### Image Credits:

1. Chris Laumer-Giddens - LG Squared, Inc.

1.
Jan 17, 2014 9:37 AM ET

by Eric Burhop

Thanks Marc.

Unfortunately your statement: "So at that point you’ve spent more in capital cost than the gas system for similar annual cost." is where I found myself when I started researching our mechanicals. I would really like to get away from gas, but for now and probably until my ROI year of a heat pump/solar system I think the annual costs will be similar.

As for our energy load.... I came to this number using rough calculations from a radiant floor heat design website and a manual J excel spreadsheet I found online. Obviously a professional will be doing these calculations in the near future, but with 4200 sq. ft. of livable space (2100 main floor & 2100 basement) I think I am not too far off (42000 btu/hr = 50000 btu/hr)? We are planning on doing PERSIST wall construction with R-30 walls, R-60 roof, and hopefully a less than 1 ACH which will hopefully equate to much lower energy needs.

Thanks again for the very informative Q&A on a topic/product that, I think, will be gaining a lot of momentum over the next few years.

2.
Jan 17, 2014 1:31 PM ET

Edited Jan 17, 2014 3:01 PM ET.

Thank you Marc and GBA
by aj builder, Upstate NY Zone 6a

Thank you Marc and GBA

This blog follow up idea is the best thing to happen here at GBA.

And the subject for me is covering knowledge I am very much in need of.

Question to any of you that calculate energy use via UA units. Resheck which I just used yesterday for a log home I am the draftsman for is a very easy to use program that outputs au units. It also note that one has passed code and by what percentage. The UA units are listed.

Tell us what formula to use in converting UA units to btus lost per a given delta T for either the whole project UA and for the individual UA units it calculates and lists (walls, floors, windows, etc)

3.
Jan 17, 2014 3:11 PM ET

Edited Jan 18, 2014 7:16 AM ET.

Response to AJ Builder

AJ,
Your questions about AU units have me confused. But I'm guessing that you really want to know about UA, not AU.

UA is used to measure whole-building heat loss in Btu/h°F.

Area x U-factor = UA

UA is defined as the "overall average heat transmission of a gross area of the exterior building envelope."

Multiply the surface area of each exposed component of the building envelope by its U-factor to get its "UA" value. Add up all the UA values to get a total building UA value.

UA units are Btu/h°F.

[AJ: I notice now that you have edited your original question, changing "AU" to "UA." That's less confusing.]

4.
Jan 17, 2014 7:18 PM ET

But Martin, multiplication is commutative...
by Dana Dorsett

...thus UA=AU, and shouldn't be a cause for confusion, nicht wahr? :-)

Rescheck notwithstanding, what most of us really care about during the design phase is the AUF- total of A x U x °F, where °F is the delta between the conditioned space temp and the 99th percentile temperature bin for the site location, since that's the stake in the ground that the heating mechanicals and internal heat sources need to meet.

5.
Jan 17, 2014 7:59 PM ET

Edited Jan 17, 2014 8:01 PM ET.

design temperature is wrong
by aj builder, Upstate NY Zone 6a

Dana, I will never use lowest winter temperatures to determine BTU use. To really save energy that is nuts. Use winter average daytime temperatures.

Don't argue this point. No super insulated home needs to combat the lowest temperatures. Homes can coast till warmer daytime temperatures.

Aj

6.
Jan 19, 2014 8:12 PM ET

Great Post

Thanks Marc!

7.
Jan 20, 2014 11:51 AM ET

99th percentile bin isn't coldest by any means (response to #5)
by Dana Dorsett

Meeting the heat load at the 99% outside design temp is often required by local code and vendors, even though the temperature decay time of high-R houses is such that undersizing by a small amount won't create comfort issues.

In an average year there will be 88 hours of temperatures BELOW the 99% bin, and in colder than average years 100s of hours below the 99% bin. The coldest temp in a given year can easily be 15-25F cooler than the 99% bin, or in a mild year 5F above the 99% bin. During this season's cold snaps a few locations have seen daily high temps that did not reach as HIGH as the 99% outside design temperature for more than 48 hours. If sized EXACTLY to the 99% bin it doesn't take much in the way of auxilliary heating or excess plug load to be comfortable in a high-R house, but the notion that you'll "coast" through that with a heating plant undersized by 10-15% is a bit optimistic.

8.
Jan 20, 2014 12:06 PM ET

Daikin Quaternity is fine for Dallas (response to Marc)
by Dana Dorsett

On the prior blog my suggestion (in response # 7 to Scott Tenney) to look into the Quaternity series isn't much affected by a +14F low end of the capacity tables, given that in Dallas TX the 99% outside design temp is +24F, fully 10F above that number. Even the TX panhandle has design temps in the high-teens. Any location under the high-humidity influence of the Gulf of Mexico would be a candidate.

I would be a bit reluctant to recommend it for New England locations, but it's not out of the question for high-R houses in coastal NJ or Long Island NY where the 99% design temps are in the mid-teens, where the 1% design temps are only in the mid to high 80s, yet with summer time dew point averages in the high 60s.

9.
Jan 20, 2014 2:22 PM ET

Standard A/C vs. Ducted Mini
by Peter L

The efficiency on the ducted mini will always be lower than a ductless mini but I wanted to know is it better to go with a DUCTED mini-split or a STANDARD A/C & Heat Pump setup ? What advantages are there with a ducted mini-split over a standard A/C with ducts?

10.
Jan 20, 2014 4:46 PM ET

re: std AC vs ducted mini
by Keith Ritter

Advantages of ducted mini vs std AC

1) inverter-driven compressors in mini's part one. Inverter-compressors allow widely variable outputs to match load as opposed to two-stage std AC high-end compressors, which improves efficiency and COP's in most operating conditions.

2) inverter-driven compressor in mini-part two. The inverter allow the compressors to "over speed" during extreme low-temp conditions. This allows the mini's to create more heat at lower temperatures than standard units and still have an acceptable COP. This in-turn allows minis to have no electric resistance backup heat for those extreme cold temperatures. Note Marc's anecdote about successful mini-operation down to -15 deg. F.

3) ducted mini's are available in sizes 3/4-ton and up, which better match many NZE home loads than std AC's which start at 1.5 tons and in the higher eff. units, frequently are 2 tons and up.

Disadvantages of ducted mini's vs std AC units

1) lower static pressure capacity, which means short, large ducts, large air filters, etc. They don't retrofit well to an existing std AC duct system. Many US HVAC contractors don't yet "get" mini-ducted units and don't know who to lay out the ducts/grilles to their best advantage.

2) mini's use proprietary thermostats. You can't just go down to Lowe's and pick up a standard programmable T'stat or get other 3rd party control systems. Note that this is slowly changing. Some manufacturers are now incorporating BACNet control protocol options in their units, which allows the units to communicate and be controlled over a very common commercial networked digital control protocol used by numerous control manufacturers. This flexibility could eventually trickle down to the residential level

As an EV owner, too, I see the mini/STD AC comparison similar to comparing a purpose-built EV vs an EV built on an existing ICE platform. The purpose-built EV has everything optimized for efficient electric operation (weight, aerodynamics, battery configuration, etc" vs a EV drive-train that has been thrown into an existing automotive platform. It just works better for doing what the primary goal is - optimal efficiency and comfort by breaking some traditional pre-conceptions on the design.

11.
Jan 21, 2014 11:20 AM ET

Edited Jan 21, 2014 11:23 AM ET.

Design temperatures that lower costs and energy use +
by aj builder, Upstate NY Zone 6a

Dana, I hear you... aside from the codes. going green is going with less. at least to me.

The straight forward way to use less energy is to use less.
The straight forward way to less is to install less HVAC.
The same with water and water heating energy.
The smaller the tanked water heater installed the less water and energy used.
Same with all the rest of the home. A smaller home is greener, basic math and science.

Not you necessarily Dana, but crazy talk to anyone who buys the latest SUV so that their kids and family aren't embarrassingly the talk of the town from dropping off kids at school in an unapproved whatever lessor vehicle. Seems much of this site's discussions center around the needs of the SUV owning 3500sqft homeowners that somehow want to go "green" because it's in the news thinking they should save. How does one justify saving \$500 a year in energy costs when the rest of their spreadsheet is filled with multi thousand dollar expenditures to live the Jone's life in comfort riding on heated leather seats in their SUV that starts remotely while checking one last time to see that our hair is perfect before stepping out the door to be... to be a well off "green conscience" approved member of one's community.

Less is more is simple green.
There a hundreds of ways to deal with a few colder than normal hours or days. Going green means doing anything except sizing an HVAC for it, code or otherwise.

That's my idea of green, though I know not that of most.

12.
Jan 21, 2014 9:37 PM ET

AJ Builder
by Peter L

While smaller is a form of being greener, one must also be careful not to cast stones. There is always someone more "greener" than you. They can find fault even with your minimalist approach. We should embrace all forms of being energy conscience and not cast aspersions that one persons green approach is better than someone else. We can find faults in all approaches and the homeowner with a 3,500 sqft home who is trying to build an efficient home shouldn't be disparaged for doing so.

So yes, less is more and a form of being energy efficient but there are people who even take a deeper approach and could fault you for not being green enough and accuse you of not being a minimalist. They might live in a 500 sqft home and they find your 1,000+ sqft home to be grossly oversized.

The point is that the green/energy efficient movement shouldn't self-cannibalize and shouldn't cast stones at those looking to be more energy efficient.

13.
Jan 21, 2014 9:48 PM ET

To Keith Ritter
by Peter L

Thank you for the information. Would a ducted mini be able to handle 3 medium sized rooms (16x16) or is that too much static pressure for a single ducted mini to handle?

14.
Jan 21, 2014 10:23 PM ET

Less is more and there is no way around that
by aj builder, Upstate NY Zone 6a

Peter, I am not against large homes. Just stating what I see as an obvious fact. Smaller homes, less children, less vehicles etc., is the lowest cost most effective way to being more green than most anything one can do.