Solar attic fan - worth it?

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  • thehardway
    thehardway Solar Expert Posts: 56 ✭✭✭✭
    #32
    Re: Solar attic fan - worth it?

    IMHO, attic vents are not the way to go, solar powered or not. Heat buildup in the attic should and can be prevented by proper insulating and roofing methods. If you have excessive heat buildup address the cause rather than treating the symptom.

    Climate conditions have a major role in how this is best accomplished but powered attic vents are one more way we squander resources due to improper envelope design and materials.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #33
    Re: Solar attic fan - worth it?
    thehardway wrote: »
    IMHO, attic vents are not the way to go, solar powered or not. Heat buildup in the attic should and can be prevented by proper insulating and roofing methods. If you have excessive heat buildup address the cause rather than treating the symptom.

    Climate conditions have a major role in how this is best accomplished but powered attic vents are one more way we squander resources due to improper envelope design and materials.

    This is entirely true, if you add "venting" to the list of things to do properly.
    It's just that in some cases the cost of fixing the problem would be tens of thousands of dollars because the idiots who built the place did such a horrible job that you have to tear the whole top off the house and start over.
    Been there, done that, and they weren't even selling T-shirts. :roll:
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #34
    Re: Solar attic fan - worth it?

    My entire house fits that description, it was built by the first owner (literally) and nothing is straight/level or evenly spaced. They had a huge attic fan attached to a gable vent and it ran well into the evening. We tore out all of the solid soffit and made it soffit venting so convection would occur, plus added another layer of insulation to the floor of the attic - no more need for the fan. At the time we were tearing off the entire exterior of the house so we could extend it out a few more inches to add more insulation and eliminate all of the drafts (which worked great), but I'd imagine just tearing out the soffit and fitting it with soffit venting wouldn't cost more than a grand or two and not ten. Its a fairly easy job.

    Next up will be adding a radiant barrier (Reflectix is one name brand) below the roof sheathing.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • tonystewart
    tonystewart Solar Expert Posts: 54 ✭✭
    #35
    Re: Solar attic fan - worth it?

    My home in South Florida has a Metro Shingle Roof with Metro Smart Attic vents. Color is Birch 31
    http://www.metroroofproducts.com/metroshingle.cfm
    It has continuous soffits and 5 Metro Smart vents on main living area of 3331 sq ft and continuous soffits and 1 Metrosmart vent over 998 sq ft uninsulated garage, both roofs are 6/12 pitch
    I installed one Master Flow thermostat controlled ac powered fan from Home Depot Model PG3X above my three car garage set to 95 degrees. It turns on by 10 am on sunny warm days. It is mounted to the underside of the MetroSmart vent and sealed to it with expanding foam spray.
    We noticed a small (less than 7 degrees) improvement in the unairconditioned garage space. Attic temperature dropped 15 degrees.
    I installed one Master Flow thermostat controlled ac powered fan from Home Depot Model PG3X in the middle vent of main house set to 95 degrees. It turns on by 10 am as well. It is mounted to the underside of the MetroSmart vent and sealed to it with expanding foam spray.
    I installed 2 Master Flow Solar Powered Gable fans Model PG Solar from HomeDepot to the farthest east and west Metro Smart vents, same underside mounting and sealed with expanding foam spray. Each unit has an additional 30 watt solar panel wired in parallel to the 10 watt panel it comes with. I realize the 500 cfm rating is a joke, but I hoped that an additional 30 watts of power would give me a buffer for the ac powered vent fan.
    These 2 fans have delayed the start time of the A/C powered fan in the middle by about 2 hours.
    Kiss Energy Solutions installed radiant barrier directly over the top of my 18 year old R-19 batt insulation in late January. Since this addition the main house attic is quite warm yet the interior house is very cool and the A/C is not running much at all. We had a 3 day period where outside air temp was 83 degrees last week and the A/C set at 78 degrees did not cycle once. In fact it took three days for the house to rise 2 degrees, from 75-77 degrees.
    The garage is much cooler and very easy to work in.
    The radiant barrier installer told me that we would see a decrease in cooling requirements because the fans worked so well at eliminating the attic heat.
    It worked for my home, good luck
    T
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #36
    Re: Solar attic fan - worth it?

    Only thing is can add about powered Attic vents is that you have to be able to lubricate the bearings. Most use sealed sleeve bearings without the ability to lubricate them will only last 2-4 years in the heat.

    I just finished a self imposed Energy audit and cash flow of living expenses. As frugal as I am and looking at every detail, I'm depressed at the ones that I can do little about. My town automatically charges $40 a month minimum for water and sewer and the darn Cable TV is $93. If I could get rid of those two , I'd be great.
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,022 ✭✭✭✭
    #37
    Re: Solar attic fan - worth it?

    Catch rain water, use a composting toilet, go to the library, and get a radio...everything covered;)

    Ralph
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  • russ
    russ Solar Expert Posts: 593 ✭✭
    #38
    Re: Solar attic fan - worth it?

    Hi Ralph - I think there should be a planter box with a garden in it - won't feed much more than a mouse but it can be called a 'garden'.

    Russ
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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #39
    Re: Solar attic fan - worth it?

    You could get rid of the cable and put up an antenna. Also you could put up a small satelite dish and get a lot of free stuff. :Dsolarvic:D
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  • Paul54
    Paul54 Registered Users Posts: 18 ✭
    #40
    Re: Solar attic fan - worth it?

    I've done a little research on this. Often what causes premature failure or lack of performance in an attic fan, be it solar or grid, is a lack of free moving incoming air. A properly vented attic needs very little help from fans. Too often there is not a large continuos soffit vent. Even more common is no, or inadequate ridge venting. The standard ridge vent most roofers install does not allow for enough air flow out. Combine this with too little air intake and your attic gets way too hot. One of the simplest and cheapest remedies is to install a bunch of the small shed roof like cheap metal vents up close to the ridge line. If you have ample intake at the soffits and eaves, when you cut the holes for the vents, the sawdust will fly up in your face. That's how you know your venting is going to work. A slightly sloped roof with un-restricted air flow will move a lot of air all on it's own due to the sun heating the roof. It's about as energy efficient as you can get. Think about it this way, if you are standing out in the hot sun and hold a peice of cardboard over your head, you create some shade and feel much cooler. Now instead of a flat sheet put a box over your head, at first it feels cool, but soon it gets quite hot and humid. The difference is air flow.
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  • skennedy
    skennedy Registered Users Posts: 2
    #41
    Re: Solar attic fan - worth it?

    Your advice on this problem will be greatly appreciated. Here's the situation.....

    Every Christmas season the warehouses just below The Cow Palace in Daly City/San Francisco, California are transformed into the City of London for the Dickens Fair. This year, we had balmy warm weather. With 3,000 to 6,000 people at one time jammed into 300,000 square feet of warehouse space, you can imagine how warm and humid it gets. The performers.... wearing costumes designed for foggy and damp London, working under klieg lights and up on a stage, get really warm. The customers, each of them generating about 3 watts of body heat and some of them overweight and on medication, have a drink or two or three, have some fun, do some dancing and next thing you know, they're horizontal and a paramedic is on hand checking them out. This is bad PR, except that the beer and wine sales subsidize the ticket sales. Big Time. So what is an English gent to do?

    The State of California, which owns the joint, is about broke. The management of the Cow Palace doesn't want to make waves by asking for HVAC project funds because they're scared to death that the place will be razed for mixed use development. And Kevin Patterson, who runs Red Barn Productions, which operates The Dickens Fair, doesn't want to spend a lot of money on a ventilation system which only operates 17 days a year and shouldn't be cutting holes in a roof that isn't his.

    So whaddya think about placing solar attic fans over the gravity ventilators (those silver spinning whirligigs) on the roof ?
    Could they be lifted off and set safely in storage? Are they bolted down from the underside? Are they likely to be frozen up from rust and could they be lubed and restored to operation with a little bit of WD-40 and some automotive wheel bearing grease ?

    Could I remove the gravity ventilator and plunk down a solar attic fan on the circular stack or put about 5 of them in a plastic dog house or plywood enclosure to ride free and clear over the top of the ventilator ? The specs say they're good for 800 CFM max at high noon. If I could pull 4,000 CFM from each stack, that would be great.

    Half of the warehouse building uses gravity ventilators (12) and half of the warehouse was built with a ridge vent design.
    Google Earth gives a pretty good view of the building. I have considered creating a push-pull effect by adding more plug in fans to throw more air into the building.

    Any advice you could offer would be greatly appreciated.

    Sincerely,

    Josiah Packer
    (a solar guy and dancer at Fezziwigg's Tea Warehouse)
    (650) 274-2709
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #42
    Re: Solar attic fan - worth it?

    Well for one thing the whirligig vents don't do anything; they're useless. They spin 'round and make noise and look like something is happening, but in terms of actual ventilation they allow less air to escape than a mere open hole.

    Adding real fans of any type will improve this somewhat, but basically not much because the whirligig will be an obstruction to the increased airflow; some of the effort of the fan will be wasted making the whirligig spin rather than exhausting air. Taking the fake turbines off will be an improvement with or without adding fans.

    So it comes down to: how much modification of someone else's building would you be allowed to do? And how much money can be afforded (as any type of fan costs money)? As for solar vs. conventional powered fans, as you can see by this thread the conventional fans are usually cheaper to buy and operate except in circumstances where installing the conventional fans involves significant wiring.

    You'll have to do some measure and design work to come up with two (or more) plans and cost them out. Including examining how much air flow can be achieved and if that would be sufficient to alleviate the problem. It's just not as simple as "solar is the answer".
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #43
    Re: Solar attic fan - worth it?

    Note that a better value for the heat of a human body is around 100 watts, not 3 watts (from what I have read).

    So, for every 15 people, that is about the amount of heat from a plug-in 1,500 watt electric space heater.

    I probably would start reading and following links from an engineering site such as:

    www.engineeringtoolbox.com/ventilation-systems-t_37.html

    And when you hit some rules of thumbs like:

    http://www.engineeringtoolbox.com/air-change-rate-room-d_867.html

    And find the minimum air change for a room/building is 4x per hour and for:
    Auditoriums 8 - 15

    300,000 sqft * 15 ft roof (guess) * 8 turns per hour = 36,000,000 cuft per hour

    Your 300,000 sq ft / 6,000 people = 50 sqft per person (15-50 sqft per person for a "club/halls/churches/etc.").

    To move that much air (just fan motors, no filters, heaters, A/C, etc.) you are probably looking in the 1 kW (~1.5 horse power) range... But depending on lots of factors, that is really in the 0.5-50 kW range (best to worst case).

    This will not be "addressed" by using solar powered ventilators (which would be more expensive and less effective than just installing a grid powered ventilation system).

    For something this large, and will need building permits/fire inspection (public hall--Fire marshal requirements are getting crazy now in San Mateo County--You cannot even have a lighted candle in a church hall for a Boy Scout ceremony--LED "candles" these days).

    Probably the same folks that setup events (tents, etc.) can set you up with ventilation equipment too (I have seen portable air handling systems).

    Fire, smoke, air movement--All way over my pay grade.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #44
    Re: Solar attic fan - worth it?

    Portable trailer mounted AC units are available to rent, they do it all the time here in AZ. The have several large tent venues here and use them on those.
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