SOLAR energy to help heat your home?

[cheapbeersucks]

I was wondering, due to the increase in natural gas prices this year if it would be feesable to supplement home with solar energy. I was thinking of building a tightly sealed and insulated box appx 6 feet by 4 feet with reflecting mirrors on the bottom; sealed plexiglass on the top.. The light would be reflected onto iron piping that would be painted black and have a slight circulation of air through or past them by means of an intermittantly running fan. Does anyone know of this currently being used or have anything to add to this? Thanks.

[Phi for All]

Where does your iron piping lead to? Are you heating water in it? Where does the fan blow the warmed air to?

 

I would also recommend checking all door and window seals. Open your dishwasher and oven promptly after you use them to let that heat dissipate into the kitchen (dryer too). Change your furnace filters at least every month during winter. Reverse your ceiling fans so warm air is recirculated more efficiently. Buy an insulation wrap for your hot water heater if you don't already have one.

 

I know someone who used an old stand mirror in his back yard to bring sunshine to parts of his yard where the sun couldn't reach, and I wonder if you could do something like this to angle more sunlight into your windows. You'd have to make sure as the day progresses that you're not fading any furniture or pictures.

[cheapbeersucks]

I have an old fireplace that was gas that is not working.. Theres about 4 inch vent pipes running into from outside that which are currently blocked off.. I would run air in one pipe (cold from indoors) to be circulated through what I think would be a warm box providing that the sun is shining on that day and the insulating properties of the box are adequate... No water would be heated as that would take longer to bring to temp and winter sun can be scarce.. The air would be fed through and/or past the heating pipes.. (Iron can absorb alot of heat in the sun!) I was thinking that it is feesable?

[Phi for All]

You mentioned an intermittent fan? What determines when the fan runs, temperature or timer? Also, you could have some flow problems if your iron pipes aren't 4" like the vent piping.

 

I'm going to move this to engineering so you'll get more suitable responses.

[YT2095]

I was wondering, due to the increase in natural gas prices this year if it would be feesable to supplement home with solar energy. I was thinking of building a tightly sealed and insulated box appx 6 feet by 4 feet with reflecting mirrors on the bottom; sealed plexiglass on the top.. The light would be reflected onto iron piping that would be painted black and have a slight circulation of air through or past them by means of an intermittantly running fan. Does anyone know of this currently being used or have anything to add to this? Thanks.

 

hehehehe

I have one, allow me to recommend Copper 1/4 inch pipe, and use the one way square hollow section double "glassing" polycarb sheeting instead of the plexiglass/perspex stuff.

you do NOT need a fan at all! the idea is Radiant energy and not Convection, use a matte black paint too, AND if you have any packets of silca gell, put those in the box too before you seal it (stops any stray condensation from the environ that you constructed it in from re-appearing).

if you want the convection route, then skip the mirror bit entirely and paint the lot black! that works too

[swansont]

Have you tried Googling? There is no shortage of information on the net.

 

try: passive solar heat

[YT2095]

something else to bear in mind, for the Wood part of the construct, I also recommend pressure treated Marine Ply, idealy 7 ply, although I use mine indoors (my green house) it gets quite Humid in there and Very hot (I grow Chilis), marine ply is ideal, it can take all sorts of "punishment" and still maintain its structural integrity for many years

[Douglas]

Well, you could dig a hole 10 feet deep, install some pipes and a fan, and circulate 55 degree F...heat/cold throughout your house year around.

[insane_alien]

why not further then you could get it nice and toasty. if its deep enough you could also make your own electricit but i don't think you could get the equipment to dig down a few miles

[Externet]

Hi.

Yes, what you describe is commonly used to heat homes. But you do not need mirrors, you need the pipes painted black in a sealed box with a glass cover.

If you circulate air trough the pipes, it will heat the home during the day. If you circulate water, it can be stored hot in tanks and its heat released also during nights.

You can obtain about 1 KWatt/m². Make it 5m x 5m on top of your roof and your home will stay toasty all winter.

Search for "solar heating"

Miguel

[ahoward]

http://ussolarheating.com/

[J.C.MacSwell]

Where does your iron piping lead to? Are you heating water in it? Where does the fan blow the warmed air to?

 

I would also recommend checking all door and window seals. Open your dishwasher and oven promptly after you use them to let that heat dissipate into the kitchen (dryer too). Change your furnace filters at least every month during winter. Reverse your ceiling fans so warm air is recirculated more efficiently. Buy an insulation wrap for your hot water heater if you don't already have one.

 

I know someone who used an old stand mirror in his back yard to bring sunshine to parts of his yard where the sun couldn't reach, and I wonder if you could do something like this to angle more sunlight into your windows. You'd have to make sure as the day progresses that you're not fading any furniture or pictures.

 

What's the rush? The heat will dissipate into the rest of the kitchen eventually.

[insane_alien]

yes, but then it will only heat the house up 0.1*C above 'freezing your nuts off' temperature. opening them will heat it up a bit more though not for as long.

[CaptainPanic]

I would also recommend checking all door and window seals. Open your dishwasher and oven promptly after you use them to let that heat dissipate into the kitchen (dryer too). Change your furnace filters at least every month during winter. Reverse your ceiling fans so warm air is recirculated more efficiently. Buy an insulation wrap for your hot water heater if you don't already have one.

 

I disagree with this. I'll treat three examples separately: oven, dishwasher and dryer.

 

Oven

The heat contained in the oven must go somewhere in order to cool the oven. There are only 2 ways to cool down the oven after you made a pizza: either you heat up the house (heat is lost into the inside of the house) or you directly heat up the outside air or ground. Since most ovens are well insulated, I agree that neither should go really fast with the door closed.

 

But: keeping the door closed does certainly not mean that you automatically lose all heat to the outside air. Especially electric ovens are not in contact with the outside air, so it really does not matter whether you open or close the door. Every joule of energy has to travel through your house to the outside air.

 

It does not really matter if you open or close the oven, unless you have an open fire oven and a chimney (in that case, some heat will disappear through the chimney). But that's really old fashioned technology.

 

Dishwasher

The dishwasher is hot and wet on the inside. If you open it, water will evaporate to cool it down. (Almost all excess heat is put into evaporating water). That energy is returned to your household in the form of heat when the water condenses again. A lot of the water will never condense (assuming you don't live in the Netherlands, where air humidity actually is 100% half the year, and it will condense). So, that energy is lost. It will leave your house through whatever form of ventilation you have.

 

And even if it did condense, it typically condenses on the coldest part of your house. Those are, in general, the parts in direct contact with the cold outside. If you condense water on those surfaces, you're basically heating up the outside air.

 

I have to say that I'm not sure how you're supposed to dry your kitchen stuff if you don't open the dishwasher. But it's bad for the energy bill.

 

Dryer

Because normal hot air dryers (not the condense dryers) have their own ventilation, it might be a good idea to open the door. I wonder however how much air is lost. My dryer has a total negligible air flow to outside when it's done, so it makes no difference. Condense dryers, like an oven, are not in direct contact with the outside, so it makes no difference whatsoever.

 

Conclusion

For ovens and dryers it doesn't make much of a difference whether you open the door or leave it closed. For your washing machine or any other application that is wet on the inside, it is bad for your energy bill to open the door.

[DrP]

hehehehe

I have one, allow me to recommend Copper 1/4 inch pipe, and use the one way square hollow section double "glassing" polycarb sheeting instead of the plexiglass/perspex stuff.

you do NOT need a fan at all! the idea is Radiant energy and not Convection, use a matte black paint too, AND if you have any packets of silca gell, put those in the box too before you seal it (stops any stray condensation from the environ that you constructed it in from re-appearing).

if you want the convection route, then skip the mirror bit entirely and paint the lot black! that works too

 

 

To add to this (I once had to write a leaflet in English for an Indian man who sold these solar powered water heating units) - the copper pipe should be 'squashed' so that instead of a circular x-section you have a flat elipse. Thus - more area at 90 degrees to the incident rays - also - more internal suface area for the transfer of heat to the water from the pipe. - And yes - paint it matt black. You want the piping to be as long as possible over the solar pannel - snaking the whole length, and yes the the pannel should also be metal, black and have as much of it's area in contact with the piping (so any energy it absorbs can also be transfered to the pipes also).

[YT2095]

I watched a neat program on TV a few weeks ago that was all about this group of people that build their own houses out of what would otherwise be seen as Junk, they were almost entirely energy self sufficient as well!

apart from optimal light capture, the main design feature was based around having a high thermal mass to the building, achieved largely by hammering in large amounts of soil and dirt into used car tyres and then using these to build the base of the house with.

it was well funky!

 

aha cool, I just found a link: http://en.wikipedia.org/wiki/Earthship

Edited November 3, 2008 by YT2095

[swansont]

 

Dishwasher

The dishwasher is hot and wet on the inside. If you open it, water will evaporate to cool it down. (Almost all excess heat is put into evaporating water). That energy is returned to your household in the form of heat when the water condenses again. A lot of the water will never condense (assuming you don't live in the Netherlands, where air humidity actually is 100% half the year, and it will condense). So, that energy is lost. It will leave your house through whatever form of ventilation you have.

 

And even if it did condense, it typically condenses on the coldest part of your house. Those are, in general, the parts in direct contact with the cold outside. If you condense water on those surfaces, you're basically heating up the outside air.

 

I have to say that I'm not sure how you're supposed to dry your kitchen stuff if you don't open the dishwasher. But it's bad for the energy bill.

 

[…]

 

Conclusion

For ovens and dryers it doesn't make much of a difference whether you open the door or leave it closed. For your washing machine or any other application that is wet on the inside, it is bad for your energy bill to open the door.

 

Energy is conserved. If the hot water evaporates and then condenses all you've done is move the energy around from the hot area to the cool area, just what you'd expect from the 2nd law of thermodynamics.

 

If, as the context suggests, we're discussing winter, then chances are the air is drier than normal, because cold air has been heated up in your home, and cold air can't support as much water vapor. So you might be doing yourself some good as far as humidifying the house. The alternative of letting the water condense inside the dishwasher and drain means you are letting hotter-than-ambient water move out of your house, which does waste energy.

[CaptainPanic]

Yes, I was assuming we're talking about winter.

 

And yes, you're only moving energy around if you evaporate and condense again. But: you've moved energy to the cold part of the house. Why is that part of the house cold? Because it is a spot that has a good heat transfer to outside. Therefore, if you increase heat transfer to a spot that is itself also good at heat transfer to outside, you've effectively increased the heat transfer from the hot place (dish washer) to outside.

 

I don't see the point of moisturizing the house. To evaporate the water you'll still be spending the same energy, whether you evaporate it from the dishwasher or from a dedicated device. And, if there are any parts in your house are cold, the water will condense there.

 

Just to make the heat balance picture complete:

The other heat effect is radiation (mostly infrared radiation) which originates from any object. Warmer objects lose heat through IR radiation. But it radiates in a random direction (which is better than targeting the coldest part of the house).

 

But it is also true that allowing hot water to leave the house through a drain is another waste. (People generally don't realize that opening a hot water tap is equivalent to turning on a 10 kW machine. Of course that depends on the water flow (liters/second) and temperature of the water - and efficiency of heating).

Edited November 4, 2008 by CaptainPanic

[swansont]

Yes, I was assuming we're talking about winter.

 

And yes, you're only moving energy around if you evaporate and condense again. But: you've moved energy to the cold part of the house. Why is that part of the house cold? Because it is a spot that has a good heat transfer to outside. Therefore, if you increase heat transfer to a spot that is itself also good at heat transfer to outside, you've effectively increased the heat transfer from the hot place (dish washer) to outside.

 

But this is no different than turning on a heater to warm the house up — if one area is better coupled to the outside, you will still transfer that energy.

 

It's also true that water will tend to condense on surfaces that have a large heat capacity. It's not just the coldest points.

 

I don't see the point of moisturizing the house. To evaporate the water you'll still be spending the same energy, whether you evaporate it from the dishwasher or from a dedicated device. And, if there are any parts in your house are cold, the water will condense there.

 

Some people find low humidity to be very annoying. It dries out the skin.

 

 

Just to make the heat balance picture complete:

The other heat effect is radiation (mostly infrared radiation) which originates from any object. Warmer objects lose heat through IR radiation. But it radiates in a random direction (which is better than targeting the coldest part of the house).

 

But it all ends up flowing to the cold region, and trying to get to equilibrium. Cold things radiate, too. They just don't radiate as much.

[CaptainPanic]

But this is no different than turning on a heater to warm the house up — if one area is better coupled to the outside, you will still transfer that energy.

 

It's also true that water will tend to condense on surfaces that have a large heat capacity. It's not just the coldest points.

 

Temperature is the only factor that causes condensation. Close to a cold surface, the air is also cold. This means that the partial vapor pressure of water is lower. That means in turn that the air becomes saturated and even supersaturated with water. So it condenses.

 

The heat capacity (or specific heat, units J/kgK) only means that an object remains cold longer. But if you take 2 objects with identical outer surface area: one colder than the other, but having a lower heat capacity than the other, then the colder object will have a larger initial condensation rate (expressed in mass/time (condensation per time). As it heats up, the condensation will be reduced (the object heats up, vapor pressure increases, supersaturation decreases, condensation reduces).

 

Some people find low humidity to be very annoying. It dries out the skin.

That is a possible reason to humidify the house. Energy savings is not. You might want to try a cream against dry skin. Whether that helps, I don't know (I don't use such creams myself).

Anyway, people in my country don't need humidifiers. We live in a swamp that we drained and now call the Netherlands.

 

But it all ends up flowing to the cold region, and trying to get to equilibrium. Cold things radiate, too. They just don't radiate as much.

 

That is correct. I merely wanted to indicate that additional to the radiation, a mass flow of water vapor introduces a new heat flow.

 

Apologies for hijacking this thread. I think that the topic is important enough though.

[Flashman]

Those pink skinned primate things that typically inhabit your typical dwelling, lose heat through evaporation of water from the skin. Since the purpose of wastefully heating this volume of air is to keep the naked primates cozy, then increasing humidity will decrease the rate at which water can be lost from their skin, thus reducing the rate of heat loss, thus making them more comfortable.

[CaptainPanic]

Those pink skinned primate things that typically inhabit your typical dwelling, lose heat through evaporation of water from the skin. Since the purpose of wastefully heating this volume of air is to keep the naked primates cozy, then increasing humidity will decrease the rate at which water can be lost from their skin, thus reducing the rate of heat loss, thus making them more comfortable.

 

First of all: assuming that we're looking at energy efficiency, not comfort, it would be easier to put on a sweater if you want to be warm. Also, allowing your body to sweat and replacing that heat by for example hot tea is much more efficient than humidifying the entire house.

 

From a theoretical point of view however, I agree that at least the human body should not lose as much heat by evaporation in moist air. However, we've discussed this before: cold wet air feels colder than cold dry air. Why?

 

(So, if you have any ideas - because that particular thread treated a whole bunch of parameters and still had no conclusion - you know where to add that now - probably best to add it in the other thread, not this one).

[Flashman]

But it would be an efficiency issue if you can be comfortable at 19C with 30% humidity rather than 21C with 0% humidity. Then the question would be whether it costs more to maintain 30% humidity vs 2C more temperature differential with the outside walls. However, yes you can go off the other way, 80% humidity at 19C would probably tend more towards "clammy".

[CaptainPanic]

Indeed. I can only agree. And to answer this question, we need to know more about the ventilation of the house. That makes it house-specific... which means we should stop here

[avenir.jim]

The solar air heater works in much the same way as a solar water heater works. The heater is place outside the room in the open so that it can catch the sunlight. It is generally made up of solar panels but people use a variety of things.

I posted a link to a site that sells them but some Mod removed it as spam.

Edited November 19, 2008 by Phi for All
spamvertizinkediten