Thermal Surprise

[Riversong]

Re: Thermal Surprise

Well, Robert, all I can say is that sometimes it's good to rant (even if it might make me look like a fool) if the outcome from my perspective is that I learn something, perhaps learn I may hold erroneous conclusions. I'll take what you've said under advisement, since it's one thing to draw immature conclusions, it's another to tenaciously hold to such even when evidence or facts to the contrary are presented.

Shophound, you may not be a building professional, but your attitude is very welcome here. I've found that many of the veteran contributors (and some of the moderators) cannot tolerate those who correct their misperceptions and instead turn to attack the messenger. The only "fool" is one who cannot learn from their mistakes (I used to tell my outdoor adventure clients that the only failure is not learning from an experience).

from an HVAC perspective, is that the most consistent comfort complaints I hear are from occupants of multi-story residences... I'm seeing a tall, multi-story structure as essentially a habitable chimney...

That's true, though exagerated. Internal delta-P becomes significant in high-rise buildings. In 2-storey homes, the winter ceiling pressure is typically 4-5 pascals (0.1 psf).

For my primary source of income I'm responsible for environmental control of an art museum, where a two story gallery exists, that even with constant air circulation and advanced controls is a challenge to keep rather even temperatures between floors (that have open access to one another).

I suspect that there is a poor thermal envelope with too many windows and inadequate shading.

I know most folks won't tolerate extremes outside the rather narrow ASHRAE envelope for indoor human comfort

That's true, though there is an acceptable range. The summer comfort zone, with 50% RH, extends from 73°F to 79°F. And head-to-toe stratification can be up to 5°F for an 80% satisfaction rating.

I could also mention the legion of HVAC design and installation mistakes that also hamstring this effort.

Which include register location and distribution, duct sizing and flow rate. High wall registers, for both heating and cooling, with low winter fan speeds and high summer fan speeds, provide the least stratification and most comfort.

So, a hypothetical...take a single story rancher with good windows, standard eight foot flat ceilings with a modest vault in the living area...and compare its performance to a two story structure...with nine foot height flat ceilings...and a "great room" whose ceiling height spans between both levels, along with a foyer and staircase that does the same...

Hardly a fair contest with 8' ceilings vs 2-storey open ceilings and 9' room height. But, while the air bouyancy doubles with a doubling of ceiling height, the air leakage rate (ft/sec) increases by about 40% and the natural ACH of the sprawling ranch will be about 40% greater because of the doubling of ceiling area for the same floor area. The more natural infiltration in winter, the more temperature stratification.

Can a two story home have as minimal a gradient in air temperature as I've measured in well weatherized single story structures?

Yes, but only with isolated floors, good air-tight thermal envelope, and well-balanced HVAC systems. Allowing the winter furnace fan to run after thermostat no longer calls for heat helps reduce temperature stratification. It's even possible to reduce stratification with open ceilings with carefully-engineered air-moving systems controlled by differential thermostats.

I haven't touched on the mean radiant temperature aspect, which is another component of indoor comfort levels.

Which is why I don't like forced-air systems - they make it difficult to maintain the human comfort zone in winter when head-to-toe stratification, drafts and low mean radiant temperatures cause grumbling. People like warm feet and cool heads, and the best way to create that kind of reverse stratification in winter is with radiant floors.

[Riversong]

Re: Thermal Surprise

He knows more BS than most builders in North Texas.

Don't let him hear you say that ;-)

[Shophound]

Re: Thermal Surprise

Shophound, you may not be a building professional, but your attitude is very welcome here. I've found that many of the veteran contributors (and some of the moderators) cannot tolerate those who correct their misperceptions and instead turn to attack the messenger. The only "fool" is one who cannot learn from their mistakes (I used to tell my outdoor adventure clients that the only failure is not learning from an experience).

It may be true that I'm not a building professional in the same sense that you are. While I do have extensive history with HVAC systems, building science has been a more recent matter to garner my interest. I've spent considerable time repairing, rehabilitating, remodeling, and even constructing residential structures, so I'm not unfamiliar with your side of things at all. What piques my interest now is merging my HVAC and hands on construction/remodeling experience with building science pertaining to thermal performance in buildings, particularly residential structures.

Regardless, I appreciate your kind words. I've been at this online forum thing since the early nineties, and know forum culture well. I've been guilty myself of being obstinate in the face of contradictory facts, yet grew to realize how much I miss in the process of refusing to yield to evidence not favorable to my all too hastily formed conclusions. Few folks like their sacred cows slain, but if it is what stands between me and becoming more well rounded in my knowledge, break out the sword.

That's true, though exagerated. Internal delta-P becomes significant in high-rise buildings. In 2-storey homes, the winter ceiling pressure is typically 4-5 pascals (0.1 psf).

I measured the delta P between my 8 foot ranch house ceiling and the adjoining attic above the other day. It varied between 1 and 2 pascals. The attic is ventilated and there was a stiff north wind outdoors.

I suspect that there is a poor thermal envelope with too many windows and inadequate shading.

The walls and roof are thick, insulated masonry. The large curtain wall of glass spanning two stories is well shaded except in early to mid morning, and is double pane low e. Nevertheless it is a huge expanse of glass, whose structural members pop loudly when the morning sun strikes it. Regardless, the temperature variance is all day long, as the galleries have lighting, which are all on the upper tier, and generate a good amount of heat. But enough about my museum. Back to homes.

That's true, though there is an acceptable range. The summer comfort zone, with 50% RH, extends from 73°F to 79°F. And head-to-toe stratification can be up to 5°F for an 80% satisfaction rating.

While my education continues along these lines, my initial thoughts are that air temperature, along with humidity, are just two of four factors needed for a person to feel truly at ease, comfort-wise speaking. The surface temperature of one's surroundings also factor in, convective currents being the fourth item (air movement).

I am currently staying in a friend's two story townhome built in the early 80's. Although I brought some of what I call my "thermal snooping tools" along (a Fluke 561 IR thermometer, a Testo H2 temp/RH stick, and a Testo 510 manometer), at first I was hesitant to break them out for fear I would indeed be "snooping" around my friend's house. She turned out to be receptive and curious, and after awhile my snooping revealed serious issues with both her house and HVAC system. My wife and I slept upstairs last night, and this morning we awoke to a room that was 57 degrees, with the baseboards shivering at 48 degrees. An atrocious thermal crime being committed by an envelope poked through with flaws in insulation integrity, thermal bypasses, stack effect, and other offenders. It would take far more time than I care to put here to explain why the HVAC system didn't offset these losses...suffice it to say the installers who changed out my friend's split system HVAC this past summer should be expunged from the trade post haste. I'll tell you one thing...a whirlpool tub along two outside walls with surface temperatures at 48 degrees is not a tub I'd be interested in using during the winter!!

Which include register location and distribution, duct sizing and flow rate. High wall registers, for both heating and cooling, with low winter fan speeds and high summer fan speeds, provide the least stratification and most comfort.

A man who understands the importance of proper air distribution! High sidewall registers are also my preference for year round performance. Unfortunately in my region almost all the registers are in the ceiling, with cheap stamped steel grills that do an absolutely crappy job properly entraining and mixing room air with the supply jet. Door undercuts are the most common return provision room to room, and they often are not enough when doors are closed.

Hardly a fair contest with 8' ceilings vs 2-storey open ceilings and 9' room height. But, while the air bouyancy doubles with a doubling of ceiling height, the air leakage rate (ft/sec) increases by about 40% and the natural ACH of the sprawling ranch will be about 40% greater because of the doubling of ceiling area for the same floor area. The more natural infiltration in winter, the more temperature stratification.

Interesting point you raise concerning amount of ceiling area of a rancher over a two story structure. Hadn't given that as much thought as it warrants. Upon reflection it reminds us that all things are a compromise. Either you sprawl across the planet or go up away from it, with the thermal dynamics of either unique to each (with commonalities to both).

Yes, but only with isolated floors, good air-tight thermal envelope, and well-balanced HVAC systems. Allowing the winter furnace fan to run after thermostat no longer calls for heat helps reduce temperature stratification. It's even possible to reduce stratification with open ceilings with carefully-engineered air-moving systems controlled by differential thermostats.

At first glance, seems like a lot of adjustment for a certain architectural articulation of space. Although my single story rancher is rather modest in size compared to many of its brethren that are considerably larger and more sprawl-ish, it does not require anything more from its mechanical system than to run when heat is required and sit idle when the thermostat has been satisfied. Leaving the blower running between burner operation would accomplish little to reduce temperature gradients, as such is not all that steep.

Nevertheless not everyone prefers single story living, nor does every building site or available real estate in a given location favor such. Therefore when going multi-story we can then discuss how to make it thermally perform well for a comfort and reduced operating cost perspective.

Which is why I don't like forced-air systems - they make it difficult to maintain the human comfort zone in winter when head-to-toe stratification, drafts and low mean radiant temperatures cause grumbling. People like warm feet and cool heads, and the best way to create that kind of reverse stratification in winter is with radiant floors.

Forced air works decently if the envelope is thermally resistant enough to allow the heated air to also heat the surfaces to a comfortable level. We harsh on forced air a lot because common experience with forced air systems is uneven heating, dry air, and noise. Make the structure better at containing the air that has been heated, containing moisture added to the air, and slower at conducting this same heat to the cold outdoors, and the picture changes a bit, yes?

Nevertheless I have found radiant heating where I've experienced it to be WONDERFUL. Cozy from the ground up. Absolutely delightful. Even so, making the envelope less of a thermal robber is paramount for radiant heating to be truly delightful and effective.

[Riversong]

Re: Thermal Surprise

While my education continues along these lines, my initial thoughts are that air temperature, along with humidity, are just two of four factors needed for a person to feel truly at ease, comfort-wise speaking. The surface temperature of one's surroundings also factor in, convective currents being the fourth item (air movement).

Actually, indoor human thermal comfort depends on more than those four. There are two anthropogenic factors:

1. Clothing level
2. Metabolic activity

Six physical elements:

3. Air temperature
4. Mean radiant temperature
5. Radiant asymmetry
6. Air convection velocity
7. Air convection turbulence
8. Air temperature stratification
9. Relative humidity

And one perceptual one:

10. Color (red "feels" warmer than blue)

For evaluation of thermal comfort at a workplace for sedentary activity, ISO 7730 suggests the following requirements:

 Draft Rate <30 fpm winter, <50 fpm summer at neck and ankle.
 Vertical Air Temperature Differences from ankle to head should be less than 3°C (5.4°F).
 Radiant Temperature Asymmetry from cold windows should be less than 10°C (18°F).
 Radiant Temperature Asymmetry from warm ceilings should be less than 5°C (9°F).
 Surface Temperature of floors should be between 19°C and 29°C (66°F and 84°F).
 Relative Humidity should be between 30% and 70%.

...a whirlpool tub along two outside walls with surface temperatures at 48 degrees is not a tub I'd be interested in using during the winter!!

Not indoors, but there's nothing nicer than soaking in my outside wood-fired hot tub on a snowy night.

Door undercuts are the most common return provision room to room, and they often are not enough when doors are closed.

Few builders incorporate jump ducts, transfer grills or return hallway ceiling plenums.

Forced air works decently if the envelope is thermally resistant enough to allow the heated air to also heat the surfaces to a comfortable level... Make the structure better at containing the air that has been heated..and the picture changes a bit, yes?

Yah, but there's also that tendency to want to put ductwork in unconditioned crawlspaces and attics outside the pressure boundary - always, of course, with poorly insulated and leaky ducts!

[Shophound]

Re: Thermal Surprise

Actually, indoor human thermal comfort depends on more than those four. There are two anthropogenic factors:

1. Clothing level
2. Metabolic activity

Yes, what ASHRAE calls the "clo" factor; "clo" for "clothing" level. These two things generally are out of the control of building envelopes and HVAC systems, so I tend to set them aside (but not dismiss them) when discussing the other components, such as what you raise next:

Six physical elements:

3. Air temperature
4. Mean radiant temperature
5. Radiant asymmetry
6. Air convection velocity
7. Air convection turbulence
8. Air temperature stratification
9. Relative humidity

Good points, all. For simplicity's sake I had all of your items above condensed to four catagories:

Air movement (convection velocity, convection turbulence, temperature stratification)

Air temperature

Relative humidity (of which air movement can vary tolerance toward fringes of comfort envelope)

Mean radiant temperature (radiant asymmetry being a component of mean radiant temperature, IIRC)

And one perceptual one:

10. Color (red "feels" warmer than blue)

And there's likely variance within that perception. I react to actual physical components (temperature, humidity, etc.) of my environment more than color, having more acute understanding of said dynamics due to focusing on and studying them. Others, however, may not know such things, but the human mind is associative, connecting "red" with "warmth", for instance.

For evaluation of thermal comfort at a workplace for sedentary activity, ISO 7730 suggests the following requirements:

 Draft Rate <30 fpm winter, <50 fpm summer at neck and ankle.
 Vertical Air Temperature Differences from ankle to head should be less than 3°C (5.4°F).
 Radiant Temperature Asymmetry from cold windows should be less than 10°C (18°F).
 Radiant Temperature Asymmetry from warm ceilings should be less than 5°C (9°F).
 Surface Temperature of floors should be between 19°C and 29°C (66°F and 84°F).
 Relative Humidity should be between 30% and 70%.

Good info...it may be in my ASHRAE Fundamentals book but you just saved me the trouble of looking it up. :)

Few builders incorporate jump ducts, transfer grills or return hallway ceiling plenums.

They don't have to live in what they build, or if they do, they have no clue as to why these things are desirable. Just throw more heat or refrigeration at any comfort problem.

Yah, but there's also that tendency to want to put ductwork in unconditioned crawlspaces and attics outside the pressure boundary - always, of course, with poorly insulated and leaky ducts!

Not unlike commercial buildings with package HVAC on the roof...an entire, thinly insulated, sheetmetal box outside the pressure and thermal boundaries of the structure. Isn't that lovely?

[Riversong]

Re: Thermal Surprise

Not unlike commercial buildings with package HVAC on the roof...

And, even worse, that's how Luke Skywalker was able to access and destroy the Death Star.

[Shophound]

Re: Thermal Surprise

Re: "Death Star" study group effort: LOL!

The weekend in the two story townhome was an educational one for me. First hand experiences with thermal bypasses, uninsulated band joists, stack effect (second floor ceiling pressure of 8 pascals), an abortion of a furnace replacement installation, etc. The info you provided in your previous post concerning radiant temperature asymmetry is timely as I digest what I've observed with my data instruments lately. Again, thanks.

[John B]

Re: Thermal Surprise

I am currently staying in a friend's two story townhome built in the early 80's. Although I brought some of what I call my "thermal snooping tools" along (a Fluke 561 IR thermometer, a Testo H2 temp/RH stick, and a Testo 510 manometer), at first I was hesitant to break them out for fear I would indeed be "snooping" around my friend's house. She turned out to be receptive and curious, and after awhile my snooping revealed serious issues with both her house and HVAC system. My wife and I slept upstairs last night, and this morning we awoke to a room that was 57 degrees, with the baseboards shivering at 48 degrees. An atrocious thermal crime being committed by an envelope poked through with flaws in insulation integrity, thermal bypasses, stack effect, and other offenders. It would take far more time than I care to put here to explain why the HVAC system didn't offset these losses...suffice it to say the installers who changed out my friend's split system HVAC this past summer should be expunged from the trade post haste. I'll tell you one thing...a whirlpool tub along two outside walls with surface temperatures at 48 degrees is not a tub I'd be interested in using during the winter!!

Re: "Death Star" study group effort: LOL!

The weekend in the two story townhome was an educational one for me. First hand experiences with thermal bypasses, uninsulated band joists, stack effect (second floor ceiling pressure of 8 pascals), an abortion of a furnace replacement installation, etc. The info you provided in your previous post concerning radiant temperature asymmetry is timely as I digest what I've observed with my data instruments lately. Again, thanks.

Shophound,
I am still chuckling over the thought of you taking your instruments on Holiday.
You are my new Hero
JB

[John B]

Re: Thermal Surprise

Sounds like you're building a nuclear reactor pressure vessel or a hyperbaric chamber. I know that BS folks like to use this term, but it makes it sound as if there is a significant air pressure difference between inside and outside environments. What we're really talking about is the air barrier

Robert,
I still see merit in remembering that the air control layer is often "under pressure"

[Riversong]

Re: Thermal Surprise

I still see merit in remembering that the air control layer is often "under pressure"

Definitely in a duplex or apartment with the boombox next door!

[Shophound]

Re: Thermal Surprise

Shophound,
I am still chuckling over the thought of you taking your instruments on Holiday.
You are my new Hero
JB

LOL. Well, our friend did not like the news my snooping around turned up, but she was appreciative nonetheless, and overall did not mind my efforts at all. At one time she was trying to sell the place, right when DFW real estate soured, and had to withdraw from the market. Had someone put in an offer and a competent home inspector gone in and seen what I saw, she would have found out then...in the middle of a real estate deal!

Re: air barrier under pressure. You bet it is. Especially if the thermal boundary composition is borderline, like the townhome was. 8 pascals pressure at the second story ceiling plane should not be, pardon the pun, blown off. Yes, a tight structure won't see that kind of differential, but stack effect (as you noted in another thread) is not the only pressure on the structure. Wind is the other major one, obviously.

One thing I would be curious about, John, is how your own thermal envelope performs, given its well insulated nature. Have you considered acquiring an inexpensive IR thermometer and aiming it at your walls, floors, and ceilings to note how it performs in terms of temperature differential? Robert disclosed some vital data on this thread pertaining to radiant temperature asymmetry (RTA). The townhouse was a stark case of RTA, where my Fluke IR read temperatures all over the map in the bedroom we slept in...on one wall! Baseboard low forties and mid to high fifties at ceiling! I would expect a wall built like yours to show much more even temperatures top to bottom and across its breadth than I measured in the townhouse.

Re: TimberCreek performance data...the live energy feed will be interesting once it's available. Yet I'm curious about the thermal performance as well, and would like to see data on that. Good thermal performance leads to energy reduction. Said data would be especially valuable if there's a reasonable way to compare, say, a given wall section built TimberCreek style to a wall section built conventionally, performing under similar conditions on both sides of the wall. Would be hard to accurately nail it if the homes aren't identical, but I'm interested in heat transfer across the wall section itself, something that isn't hard to quantify.

[Riversong]

Re: Thermal Surprise

my Fluke IR read temperatures all over the map in the bedroom we slept in...on one wall!

That's what you get for using a Fluke. It reads only the aberrations ;-)

[Shophound]

Re: Thermal Surprise

That's what you get for using a Fluke. It reads only the aberrations ;-)

That was a rather cheeky reply, Robert! :)

[John B]

Re: Thermal Surprise

One thing I would be curious about, John, is how your own thermal envelope performs, given its well insulated nature. Have you considered acquiring an inexpensive IR thermometer and aiming it at your walls, floors, and ceilings to note how it performs in terms of temperature differential? Robert disclosed some vital data on this thread pertaining to radiant temperature asymmetry (RTA). The townhouse was a stark case of RTA, where my Fluke IR read temperatures all over the map in the bedroom we slept in...on one wall! Baseboard low forties and mid to high fifties at ceiling! I would expect a wall built like yours to show much more even temperatures top to bottom and across its breadth than I measured in the townhouse.

Hey Shop,
Is Shop your first name?
I plan to order the IR-Thermometer very soon....maybe before the end of this year!
I will get back to your other questions/comments soon ...
Happy New Year to ALL

[Riversong]

Re: Thermal Surprise

I plan to order the IR-Thermometer very soon

Amazon.com has several models. The Kintrex IRT0421 is only $45.95, uses AAA batteries, and has a better distance-to-spot ratio (12:1), but lousy ergonomics and a push-button rather than a trigger. The Raytek MT6 ($56.02) and the Fluke 62 ($93.45) have better ergonomics and a trigger (easier to aim), use a 9-volt battery, and are more ruggedly built, but have a 10:1 ratio.

All three have broad temperature ranges, good accuracy, show instant and maximum temps, and come with carrying case and battery. I got the Raytek (which looks identical to the more expensive Fluke, and may be manufactured in the same Chinese plant) and I'm very pleased with it. In fact, it seems to be more accurate for spot readings than the $6,000 unit my fire department uses.