Comments on: These Ain’t Yer Grandpappy’s Heat Pumps

By: Jean Ankrom

Jean Ankrom — Sat, 10 Jan 2015 20:28:25 +0000

Hello

Hello
This ducted mini heat pump sure has my attention. I live in WV. Below zero right now. I burn coal for a backup. My heatpump is 3 1/2 ton American Standard. I'm getting to old to shovel coal into the stove. Looking for another solution. I'm all electric. Thanks

By: Nate

Nate — Thu, 29 May 2014 01:33:31 +0000
That makes sense, David.
That makes sense, David. Comfort-wise, the occupants fall pretty far to the side of "efficiency and $$$ savings" on the continuum of comfort vs efficiency. This house (mine) is about to begin the process of getting a deep energy retrofit. It's in north-central New Mexico (Albuquerque area), so there are heating and cooling loads. There's already an evaporative cooler which works very well and will probably remain the primary cooling appliance for as long as the weather cooperates. No A/C right now. Grossly oversized 125k BTU 80% gas furnace with bad uninsulated ductwork in an unconditioned attic.

I'm not fixated on the idea of using only a single mini-split, but the way I'm thinking about this is that if I can spend more money on the building envelope in order to downsize the HVAC requirements such that a single ductless mini-split will work--especially as a replacement for the furnace--I'd much rather do that. Of course if a ductless mini-split will never work due to uneven temperature distribution throughout the house, then I'll start looking in the direction of ducted ones or multi-head units with a single compressor.

By: David Butler

David Butler — Thu, 29 May 2014 01:05:04 +0000
Hi Nate. To begin with, I
Hi Nate. To begin with, I would never specify single zone ductless for a two-story home.

A single head may work in a super-efficient ranch home if there's little or no cooling load. A lot depends on the diversity of the design loads. If bedrooms have any significant cooling load, you need direct supply air. Ambient transfer won't cut it. Of course, the main factor that must be considered is homeowner expectations.

Instead of "how to make this work", we should always start with... what's the best hvac solution for this home given all the particulars.

By: Nate

Nate — Wed, 28 May 2014 23:48:43 +0000
A single ductless mini-split
A single ductless mini-split for a high-performance two-story house seems like it's aided by natural convection and the stack effect. How do you think you would make this work in a house with a similarly high-quality building envelope but a one-story ranch layout? Put the unit above the hallway to the bedrooms? Use a ducted unit in a dropped ceiling with very very short ducts to the bedrooms? Give up and use two units--one for the living area and one for the bedrooms at the end of the hall?

By: Steve A

Steve A — Tue, 25 Mar 2014 21:13:34 +0000
I've been living with a
I've been living with a single 1-ton mini-split LG heat pump in my house for some 4+ years now. The house is a conventional wood-framed house from the early 70's. I've dramatically improved the attic and crawlspace insulation, and extensively air-sealed the home (plus added a 40CFM ERV). I haven't used any other sources or auxiliary heating. While it's in the mild Pacific NW, it's worked flawlessly in my 960 sq.ft. house.

I recently installed a similar unit in my brother's newly built, high efficiency home. It also works flawlessly.

By: John Proctor

John Proctor — Tue, 25 Mar 2014 20:11:50 +0000
Enthusiasm is a great thing
Enthusiasm is a great thing and keeps us all going. It also can blind us to the realities when they occur. We recently tested two ductless multi-splits with two heads each. The airflow on high was 52% of specified airflow on one head and 70% in another with clean filters (only two of the four heads were tested). To determine is the only problem was airflow, we forced the full specified airflow through the units and retested. One unit had a maximum COP of 2.9 at an ambient of 68 degrees F -- well below the anticipated COP at that temperature. Unit is rated at 3.44 COP at 47 degrees F ambient.
On top of that the units are controlled by non-adjustable algrythms that appear to be aimed at comfort without apparent regard to efficiency.

By: David Butler

David Butler — Tue, 25 Mar 2014 08:10:06 +0000
@Harris, I don't have Allison
@Harris, I don't have Allison's wit, charm or good looks, but I believe I can clarify the low static issue. I think there may be some confusion.

You're absolutely correct that 'high static' is a bad thing, and you're absolutely correct that you don't need "a lot of velocity" at the supply registers in micro-load homes.

HOWEVER, the available static specification is a hard limitation of the blower. The ducts and filter create the static resistance, using up the available static, if you will. So if ducts and filter exceed the static budget of the blower, then the CFM will drop off, perhaps precipitously. That's obviously a BAD thing. And I can tell you with certainty that 0.12" is barely enough blower power to overcome the static drop for the typical media filter, let alone any elbows in duct run-outs or boots.

If you want to drill down into the specifics of your particular setup, let's do that off-list.

By: Harris Woodward

Harris Woodward — Tue, 25 Mar 2014 07:29:02 +0000
Thanks, Allison. But after
Thanks, Allison. But after watching you blow ping pong balls into the air and scouring the internet, this GC (jack of all trades, master of several) is striking out. High static is obviously bad news, but I don't understand how having too little static pressure is detrimental.

My homes thermal enclosures are topflight (last one was HERS 54 with R-35 walls, R-32 basement, great windows, 1.25ACH50, a 15SEER Carrier HP, electric tankless DHW, NO renewables). So, I'm not sure I need a lot of velocity at the supply registers since perimeter rooms are pretty thermally homogenous.

Can you provide your Allisonian explanation?

By: M.Johnson

M.Johnson — Tue, 25 Mar 2014 02:41:04 +0000
"...although air-source
"...although air-source technology is less efficient than connecting with the ground in theory, he's found the reality to be otherwise..."

I am eagerly looking forward to a future article which gives more facts on this statement.

By: Allison Bailes

Allison Bailes — Tue, 25 Mar 2014 02:10:11 +0000
David B.:
David B.: Thanks for the Alaska paper. I hadn't seen that before.

Thomas D.: We like the ducted mini-split, too.

John N.: If no one was happy, the designers did a poor job. As you know, fixing the enclosure should be the first priority, but even so, you can get hot air from a heat pump. Marc Rosenbaum reports temperature rises of 40 degrees in heating mode, and Harris Woodward in the comment below yours reported nice, hot air coming out of the register.

Harris W.: The word is getting out about ducted mini-splits, but they aren't without their drawbacks. Limited static pressure (sometimes as low as 0.125 i.w.c.) to work with is one. Lower efficiency than the ductless models is another.

John P.: Yeah, that photo's not ideal. I grabbed it from flickr and thought I'd see who mentioned it first. I should probably change it, but sometimes I like to make people nervous. ;~) On the subject of electricity vs. natural gas, your point is certainly a valid one. I think what Richard was talking about was electrifying end uses and then using a lot more solar generated electricity.

Dale S.: Thanks! I didn't catch Jonathan's presentation. Nor did I catch Bruce Harley's talk, but I'll get a chance to hear his at ACI National next month in Detroit.