If you suffer from hay fever you’ll know what a blessing it is to be able to sit indoors in spring and summer with all the windows and doors shut, keeping the airborne pollen out while still being kept cool and comfortable. Then, in winter, you don’t keep the windows open as you have central heating and it would just let the heat out. In fact, you never need have fresh air in your home again!

And that’s where the problems start.

Air con and central heating can really dry out the air in a house and a lack of moisture in the air can lead to dehydration. You might ask “So what? I’ll just have another glass of water and I’m good!”

But it’s not only you who’s affected by dry air. You might also see:

• Wood shrink and warp meaning that varnish or paintwork can crack and chip, joints become loose, doors and windows start to stick or let drafts in

• Plants drying out and looking unhealthy or even dying because they need watering so much more frequently

• House dust becoming an ever more common problem. Dry air lets dust move about in the air more than moist air does. This means that it can get everywhere more easily making cleaning a harder job than it needs be.

Air conditioning units can become very expensive; if they are set too high or there’s a window open elsewhere in the home, an air conditioner will keep on working until the temperature is reached.

If your air conditioner is the wrong size it won’t work properly, insomuch as one that is too small won’t cool the whole home, just a room or at best a floor in a house while too big a unit will be difficult to control adequately, blasting out too much cold air and becoming a nuisance to adjust correctly.

Another problem that people experience is a health one too, the dry air makes eyes, noses and throats dry, even if you do increase the amount of water you drink. Skin can get dry and scaly while your hair becomes dull and brittle. And these symptoms aren’t restricted to humans, pets will suffer in much the same way, tropical birds which evolved in a particularly humid climate will become especially vulnerable to the effects of dry air.

So what’s the solution?

You could go without your air con. But that means overheating in the summer, a return to the stung eyes, streaming nose and coughing fits of a summer suffering from hay fever. Not really much of a health benefit at all.

The other answer is to consider investing in a humidifier. Now, the idea of having one machine to cool and dry the air and another to put the moisture back in might seem a bit like wearing a belt and braces but all things considered it makes sound sense. Dry air is more of a side effect than an intentional product of the air conditioner and so fixing the problem is something that should be considered. Not only does it make the air feel fresher, it prevents all of the problems listed above, although if things like furniture or antiques are warped it can’t fix them although it can prevent them from getting worse.

Of course they’re not without drawbacks of their own, again, the wrong size of humidifier will prove inefficient, too small and it won’t be able to deal with the space it’s supposed to be humidifying, too big and you run the risk of creating a whole different set of problems with damp and condensation.

Many people might now be considering a portable air conditioning unit for use in the home or office as the nights lighten and the days warm up.   Folk who want to keep cool and reduce their energy consuming carbon footprint in the process are increasingly turning to evaporative coolers.   These use the simple process of evaporation to achieve a cooling effect and while they aren’t as effective as more conventional air conditioning units, they do have the advantage of being far more compact and easier to position as they don’t need an exhaust hose.  The only moving part  that consumes any electrical power is a fan which blows air through a moist fibrous matrix mat,  so they are much more energy efficient.

Evaporative coolers tend to have a large water tank filled with cold water or a mixture of cold water and ice (some models allow you to add more ice).   This water is then fed over a filter mat, air is sucked in through the unit and blown out through the moistened filter and it’s the mechanical process of evaporation that provides the cooling effect – exactly the same as occurs when we sweat.  Because there is no compressor, evaporative coolers are far quieter than air conditioner units, but that same lack of compressor also means that they are not as effective as air conditioners in cooling down a larger room.  Evaporative coolers are less controllable too as they don’t have a method of regulating the air temperature which is being expelled – all you’ll get is cold and a bit colder if you add more ice.  They also need to be in a room with plenty of ventilation otherwise the humidity will rise and the moisture being introduced to the room will cease to evaporate.

To work at their best, they need to positioned by an open window or door.  It’s advisable to have another window or door open on the other side of the room which will push air out and create a good through-flow of air.  Despite all these seeming drawbacks, evaporative cooling appeals to some as it does have much lower running costs than refrigerant based portable air conditioners and evaporative units are certainly much cheaper to buy initially.  The need to have a door or window partly opened to create a “flow-through” effect however may mean they are not the ideal solution for places where there are allergy sufferers and more conventional air conditioning units that can operate with doors and window closed may be the better option.

If you put it in a room with the windows and doors shut, it isn’t going to do much for you apart from circulate air, much the same as a fan, and increase the humidity. In order for evaporative coolers to really make a difference to the temperature in a room, the room needs to be well ventilated.

For every litre of moisture added to an atmosphere approximately 650W of cooling will take place.  However, the higher the humidity, the less moisture will be evaporated as air can only hold so much water at any given temperature. As the air becomes more humid, the cooling effect will be reduced as the air will accept less and less moisture.

So in order to make an evaporative cooler really effective, you have to maintain a low room humidity for the moisture to evaporate and produce the cooling effect. You do this by ensuring the room’s windows and doors are open, and the room has plenty of air flowing through it. As the water in the cooler evaporates, cooling the air and raising its humidity, the humid cool air is pushed out of the room and replaced with warm dry air, which is then cooled and humidified all over again.

By maintaining a good flow of air through a room, the evaporative cooler will work at maximum efficiency.

If possible it is always advisable to position an evaporative cooler by an open window or door so the air is cooled as it enters the room, and have another window or door open on the other side of the room. The internal fan within the cooler will drag air into the room, creating a positive pressure, which will in turn push air out through other open windows or doors.

As well as the evaporative cooling taking place, this simple ventilation will also add to the cooling of a room making it feel more comfortable.

Some evaporative coolers have the ability to add ice to the water tank or incorporate some form of frozen element, which can be put in a freezer and then inserted into the unit. This can significantly increase the cooling effect of the unit.

However, by doing this you do lose some of the low energy benefits of evaporative cooling. Evaporative cooling has much lower running costs than refrigerant based portable air conditioners. However, if you factor in the energy used to chill the ice or freezer element, the running costs will start to increase (probably nowhere near the same level as air con though - although I haven’t done the sums. Anyone wanting to please feel free to leave a comment below and I’ll publish them here).

You do still have the major cost benefit of evaporative coolers being much cheaper to buy initially then portable air conditioners.