Windmill Direct Heating, Cooling, and other uses

Heating directly

Using a windmill to produce heat directly is simple enough in concept. ..Take a vertical shaft with knobby bits on it that is mostly churning a working fluid within a casing, while also circulating it somewhat. ..At the outlet have a valve to control the rate at which hot fluid gets released, and have that depend on how heated the fluid becomes.

Heaters: …The hot fluid can, of course, be run thru baseboard heaters, else thru a radiator with a variable rate fan blowing air into a room or larger space to be heated. ..However, the erratic nature of wind usually means this is not reliable enough a heat source to be used alone, at least not absent some means of storing heat.

Storing heat

The hot fluid may also be added to a flow of similar fluid coming from a ground loop (geothermal) heating system, in which case the ground is the main source of heat in winter, the wind~heated fluid merely augmenting it. ..The length of piping needed in the ground should then be shorter. Best to have this juncture on a side loop because in summer the direction of flow is reversed.

In summer, when little heating is required, the flow of wind~heated fluid may instead be directed thru the ground loop, hot fluid then losing heat to the ground, which becomes a means of “storing” heat, so to speak.

Instead of a ground loop, a cistern [or group of cisterns] largely filled with gravel or pebbles or cobble~size stones, may serve as a heat reservoir. Likely best to have the spaces filled with working fluid. ..Here wind~heated fluid gets distributed over the top and passes down to the bottom.

Windmill produced cooling

Everyone is familiar with huge wind turbines producing electricity to feed an electricity grid. During hot weather large amounts of electricity get used in running air conditioners. Instead, windmills of modest size can provide such cooling in a different way, which would reduce the use of electricity during hot weather.

The main difficulty with wind is its erratic nature. This should be obvious to everyone, yet how many think only of the installed capacity of those huge wind turbines and not their likely contribution to the grid over a span of many months? After all, their maximum output is typically not sustained for long, while their actual average contribution to the grid, uncertain in timing, may be less than a quarter as much. Moreover, a becalmed turbine may have nearly no output at all over a span of several days, and those might be very hot days with little wind.

A smallish windmill necessarily must have some means of storing its output in order to have a reliable amount of cooling even when the wind barely blows. By smaller is meant a horizontal windmill whose blades are maybe 3m in length. Or it could be a vertical axis machine instead. ..Smaller means visually less obtrusive and thus less likely to provoke opposition to its installation, provided the windmill’s machinery runs quietly.

Hospitals, many office buildings, warehouses and industrial areas, retail malls and residential complexes should all find windmill cooling attractive, since the capital invested is soon enough justified through much lower bills for electricity. The installation will provide cooling for decades to come, so the savings will run on indefinitely.

Window air conditioner

In order to appreciate how windmill cooling works, it is useful to consider how a typical window air conditioner operates. Usually they are vapour compressor types powered by an electric motor that runs for most of each hot day. Air conditioning – at least heavy use of it – is very seasonal. And in lower latitudes that season will be lengthy, of course, with peak electricity consumption occurring sometime then. Here, wide adoption of windmill cooling would reduce the peak.

The operating sequence of a typical air conditioner is as follows: a refrigerant with a low boiling point enters the cooling coils through an expansion valve and becomes a vapour. This takes quite alot of energy in the form of heat extracted from the air being blown over these coils by a fan, hence giving cool ‘conditioned’ air.

Next, the refrigerant vapour within the coils gets sucked into the mechanical compressor which compacts it back into a liquid, and that liquid is hot. Typically, it is cooled by going through coils which give up heat to outside air. The cooled liquid refrigerant is now ready to repeat the cycle by passing through the expansion valve mentioned earlier.

While this is convenient in respect of keeping the components compact in size, having a liquid phase is not actually necessary — for even having a gas compressed, cooled, expanded and ejected provides cooling. Rather conveniently for windmill cooling, air may be that gas.

Windmill providing the cool

Wind is rarely smooth and steady for long, but stronger or less strong, perhaps gusty or turbulent, and the shaft to which a windmill’s blades (vanes) are attached conveys such variation in its rate and force of rotation. An air compressor run by it will produce a variable amount of heated air of a set pressure, controlled by a valve. This is no problem for its use in cooling, and hot air is useful other ways as well. Just make sure the compressor is one that runs quietly, lest it seriously annoy the neighbours.

The compressor could be atop the windmill and is to deliver a variable, usually high, volume of air at not much pressure (under 200 kPa, say 30 psi), which will take away most of the heat generated by the machine. It then will go down the tower in a largish diameter pipe, losing heat along the way, before running some distance laterally, possibly underground, to arrive where it will be expanded, which creates cooling.

Alternatively, the compressor may be located farther down the tower or at its base. And that old-fashioned windmill can be adapted to run a compressor there. Or the mill might be a vertical axis type instead.

In that old style of windmill (shown in the photo above) the rotary motion of the shaft, to which the fan of blades is attached, gets immediately converted into a reciprocating up and down motion of a vertical rod. Originally, it was a very long pump rod to raise water from some distance underground to the surface — or rather, to above a tank into which lifted water flowed.

At the bottom of the rod underground was a cylinder having a close fitting plunger moving up and down in it. As the plunger moved down, water below it passed through a flap valve within it, and as the plunger rose that flap valve closed and the whole column of water within the pipe, from down below to surface above, lifted and the top of it flowed sideways by gravity and dropt into a storage tank.

For compressing air instead of lifting water, that reciprocating motion could operate a piston type of air compressor at ground level, pushing air through a valve on each down stroke. Then the hot compressed air would be cooled before being expanded, which expansion draws heat from what surrounds it there.

Alternatively, the horizontal fan shaft could connect with a rotating vertical shaft, which at the tower’s base makes it similar to a vertical axis windmill. The shaft can run any type of air compressor, of which there are several. ..Here again the hot compressed air gets cooled before going elsewhere to be expanded, providing cooling.

Reservoir of coolness

Typically this expansion will occur within a storage reservoir, such as a well~insulated cistern of very salty water. The reservoir is a store of coolness for use in air conditioning even when the windmill itself is not providing much. The saltiness prevents unwanted biological activity. The air which came from the top of the windmill here exits back into the atmosphere, where it will mingle with air likely less clean than it is.

Cooling a building is by blowing air over cold pipes or coils in which a transfer fluid (or perhaps the salty water of the cistern itself) is flowing and returned to the cistern. The speed of the fan regulates the amount of cooling. The reservoir may be nearer the windmill than the building to be cooled, in which case an insulated pipe will carry the cold fluid to it.

Windmill cooling is but one way to cool the reservoir, for there is another of ancient pedigree. ..Evaporative cooling is the label for it, and a simple example shows how it works: ..Take a jar of water wrapped in a damp cloth and place it anywhere out of direct sunlight, preferably on a window sill. As the cloth dries, the heat absorbed in evaporating the water is drawn from the jar and its contents, so the water in the jar becomes cooled. Re~wetting the cloth continues the process, so the water in the jar can become quite cold. ..Naturally, this works best when the humidity of the air is not high. The ancient Egyptians were likely not the only ancient desert people to have figured this out.

One way of effecting this for the reservoir is to have a small exit fan suck humid air from above the water and blow it outside. This perhaps done only at night when fresh cool outside air enters passively to replace it. Having that air immediately contact the water’s surface is helpful in having its humidity increase.

Air conditioning being seasonal, or at least its use in summer being far greater, some other use of hot air from the windmill at other times seems likely. But that is a different matter, another topic.

Ice Rinks Cooling

A vertical axis windmill such as this is well-suited to providing the cold brine that is typically circulated within the concrete slab on which the ice in an ice rink rests. The reservoir of coolness is here colder, as the brine must be cold enough to create and keep the ice. ..Calcium chloride is usually the salt used as it is effective and inexpensive.

Here a regular compressor with a refrigerant would be suitable, the hot tubing of compressed fluid giving off heat for the building (or a nearby building), then passing thru an expansion valve it cools the brine used for the ice.

The reservoir cooled by the windmill can be an add~on to an existing refrigeration plant, for the most part taking its place as regards the ice, which is typically the largest use for refrigeration…Here, the wind as a means of producing that degree of cold saves in operating expense for the ice rink. The capital cost of the add~on would pay for itself within a few years, and it should last at least a few decades more. ..In short, it is a sound investment, a long~term reduction in electricity use overall.