage out per the data as most guys just go by 600 sq ft per ton and add or deduct 1/2 ton between "good" and "bad" on the insulation and if they don't come up close to the "general rule" they freak out and try to change the data to what makes sense to them

 

[jk96]

Apparently he didn't do his manual J correctly when he put in an 8 ton system and it appears a 5 ton would of worked. Oversizing by 3 tons shouldn't be your issue. Hopefully he made it right.

Not really but in the long run it worked out. Really big credits from the electric coop per ton for geo offset most of the extra tonnage expense. Biggest headache was figuring out how to make it work to prevent short cycling and high indoor humidity while he drug his feet about downsizing the units. I figured out how to trick the units zone percentages so it never called for 2nd stage. That and some slight zone bleeds took care of the short cycles. In the end I have a pretty efficient system. Running stage one only my loop is oversized a bit now so loop temps don't draw down much in the winter or up in the summer giving more delta t. Additionally in the winter we don't have a need for backup electric heat. I will give him credit on the duct work. Some of the nicest hvac duct I've seen done in residential.

 

[kf4uda]

I would like to thank everybody for posting their experiences and opinions. Definitely some great feedback here. I will use all of your feedback when it comes time to meet with the HVAC contractor to ask questions.

 

[kenmac]

No matter what brand ,or type system you choose. Be sure it's a clean install. In other words clean copper line sets, flow nitrogen during brazing, and proper vacuum, etc, will determine how long your investment last

 

[ustmd]

There is a builder I follow on Youtube--Matt Risinger.

He builds high end custom homes here in the Central Texas. He is very focused on modern building science and energy efficiency. He is doing a series on the remodel of his personal home and he is using a mini split type system for the home:

Mitsubishi HVAC At My House - Full System Tour - YouTube

The video is a little long, but he walks through his thinking along with providing the load and energy analysis.

 

[RoyKing]

A tight well insulated house with with geothermal with all the ductwork in condition areas is easy to keep running if a large house use two units, keep duct pressure low with adjustable registers and balance the house. A electronic air cleaner on return removes all odors and a heat exchange for fresh air and keep the house under positive pressure. In some areas a humidifier might be needed. If you like hot steamy showers vent it outside

 

[Popgadget]

A tight well insulated house with with geothermal with all the ductwork in condition areas is easy to keep running if a large house use two units, keep duct pressure low with adjustable registers and balance the house. A electronic air cleaner on return removes all odors and a heat exchange for fresh air and keep the house under positive pressure. In some areas a humidifier might be needed. If you like hot steamy showers vent it outside

When I built my house 35 years ago, it was pretty much as you described. Urethane foam from under basement slab to the 2nd floor ceiling joists. All ductwork in conditioned spaces and open loop geothermal with electronic air filter. I’m on the third heat pump since then, each one has been an improvement over the previous one. The current one is a ClimateMaster with variable speed blower, multi stage compressor (but not variable) and modulating water valve. The electronic filter has been replaced with MERV 16 media filter and UV light.

But if I were to do it today, I would take a hard look at mini-splits. They are where the cutting edge of efficiency is now, and offer multi zones without the penalties of trying to zone ductwork. There are certainly disadvantages to them, but in many cases they are the way to go.