Installing Ducted Mini-Splits and ERV in Modern High Performance Home

Things are really moving along on the Proud Green Home at Serenbe. This past Friday, the mechanical inspector paid a visit and we passed! Ahead this week; the builder has ordered the final plumbing inspection, the sprayfoam contractor is installing the open-cell foam in all the walls and roof, we will be performing the pre-drywall inspection for EarthCraft House and ENERGY STAR certifications, and we will be hosting a construction tour of the home with the builder. If you're in the Atlanta area this Wednesday, please stop by! We'd love to show you around.

For those of you who can't make it, here are photos from the installation of the heating, ventilation and air conditioning systems that just passed the rough-in inspection last week. VIS VIVA Energy and Services, a local contractor who have successfully installed many of our HVAC designs, installed all of the systems. Vis Viva is also providing the additional air sealing services and installing the spray foam for the home.

As mentioned in a previous post, the home wlll be heated and cooled by the Ducted Mini-Split Heat Pump system (a.k.a. Variable Refrigerant Flow, VRF) by LG Electronics, and fresh air will be provided throughout the home by Zehnder America. Feel free to check out Zehnder America's video on how their systems work, narrated by a guy with a great German accent!

Design Summary:

  • Design per ACCA Manual J, S, T and D, and ASHRAE 62.2
  • Home: 2,700 Square Feet, 4 Bedrooms, 3.5 Baths
  • Design Temperatures: Heating - 26°F, Cooling - 91.5°F
  • Heating Load (99%): 22,700 Btuh
  • Cooling Load (1%): 18,960 Btuh (Sensible), 2,400 Btuh (Latent)

Heating and Cooling Equipment Summary:

Ventilation Equipment Summary:

The Installation

The HVAC Contractor, VIS VIVA Energy and Services, showing up for duty, SIR!

Hauling in the concealed ducted fan coils, and Lance Beaton (Owner, VIS VIVA) in the background "making a plan" with his crew chief, Julio.

One of VIS VIVA's crew bringing in a couple of the custom supply and return plenum transition pieces.

Our specifications call for a maximum tested duct leakage of 2% (or 2 cfm per 100 s.f. of conditioned floor area). A liberal use of mastic is a really good way of achieving that. Here is one of many connections showing the mastic at least "a nickel thick". VIS VIVA has consistently been delivering 2%, or less, duct leaking on recent jobs. Well done!

Here is a shot inside one of the supply register boots. Now THAT is what I call a "liberal" amount mastic!!

Julio and the fellas insulating one of the main supply take-offs, and doing a neat and tidy job of it. Very snug!

Here is one of the three concealed ducted fan coils being used to serve three separate zones in the home. This one, a 9,000 Btuh capacity unit, will serve the entire second floor where we have 3 bedrooms, 2 bathrooms and a flex space.

Here is the 12,000 Btuh fan coil serving the main living area, kitchen, dining and foyer. It's being installed in a dropped ceiling area in a small alcove just outside the Laundry Room. Vertical clearance for these units is 12". Transitions allow the plenums to deliver or return adequate air flow to and from the unit.

The upstairs unit in the encapsulated attic with the refrigerant lines ready to be attached. All ductwork was insulated to a minimum R-6.

The third ducted unit in the Master Suite. It will be installed like the one serving the main living area between the floor joists and dropped ceiling framing in the His Closet of the Master Bedroom.

Ductwork installed withing the floor structure using ACCA Manual D Duct Design methods. The 2'-0" extension helps build up static pressure in the duct system for better air flow and delivery.

When we designed the house, it structural system, and the HVAC system, we lowered beams where we needed to allow the routing of ductwork. We used this as an opportunity to break up the open interior spaces (visually) of the main living, kitchen and dining areas. Normally the beam would be flush with the top of the floor joists, but planning ahead allowed all of it to work together. Win, win, win!

The main exchanger (or dampener) of the ComfoAir 350 ventilation system getting ready for set up and install. That's Lance Beaton (Owner, VIS VIVA) laughing at me for trying to pick it up and put it in the attic without any off!!

In this exchanger, the "magic" happens. Fresh air comes in, it flows by air being exhaused from the house, and the fresh air stream recovers up to 90% of the heat energy from the outgoing air to pre-condition it before it enters the home. The four ports are for 1. Fresh Air intake, 2. Stale Air Intake, 3. Fresh Air Supply, and 4. Stale Air Exhaust. See the link for the video above for more on how the system works.

Main distribution boxes ready for assembly. One for fresh air and the other for stale air.

Installed on an exterior wall in the attic, the exchanger and distribution boxes are placed to allow for short runs of the main supply and exhaust ductwork. The exhaust and fresh air intake on the exterior wall will be placed a minimum of 10'-0" apart.

The distribution ductwork is a flexible piping with a smooth inside and ridged outside. Each of these ducts will deliver supply air or return stale air to and from the distribution boxes.

Supply and/or return boxes that are installed in each room. Once the drywall is installed the cylinders are trimmed flush and the "designer" diffuser is installed.

Here is another type of return box. This one has been installed in the powder bath on the side wall instead of the ceiling. A different "designer" diffuser will be installed after drywall.

That's a wrap, folks!

Until next time, thanks for tuning in and watching one of our "babies" grow up!

Please let us know what you think of the progress or the systems we chose. If you can make it to our event, we look forward to meeting you. Please come say, "hello"!

Written by Chris Laumer-Giddens





Views: 31098

Tags: Architecture, Atlanta, Design, Ducted, ERV, Efficiency, Green, HVAC, Heat, High, More…Home, Installation, Mini-Splits, Modern, Multi-V, Proud, Pump, VRF, and


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Comment by Franco Oyuela on August 7, 2018 at 1:33pm

With ducted mini-split systems, evaporators are generally located close to the distribution point, which leads to a reduced amount of air leakage and dirt build-up in ductwork related to mini-split systems. Ducted mini-split systems allow users to take advantage of high-efficiency inverter technology.

Comment by tedkidd on April 13, 2013 at 10:18am
"Getting rid of lossy/restrictive ductwork is a quick way to get a 30% boost in real world efficiency, yet the specs of the minisplits don't reflect this real world savings."

Think maybe tracking use, and making these unseen Real World savings SEEable, might better solve the adoption issue?

I disagree that it's a price problem. I think it's a belief problem, people are so often disappointed by efficiency promises they don't believe them, or other performance benefits "claimed". So they don't factor them.

Lower price won't flip some magic switch, that analysis is incorrect. Price is irrelevant when benefit can't be seen. Anyway, complaining about price is like complaining that it's raining. There is no solution down that road,

People like to see results. They provide confidence. People have no problem paying more when they know they will get more. Confidence in results is the problem, transparency of past results is the solution.
Comment by Bob Blanchette on April 13, 2013 at 9:12am

Inverter based technology is marketed as a premium product with high margins, IMHO that's a big reason we don't see it much in this country. If it were common as in other countries price would drop dramatically. Minisplits as primary heat/cooling systems are also rare. Getting rid of lossy/restrictive ductwork is a quick way to get a 30% boost in real world efficiency, yet the specs of the minisplits don't reflect this real world savings.

Inverter drive technology will replace the current systems, but not until either the price of equipment drops or the price of power goes up. We have some of the lowest power rates in the world, hence the slow move to higher end HVAC systems. 75% of all electric homes in our area use 10-20KW of STRIP HEAT as a primary heat source, this would never happen anywhere other than the US on such a large scale. Power is only 6 cents per KWH during winter months, a price rarely seen in other parts of the country.

Oversizing is an issue for sure, getting contractors to stop grossly oversizing on 99% of installations is the bigger battle than getting it perfect on a handful of installs. A custom designed/installed HVAC system is something that happens about 1% of the time in residential. Most contractors STILL use 500sqft per ton for cooling and if a load calculation is required by code the contractor just fudges the inputs so the result comes to 500sqft per ton. Getting contractors to HALF the installed size of HVAC systems on newer homes is an uphill battle, especially when the contractors aren't paying the bill.

A much lower cost way to do the above home if you could convince contractors not to oversize would be to install a single 24,000 BTU heat pump and have manual dampers the homeowner could adjust seasonally to direct more/less air to each floor. Not as efficient as the minisplit system you installed, but with such a low load the payback time isn't there with todays power rates. A 2 ton heat pump is about $5k installed in our area, the system you installed would be about 3X that to install. Heating and cooling bills may be 30% more with a conventional system, but that's an extra $30 per month or so with such a low load? The difference is price of the installed systems would never pay back in the systems lifetime. I don't see this changing until our government stops subsidizing energy costs to keep prices low for the consumer.

That leaves comfort, which your system has a huge advantage over conventional design. COMFORT is what HVAC contractors need to be selling in order to get these high end systems selling. People will pay through the nose for high end cosmetic improvements (they have the money) but are unwilling to pay for a HVAC system that is quiet and comfortable. Most people have never experienced a HVAC system that doesn't have large temperature swings, uneven room temperatures, and is so silent you have to mute the TV to heat if it's running. If home buyers knew how comfortable HVAC systems COULD be, they wouldn't accept anything less in their custom/high end home.

Comment by Chris Laumer-Giddens on April 12, 2013 at 7:36am

Bob: Inverter compressors are not "high tech". They've been around for over 30 years in every other part of the world. They're only just now catching on here in the US. There's a small learning curve for most contractors, and once they know how, they love it. 

RE: LOW LOADS: If the equipment isn't matched with the low loads, short cycling (and other discomfort issues) can occur. Yes, even in really tight homes. In fact, there are some cases where, if the load is too small, some systems will stay in fan only mode because the load is too load to call for heating or cooling. This prevents de-humidification because there's no call for cooling the coil. Most conventional equipment can get down to 16,000 - 17,000 btu/h (minimum). The house in this article has 3 zones. Each of them are less than 9,000 btu/h for heating and cooling...and that's at for only 1% of the year. Most of the time, the load is around 2500 - 3500 btu/h, and in the swing seasons, obviously lower. If we try to heat or cool with conventional equipment, it won't remove the moisture in the summer. The capacities are too high. This is where the ability for the inverter compressors to "dial down" to lower capacities helps.

Comment by Bob Blanchette on April 12, 2013 at 7:08am

I'd say with a low load house there is less of a need for high tech HVAC systems. As loads lower, payback times become longer vs. a conventional system. It becomes a matter of comfort more than energy savings at some point.

Comment by Chris Laumer-Giddens on April 12, 2013 at 6:42am

Tom, Diane, Ted, Guy and Joseph:

Thanks for the comments. Very cool stuff, and some of it pretty darn sophisticated. It's been like an experimental house with some of the techniques and systems that we're using. This is the first time for both the LG mini-splits, and the Zehnder ERV. I've specified a LOT of Mitsubishi, and used a lot of other ERVs. I'm pleased, so far.

Comment by Chris Laumer-Giddens on April 12, 2013 at 6:39am

@Dennis: Every hole was confirmed via the manufactures "Hole Table". Each manufacturer varies slightly.

We also were able to anticipate where the holes would be because we had the duct design done very early on. The manufacturer was able to confirm that all duct sizes and location were acceptable.


Comment by Chris Laumer-Giddens on April 12, 2013 at 6:36am

@Bob Blanchette: We're using permanent filters (Web Products) in filter grills that are oversized to maintain low static drop. All three systems have a 20" x 20" x 20" return plenum box with an 18 x 18 ceiling grill. All plenums that lead to plenum box are less than 18" long.

COST: Manufacturer, Specifications, and Contractor all have an influence on the price and the end result. Generally, the systems are comparable to zoned split systems. I've seen some much higher and some slightly less.

ACCESS: Hatch to the encapsulated attic is in the corner of Flex Room on 2nd Floor.

INDUSTRY: The inverter compressor technology is showing up in equipment from just about every manufacturer. WaterFurnace just came out with their 7 series and a pretty slick Zone Control system that, IMHO, helps give GSHPs more validity in low-load homes. The low-loads can still be too low for the 7 Series, or any other conventional system with an inverter compressor. Mini- or Multi-Split systems (VRF) are the only off-the-shelf system that can dial down far enough to deal with the low-loads that are typical in the different zones (e.g. 2,000 or less) of a low-load house. The tighter and better insulated our homes get, the more we're going to need this technology.

Comment by Dennis Heidner on April 12, 2013 at 1:03am

About the 13th picture down -- the duct runs through the floor joists.  The joists are engineered I beams - with some pretty huge holes cut in them for the duct work.  Did the structural people agree to that? Or is it just a lense/camera optical illusion?

Comment by Bob Blanchette on March 30, 2013 at 11:49am

How is access for service provided for the ventilator and the air handlers? Especially the 9,000 Btuh capacity unit, that will serve the entire second floor where we have 3 bedrooms, 2 bathrooms and a flex space.

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