In a usual range of at a needing to heat inside on a 47 to a +5F  outdoors -
Would it be possible to get to a graphical curve or a clear reference of a description at different dropping temperatures of :
What are some heating outputs comparing a highest speed blower stage of usual higher efficiency GEO to highest efficieny AIR heat pumps by a same air temperature at a same air volume and a same air speed then?

what is happening with Geo on a same curve vs air heat pumps as standing alone in an application with out an enrgy loss by a duct loss ? I have an opinion. Commercially- Carrier and other old consoles are still in offices and restauarants in very old resorts; and in warehouses, and in school gymnasiums. Geo Residential consoles are in more literature than those motel heat pumps  and all is in regards to a previous Dana1 and joe.A  discussion:
minisplit web site DOE
www.      nrel.gov/docs/fy11osti/52175.pdf  ( i recommend just copy and paste )

?

I've only seen a handful of geo-air systems up close & personal, and didn't instrument them, but they were all pretty cool in the draft, but the houses were quite comfortable. Most are not modulating systems the way mini-splits are, but many are multi-stage. (This is true of most ducted air-source systems I've seen too.)

It's not hard to design the duct systems to minimize wind-chill from tepid air systems in McMansions, a bit tougher in a 1000' Cape style house.

Dana is correct. Duct systems are often under valued by buyers and code minimum installers yet the root of much dissatisfaction.-

Most systems I deal with are hobbled by poorly performing ductwork

Initially, I was very concerned with low register temps (88 to 90-ish),
but after three seasons, I've forgotten where the supply registers are.
The house is draft-free, and I'm not aware of any location where the
"tepid" heating air blows directly on the carbon units.

OTOH, in cooling mode, I'm acutely aware of the improved comfort.
The old air-source A/C blew freezing cold air from ceiling registers
in the bedrooms. The geo uses the (now forgotten) floor registers,
and it's nearly impossible to tell whether the A/C is running -- but
the thermostat sez the indoor temp is within 1° F of setpoint.

...one thoroughly happy camper,

Looby

Proper register placement and vane angle adjustment are both ill-appreciated aspects of HVAC design and commissioning.

It ain't rocket science - the basic idea is to have supply air "attack the load" which generally means directing supply air at windows and exterior walls while not subjecting occupants to drafts.

Floor registers are not normally ideal sources of cooling air but can function well if properly installed.

90-ish air works fine for heating if care is taken to avoid drafts. Supply air entrians and is diluted by room air, a fact that can work for or against the installer, depending on skill.

It ain't rocket science - the basic idea is to have supply air "attack the load" which generally means directing supply air at windows and exterior walls while not subjecting occupants to drafts.

Is that the best way from an energy efficiency point of view?

Directing warm air right at a window significantly increases the deltaT across the weakest thermal barrier in the room.

It also thoroughly disrupts any air barrier that could possibly form at the glass/room air interface. Air barriers actually contribute to the insulating abilities.

I can see how this might possibly provide for more comfort, but, assuming that people didn't have the backs of their necks directly beneath the window, maybe you'd be better off directing the vents to mix up the air in the room. That way, the windows would "see" an interior temperature closer to room temp as opposed to the 90 degree temp of the incoming heat stream. Less overall heat loss.

Comfort systems have been designed to attack room loads since steam radiators were first placed beneath windows.

The comfort derived reduces drafts and allows occupants to save energy with milder setpoints.

This dialog may contribute to others' suspicions about your possible lack of field experience in these areas.

Posted By engineer on 04 May 2012 07:48 AM
This dialog may contribute to others' suspicions about your possible lack of field experience in these areas.

Too subtle. 

Don't forget that ICFHybrid claims to be an engineer with many houses, so he MUST know what he is talking about. 

I suppose there are a number of strategies that might increase comfort at the expense of efficiency. Oversizing comes to mind.

Is this one of those strategies?

Your theory that it allows a reduced setpoint is interesting, but what about total energy consumption? Any data that might support that?

Don't forget that ICFHybrid claims to be an engineer with many houses, so he MUST know what he is talking about.

Geome, your penchant for making personal attacks where you should address the discussion at hand is well documented. Maybe you should stick to commenting on the material. Unless, of course, you've run out of substance or ability to be more objective. Personal attacks are not wanted here.

Posted By ICFHybrid on 04 May 2012 09:00 AM

Don't forget that ICFHybrid claims to be an engineer with many houses, so he MUST know what he is talking about.

Geome, your penchant for making personal attacks where you should address the discussion at hand is well documented. Maybe you should stick to commenting on the material. Unless, of course, you've run out of substance or ability to be more objective. Personal attacks are not wanted here.

ICFHybrid, a personal attack, really?  You have stated many times that you are an engineer, have many houses, and that you know of what you speak based on this.  Your own words - not mine.

A comment on the material?  Ok, let's take radiant floor heating.  Tubes are often spaced more closely together under windows.  I suppose that's wrong as well in your mind.  Yes/no?

I suppose that's wrong as well in your mind. Yes/no?

I'm not as worried about value judgements as you seem to be. I think the question at hand is whether it supports energy efficiency or not.

A stream of air directed at a window might be what, in the 90's? I don't think tubes in a radiant floor generate anywhere near that sort of temperature differential at the window.

Regardless, the principal is still the same with the radiant tube spacing.

Most people would agree that what's most energy efficient is not always the most comfortable.

Regardless, the principal is still the same with the radiant tube spacing

No, I disagree with your contention that the "principle" is the same, for the reasons I stated, primarily magnitude. Can I assume that you have no further data about whether it contributes to energy efficiency?

Any one who has seen a floor register knows it does not direct air straight in front of it but rather either side? Further a rom with supply and return will mix air regardless of location. Another important reason registers go that by windows is that furniture is likely to go there so those in the know.......
at the end of the day every delivery system has comprimises.

among things not wanted by me here are amatures seeking every oppurtunity to challange a pro's opinion with pet theory de jour.

among things not wanted by me here are amatures seeking every oppurtunity to challange a pro's opinion with pet theory de jour.

See, and I was thinking that one of the nice things about those not working in the trade was that we are willing to ignorantly challenge long standing beliefs like directing air streams at windows and the suitability of radiant and passive solar.

at the end of the day every delivery system has comprimises.

So, is it your position that directing air streams at windows is more a matter of expediency and not so much one of efficiency?

Another important reason registers go that by windows is that furniture is likely to go there

Okay, I'm a bit unclear on that. Registers go by windows because furniture goes there, too?

Directing the air flow at windows makes comfort & window-condensation sense for low performance windows with U values north of U0.34, but adds practically zero advantages with U0.25 & lower windows.

Adding a hard-coat low-E storm window over a U0.34-U0.6 double pane adds more comfort that siting the duct under a window, and is one of many efficiency upgrades that is usually more cost effective than extra geo tonnage to cover the heat loss difference for the lower performance building envelope.

With >=R20+walls and <=U0.25 windows even point-source heating works well, and it hardly matters where registers are located, leading to shorter duct runs.

Comfort is just one reason why I prefer highest-efficiency building envelopes over highest-efficiency heating systems.

But clearly, not being in the HVAC biz I have no idea what I'm talking about (ever!) :-)

leading to shorter duct runs.

So, it sounds like some efficiency could conceivably be gained by not extending duct runs just for the purpose of siting at a window?

for low performance windows with U values north of U0.34, but adds practically zero advantages with U0.25 & lower windows.

I presume that for values in between, the advantage is appropriately indeterminate?

Posted By ICFHybrid on 04 May 2012 12:19 PM

leading to shorter duct runs.

So, it sounds like some efficiency could conceivably be gained by not extending duct runs just for the purpose of siting at a window?

for low performance windows with U values north of U0.34, but adds practically zero advantages with U0.25 & lower windows.

I presume that for values in between, the advantage is appropriately indeterminate?

Depends on climate, average winter temps, etc. In US zone 7 maybe that needs to be modified to "U0.20 & lower windows".  In zone 4 and the warm edge of 5 U0.30 windows don't have much condensation potential and are quite comfortable to sit next to.

The whole radiator-under-the-window thing came about at a time more than a century ago, when windows were single-pane R1.25/U0.8 (on a good day), and leaked considerable air, and the whole-wall performance of most homes was under R5. 

The interior surface temp of a single-pane at 0F outdoor temps is pretty close to freezing, without the radiator/duct placement under the windows you'd get copious condensation or frost.

An R2/U0.50 window has an interior surface temps of  mid 40s to 50F @ 0F outdoor temps- not frost-forming, but still not so cozy.

An R3 window (U0.34, about the performance of a low-E storm over an antique double-hung in good repair, or a low cost "purty-good" low-E replacement window) is already a big improvement on comfort, making the argument for placing the ducts or radiators under the window far less important than it was in 1890.  The wall R of most uninsulated solid masonry houses is less than R3(!). The interior surface glass temp is in the low-mid 50s @ 0F outdoor temps.

At R4 (U.25) the benefit is fading fast.  Even at 0F outdoor temps the interior surface of the glass is ~60F+, and if you have an uninsulated unheated basement/crawlspace the floor could even be colder than the window.  If your mean January temp is +15F, or higher (like most of the US) there are no comfort or condensation rationalization for placement of heat sources under windows.

At R5 (U0.20), fuggedaboudit- that's a better insulating value than the whole-wall-R of most pre-1950 stick-framed houses. If you're sitting by the window at night when its -25F outside you'll still notice, not so much at +10F.

Posted By ICFHybrid on 04 May 2012 10:47 AM
Can I assume that you have no further data about whether it contributes to energy efficiency?

ICFHybrid, you seem to assume a lot.  Where is ANY of your data?

Dana, from what you have posted, it seems as though a vent (supply register) near a window could be beneficial under the right circumstances.  If not beneficial due to windows with an appropriately high U-value, does it then make a difference if the vent is near a window, or not?

Of course, drafts can also be caused by air leaks around any window if it is not installed/sealed properly, even in new construction, so vents near windows could be beneficial.

Having vents near windows could also reduce duct length (i.e. not having to extend ducts beyond windows.)