Comments on: Guest Post: The Elephant in the Room—HVAC for High Performance Homes

By: Bob

Bob — Fri, 31 May 2013 07:15:00 +0000

Thomas Dugan good luck on
Thomas Dugan good luck on getting people to downsize off the 500sqft per ton standard, much less go smaller than 1.5 tons. Rarely will you see anything smaller than 3 tons installed in a single family home as the primary cooling system.

Once you get cooling loads down below 2 tons, the payback time for geo makes them impractical for most climates.

By: David Butler

David Butler — Fri, 31 May 2013 07:14:20 +0000

@Thomas, I totally agree that
@Thomas, I totally agree that US companies have some catching up to do. Whenever the application allows, those small high-SEER single zone ductless mini-splits are by far the best bang for the buck in residential HVAC.

But mini-split manufacturers need to pay attention to the unique requirements of the US high performance market. In particular, small ducted AHU's like the Mitsubishi SEZ and Fujitsu ARU don't have enough fan power to supply more than a couple of rooms, and the smallest ductless heads have way too much output at minimum capacity for bedrooms. You can possibly get away with one or two ductless heads in cold-climate homes built to Passive House standards, but not so in a cooling dominated climate.

As for geo, there are indeed water source mini-split systems on the market. But instead of routing refrigerant lines to each air handler, it's done with hot and chilled water, and that takes special skills not often found in residential practice. Contact me privately if you want help specifying such a system.

That said, the more efficient you build the shell, the harder it is to justify the most efficient hvac equipment.

By: Thomas Dugan

Thomas Dugan — Fri, 31 May 2013 06:08:21 +0000

I am a builder of hurricane
I am a builder of hurricane resistant homes and that means tight. So now I must also be an energy efficient builder as well. I am an avid supporter of the HVAC industry, but I am frustrated by the lag in the industry in providing smaller systems that are proper for the high efficiency homes that I build. The industry needs to take what has been learned from the mini-split manufacturers and implement those technologies with conventional systems. Specifically the ability to simplify the duct systems by matching multiple air-handlers (zoning) onto single compressor units. This will reduce or eliminate the need for chases and long trunks, thus freeing up valuable floor space. We need small compact 1/2 ton air handlers for bed/bath combinations for instance. My homes spec out at 1000-1400 sf per ton. I need a multi-zone 1 1/2 to 2 ton system. The new ducted mini splits are perfect for this application except I am still limited to an air-to-air system. What about geo-thermal? As we move away from building silly stick-framed houses that are vulnerable to every disaster known to mankind, the need for smaller high efficient systems will grow. It is time for the HVAC industry to pull their collective heads out of their..... "sand piles" and deliver what is needed.

By: David Butler

David Butler — Sat, 20 Apr 2013 00:30:20 +0000

Ryan, I would argue that any
Ryan, I would argue that any inherent difference in distribution efficiency is only relevant to the extent that it impacts operating cost. I would also argue that the challenges in getting forced air systems right have nothing to do with inherent distribution system (in)efficiencies, and everything to do with system design and installation practice, especially the distribution system.

But at least we agree on the direction that HVAC will take as we make the shell ore efficient.

By: Ryan Shanahan

Ryan Shanahan — Fri, 19 Apr 2013 21:19:05 +0000

David, I definitely over
David, I definitely over simplified my statement for sake of posting on a blog. That said, I'm talking about efficiency of distribution not cost.

The "perfect" house in my head has a super shell and utilizes DHP's and HRV's. I think we'll see more of this as we move towards Net Zero.

By: David Butler

David Butler — Thu, 18 Apr 2013 08:33:22 +0000

Bob wrote:

Bob wrote:
...there are few homes of any modern construction that require perimeter mounted registers.

I couldn't agree more.

By: David Butler

David Butler — Thu, 18 Apr 2013 08:30:29 +0000
@Ryan:
@Ryan: That's a pretty bold statement. With all due respect, hydronic radiant is no less complex, and in fact requires even higher skill level than forced air, making it hard to find qualified contractors in many markets. Competitive pricing can't occur in those circumstances.

As for being more efficient (in terms of operating costs), that depends on many factors. For example, if there's no access to natural gas, a heat pump may cost less to operate.

But more importantly, in markets with a significant cooling and latent load, forced air is by far the least expensive solution. Even in dry climates, radiant cooling is a niche market with very few experienced practitioners. Moreover, high efficiency chillers are not cheap.

If builders were willing to spend the kind of money that hydronic radiant typically costs, ES might never have needed to impose those checklists in the first place. And I can assure you, the lack of questions on hydronic source equipment isn't by design. A topic for another day.

As for mini-splits, ducted systems have the same issues as conventional ducted systems. Ductless mini-splits are indeed less complex to design & install, but are limited in application. I use them where they make sense.

By: Bob

Bob — Thu, 18 Apr 2013 07:23:38 +0000
"In high performance
"In high performance homes, there's no need to extend supplies out to the perimeter"

I'd venture to say there are few homes of any modern construction that require perimeter mounted registers. It's a waste of ductwork, and by eliminating this practice ductwork could be easier to implement into conditioned space.

By: Ryan Shanahan

Ryan Shanahan — Thu, 18 Apr 2013 04:48:45 +0000
I like to remind builders and
I like to remind builders and HVAC Contractors that the Version 3 checklists are complicated for a reason: Heating and cooling homes with a forced air distribution system is inefficient in and of itself. The laundry list of checklist items and design requirements are a valid attempt at getting forced air systems to operate efficiently. Move over to a hydronic radiant system or minisplits and the checklists are a breeze. That isn't a coincidence, it's by design.

By: David Butler

David Butler — Wed, 17 Apr 2013 23:36:18 +0000
Armando makes a good point
Armando makes a good point about duct design. Although proper design adds some cost in terms of design time, the duct system itself needn't cost more. In high performance homes, there's no need to extend supplies out to the perimeter, and in many homes, the return duct system can be eliminated entirely (ductless return), which not only reduces fan energy, but is easier to balance if done properly.

In basement homes, a ductless return can also mitigate moisture issues by continuously mixing the air between levels. Isolated basements are a bad idea.