Insulating Roofs

[SLOBuds]

Check this out Pat:

Fan

I bought one of these last week and received it yesterday. Specs are great.

It comes exactly as shown with a simple bracket. So I will need to build an enclosure and duct to exterior. Plus the needed electrical.

[Pat]

SLO, That looks like some I have in ducts here. Is it a German brand? Looks like mine anyway. I have one like that to supply air to the range hood (totally different one for the exhaust portion.) I have some like that for remoted bathroom exhaust fans so the noise factor is reduced. I have one like that located aboiut 20 feet from the basement range hood for its exhaust.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[SLOBuds]

It's built in Italy. Just read that last weekend - nice to see an Italian product which survived a bunch of labor stoppages.

These models come in varying sizes. I calculated mine to be able to exchange all the air in this particular room within 15 minutes. It's pretty noisy but able to operate on a variable control.

[Pat]

SLO, You realize that a room with say 1000 cuft and a fan moving 1000 cuft of air per minute (depending on aerodynamic considerations for your particular installation) that you will change out about 86% of the air in 5-6 minutes.

A thought experiment: put a teaspoon of milk in a 8 oz drinking glass and set it in the sink under the faucet with the faucet putting out 8 oz every 10 seconds. in ten seconds the glass will be just starting to overflow the milky mixture. It will take several additional units of 10 seconds of overflowing before the milky liquid starts to look really clear, at least 5-6 or about a minute or another 48 oz of water.

The above is a clasical exponential mixing problem.

If you blow fresh air into a room and have an exit port to let air out (partially open window for examnple) the incoming fresh air mixes with the room air and the air going out the window is a mixture of room and fresh air with the percentage of it being fresh air growing non-linearly over time.

If you place the fan near the ceiling and use it to exhaust air and have a window partiallly open to admit fresh air, then you are removing the warmest stale air and filling the room from bottom to top with cooler fresh air (This assumes it is hotter inside than out.)

Another interesting fact: Inrush air pulled in by a fan comes from near the fan and is a slow difuse flow right up till the air goes very near the blades of a standard fan or into the duct of a ducted fan (like your recent purchase.) the air leaving a fan is very strongly directed in an exit stream.

You can confirm this with a vacuum cleaner that allows putting the hose on the output side and a table tennis ball or similar. Using the hose on the suction side you have to get pretty darned close (actual scientific term of relative measurement) to the ball to suck it toward the hose. Now turn the hose around to the outlet side and see how far away you can blow the ball.

Quite a difference. A couple inches on one side vs several feet on the other side. Blowing air into a space feels good to you if you are sweating but the blast of air mixes the fresh and stale air so that the air going out the window is not even close to 100% stale. If the fan is used to exhaust air near the ceiling it removes nearly 100% stale air and doesn't mix the fresh incoming air with the stale so you get a lot better stale air replacement.

Caution: This may be on the mid term.

I have some controllers (similar to light dimmers) that I use to control my duct fans. They have an adjusting screw to set the low end so that turning the control all the way to the slow position doesn't let the fan stop.You can make the slowest setting whatever speed you want, right down to where the fan won't start itself and you have to let it start running before going to the slowest setting. A setting below that isn't useful.

I have this kind of control on my range exhaust and intake blowers. I really need it as the intake air fan is oversized and has to be throttled back. They get lots quieter when you slow them down a bit.

IF you calculated the volume of the room and used the capacity of the fan to get 15 min then depending on whether the fan is blowing or sucking and other aerodynamic considerations you might actually have an effective air exchange rate that is way longer than you calculated. Either way I bet it is an improvement.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[SLOBuds]

Pat, a wonderful journey about air flow. I used manufacturer specs to eyeball the full-room exchange time.

All these things I write about are being done on a small cabin of mine in central California - central coast that is. I've had a great time with all the little projects and (for the most part) consider them cheap therapy.

The little cabin has one room, 600 square feet with cathedral ceilings. My super duper fan is installed on a south-facing wall, about 1/2 the way up. The wall is located on one of the 'tall' parts of the cathedral.

I put the fan in the middle there first, because I had a previous fan exit site there and second, with the intent to vent a small kitchen area in addition to a 'whole house' effect.

My plan is to build a simple soffett which has the lower part stationed over the kitchen cooking area and the upper part very close to the peek of the cathedral ceiling. When the fan is activated, it will pull air from the ceiling and from the middle of that wall.

I might build a way for the 'lower' branch of the soffett to be sealed off, so the fan pulls strictly from the top of the ceiling. Open doors and windows and we should be good to go. Quicklhy.

The house is positened north/south. I probably can duct outside air from the north side (eg, cool air) into the cabin room. That might be a nice touch also. It's much cooler on that north side.

What do you think?

And if I did something silly like that, would you think I should port that to the top of the room or the bottom? (Cool air moves down, but my mightly exhaust fan is pulling from the ceiling.)

[Pat]

Yo! Martin, You got it just about perfect considering the preexisting hole and the plans are just about what I would have suggested.

It isn't too important which side of the house the exhaust is on. I suppose the bearings in the fan would last a couple minutes longer on the cool side but really, you did fine.

Putting up a snorkel to near the peak of the ceiling (highest spot) is a very good idea and will improve performance as you will be exhausting the hottest of the air. Are your stud walls insulated inside the cavities? If not use a cavity for a duct. If you want to hide the snorkel duct you can open a stud cavity and replace F/G batting with some rigid foam and leave yourself an air space. A phony chimney up a wall will hide a duct also.

DO NOT DIRECT a ceiling fan upward in your cathedral space as it will mix the hot air into the rest of the room. A ceiling fan is OK and a good idea but they don't do much for you when you are not in their breeze (summer schedule). Use LOOOONG down rods on any ceiling fan in your cathedral space to get the blades within about 9 ft of the floor (not more than 10 for sure). You may need a special mounting adaptor for slopes above about 25-30 degrees or so. I forget the limit on the variouis brands I checked but I have a 12:12 pitch ceiling and had to buy adaptors from a Casablanca parts distributor. Good for any brand and allow my units to fit on a 12:12 pitch.

For rapid air exchange and minimal stale air storage/mixing you can open windows all the way round but after the heavy lifting is done you can just use the ones on the cool side and be OK.

I assume you get at least 25 degrees F or more difference from daytime high temp to overnight low. With that difference or more you will get a very good whole house cooling effect that will really help. With less delta T it can still be well worth doing.

I have a similar situation as I have a duct fan drawing air from the top of the 15 ft ceiling in the sun room. Right now the control is a wire nut to short the hot to the fan lead or take it off and put it over the hot lead to turn the fan off. It will get a single pole double throw center off toggle switch. I will wire it so that in the center it is OFF... period. In one of the other positions the fan will be thermostatically controlled and in the third position the thermostat is over ridden and the fan is energized all the time.

I have already put this configuration in the sitting room to draw off excess winter heat from a parlor stove to warm the bedroom. I used a t'stat that closes on heat rise, the opposite of a typical heater t'stat although I found one supply house with t'stats that have both styles buillt in. They can be used for close on rise or close on fall.

The duct to the range hood or at least above the stove is another fine idea and the damper to only open it up when using the stove is also just fine. I recommend you use metal duct for the portion handling cooking fumes and leading on to the fan. You can still build a pretty soffit but use a metal duct inside, rectangular if you want/need to maximize flow but don't want a huge soffit to take an appropriately sized round duct. You can buy moderately priced washable filters for range hoods at the Sears repair place in some larger Sears stores and some at separate locations. I'd incorporate those so grease and oil from cooking will not get into the ducting.

I don't recall your professed level of expertise as an electrician so I attached a diagram for wiring a 3 position (center off) toggle switch so you can have fan on, fan off, or T'stat control. Now I have revealed my level of expertise as an artist with MSPaint program. I only show the hot wire. The neutral and ground still go to the fan as they do now. This shows how the hot wire is done with a T'stat and 3 position (center off ) toggle switch. Forgive me if your level is way beyond this and it seems insulting to be shown.

My sisters cabin up between Arrowhead and Big Bear had no insulation as it started life as a summer retreat with no A/C decades before they bought it. Heating it was a challenge. Electric blankets running wide open were not always adequate for sleeping. I prefered to bring my down expedition mummy bag.

I'm sure you do way better than those conditions.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[SLOBuds]

Thanks for the drawing - reminds me of the stickmen that I used to draw as a kid. Just an observation ... I can't even READ my own handwriting.

Regarding ceiling fans, my architect tried to talk me into a bunch of those for our new house. The new house had a 'lantern' at the top for a number of reasons associated with passive dynamics. But anyway - when she suggested that, I asked her what the expected effect would be. I mean, all of the warm air would collect in the lantern and it will be VERY toasty during 110 degree days. Are we suggesting that we mix all of that hot air down with the cooler air around my concrete floors??? (Winter use being another topic.)

Maybe those ceiling fans only mix in the cool stratums - but I doubt it.

My perception was that any need to move cool air in the summer would need to stem from a source close to the ground. Probably like floor fans or such. If needed.

Our friends have a house in Palm Springs where summer heat in 110s and even 120s is common. I visited their place a few weeks back and what those folks do is position fans close to where you are sitting. The air conditioner was set to somewhere in the low-80s which is a little bit on the warm side even with just swimming trunks (or less!) on.

So if you sit down for a while to do work at a computer, they have a small localized fan that creates a comfortable micro-environment. I was surprised at how well it worked and how plesant the environment was.

Martin

[Pat]

Martin, Recall the recent lecture on air flow into and out of the fan with diffuse gentle air flow into the fan and strongly directed airflow coming out? A fan mounted approximately mid level in a tall volume, well, at least not too close to the top, when directing air downward doesn't draw air from very far above itself. So, you get mid level air directed downward. Of course if you run the fan really fast the air stream of the downward flow may bounce around and end up disturbing the hot air at the top of the structure. The main contribution of a ceiling fan, in summer, is to increase evaporation of an occupant's perspiration so running a fan in an unoccupied space is a waste.

None of my fans are smart or magic either and can't select only cool air to move. The smarts required is in placing the fans. If your architect had called for fans on downrods long enough to get the fans out of the hottest air, say something like a blade height of 9-10 feet above the floor or so then they would help cool you when the flow was directed downward and if you run them at moderate speeds the stirring of the hottest upper air would be minimal.

The big box stores quit selling the couplers to join downrods together for greater lengths. I suspect someone didn't tighten one enough and had a mishap (visualize a baloney slicer). Anyway all the big boxes around here quit selling the couplers. SO... I had to make my own 10 foot downrods. I used thickwall electrical conduit (1 inch) but because it was galvanized and at the time I knew of no good source of galvanized primer in less than mullti-gallon cans at really high prices, I covered the conduit with thinwall 1 inch PVC. It was a slip fit and the PVC was cheap and easy to paint to look brass. With 10 ft downrods the extra diameter looks good. I have found good galvanized primer in quarts now but will stay with the PVC covers.

If your architect wanted the ceiling fans iniside the "lantern" or nearly so then it was aesthetics only in summer and could recapture heat in winter. Are any of the windows in the lantern, operable?

About floor fans to move cool air... Don't direct them upwards as they will mix in hot upper air into the lower levels. Ceiling fans running slowly and directed downward with a blade height of about 9-10 feet will generate a comfortable micro-climate and not disturb the hot air at the ceiling or in your lantern.

As I write this my office wall stat says the room is 80 and I am getting chilled as I am sitting under a slow running ceiling fan. The fan is on the lowest speed so I need to raise the temp a few degrees. I am NOT cold natured. I often feel too warm when others are OK or too cool. I have not been working outside very much lately due to 100+ temps (108 yesterday). If I really need to do something I try to start early and be done by an hour after sunup. We need for iRobot company to build an autonomous hovering robot that would hover above you to provide shade and a cooling air flow. It should also contain a cooler for cool drinks.

This place is broken up into several zones and I do not ordinarily run more than one zone upstairs as when unoccupied it would be a waste of electricity. It is not good to throttle a fair sized unit back too much so the zone containing my office also contains a guest bedroom.

About running fans in unoccupied spaces... We do, sort of... We have been running our ceiling fans on the back porch during the day to keep the barn swallows from perching on the blades and leaving mounds of guano on the floor. I have "blipped" the switch to start the fan revolving very slowly and blilpped it again and again to slowly increase the speed. The birds hang on for dear life and lean their heads toward the center of rotation and continue to ride till the fan is switched on at low speed and they then fly off. I think they like it but can't "get on" if the fan is running continuously on low speed.

About your comment regarding your hand writing... I resemble that remark. I virtually never write longhand, nearly always I print all caps, even when receiving Morse code. Even then it isn't always easy to read.

Fan is still on low and the stat says 82 and I am very comfortable.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[SLOBuds]

Well, the lantern story is a bit longer still.

We fell in love with the aesthetics and didn't WANT a fan hanging around in the middle. Yea yea yea, I know there are plenty of other things hanging around in the middle like chandliers, pendants, whatnots. It's just that there were views negatively affected. And to miss out on the air flow lecture, mid-levelish, would have sliced beautiful Cat Canyon by a chopping fan leaf.

The house was non-ducted, in-floor radiant heat. So we really didn't need to get all the warm air downwards during winter. But I did worry a bit about stagnant air. Not in winter but in summer. It was going to be a process of opening everything at night and shutting everything some time in the morning. We had data to show that the house would remain plenty cool through the whole day. But 14 hours of closed doors may have been a little too long for comfort.

One of the funnest things we've done up there is hook up a nice Davis Instruments weather station. I can watch inside and outside temperature to figure out when best to open windows or close them. And it's quite easy to get addicted to weather-condition-watching.

Martin

[Pat]

Martin, Your house is, well, your house and whatever you and your wife do is your business no matter what the sane folks say. [img]/forums/images/icons/grin.gif[/img]

We fell that way about ours. Some folks wonder why we didn't build up on one of our higher locations where the hoiuse would stand out much more. We built it for us. We didn't hide it, just put it where we wanted to get views of multiple ponds and stuff. It is not very noticible from the highway (over a 1/4 mile) and not that easily viewed from the section line where our drive connects.

I started out with a NO DUCTS attitude but A/C of this place without ducts would have been quite a challenge. Of course I think you may be going without A/C. We did when we lived on Point Loma in San Diego.

I have indoor/outdoor thermometer atomic clocks with phase of the moon which provide some entertainment but have been shoping for a much more complete weather station. I want remote wireless sensors so I can put the annemometer where I want without having to have a long cable run to mess with. Maybe you and I are just easily entertained or have a low threshold of entertainment but I will probably be fascinated by a nice weather station. I want the automatic rain gage too. I'm not so sure I need the UV sensor.

Rising warrm air was one of the things I was anxious to monitor first hand in a winter sceanario. I knew that there would be less convection taking heat up to the peak of the cathedral ceiling with in-floor hydronics vice forced air but I wanted to actually experience how much. I was quite pleased to note that if the upstairs zones were not active there was enough heat escapiing and going up there to preserve the plumbing in the coldest of weather (overnight lows of 8 degrees followed by a 0F night) but the temps achieved upstairs were still quite cool compard to comfortable temps if you were going to occupy the zone.

I was very happy with the results. We didn't have ceiling fans and didn't use the propane gas log fireplace. We didn't need to run the heat pump dedicated to the upstairs. I hope to install the fans before winter and finish the fireplace. Actually the F/P is ready to go as soon as I put the logset in it and place the artificial embers. It will be interesting to see what the F/P does besides warm the thermostat and kill the floor heat in the great room... oh... and look pretty.

I recommend an ERV or HRV (Energy or Heat Recovery ventilator) for your needs. Which to use depends on your situation as regards humidity. If you don't have a lot of humidity go with the heat exchanger only version. The one is just a heat exchanger and the other also has a humity transfer element. This can give you a fresh air supply without unduly heating the house. It is an ideal adjunct to a whole house fan arrangement where you cool thle hoiuse at night and close it up in the morning and make it through most or all of the hot day before it cools off outside and you start the cycle again.

I have one operating 24-7. It has multi-speed fan and I run it on low all the time with a humidistat in the master bath that sets the humidity level where the ventilator kicks into a higher speed. A shower or Jacuzzi tub session will kick it up to a higher speed. We also have a duct fan as a booster fan on the exhaust side of the otherwised ballanced flow ventilator. It is controlled by a humidistat in the exhaust duct. If the humidity in the bathroom gets high enough then that stat makes the booster fan come on and really sucks air out of the bathroom till the humidity level drops below that sensor's setpoint. It doesn't come on very often but I am glad it is there for when it is needed.

The ballanced ERV exhausts air from the house and brings in fresh outside air but brings it in through a heat exchanger. In your situation in summer the exhausted house air is cooler that the outside daytime air so the heat exchanger would pre-cool the incoming fresh air. This is a wonderful and very energy efficient system. You get a constant fresh air supply (some folks use timers and don't run them all the time) so you avoid the "sick house" syndrome. Timers aren't really needed if you have a multi-speed fan with a low enough setting.

It is so quiet on low that you can't hear it run unless you cock your head next to an exhause grille and then just barely. Even on high you can't hear it anywhere but right next to an exhaust grille and it is still just a whisper. The fresh air duct can be connected to a return air duct of a forced air heating system but we have it dumping the fresh air high up in the great room where it goes all over the house.

One of these ventilators would elliminate any fresh air concerns with the house closed up and would not unduly impact your temperature control scheme. I think it is an ideal application for your situation.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]