10427 Air conditioners

I know it’s very un-green and anti-social and makes me officially an Enemy of the Planet and all, but I'm going to publicly confess to having installed an air-conditioning system recently. I thought some people might find our experience interesting, not least because with the summer ending, units may soon be on offer at good prices in Italian electronic and appliance shops.

I feel compelled to say first that the unit we installed is not in the house occupied by me, my partner and our baby daughter, but rather in the apartment used by guests when they come to stay. Since we live here permanently, we have a chance to get used to the heat and humidity of the summer and ceiling fans are generally all we need to be comfortable at night, but it seems to us unfair to expect people from the frozen North (Scotland and The Netherlands, primarily) to come to visit us and suddenly have to cope with the sweltering temperatures of an Italian heat wave both day and night.

This year hasn’t been too bad in terms of prolonged heat, but last summer with its highs in the 40s and night-time lows in the mid-30s left a lasting impression on us. I would not want to subject any friend who was here for a brief break to that sort of discomfort and restless nights.

Coming from Scotland and Holland, we knew very little about air-conditioners when we started looking. I can’t honestly say we know a lot about them now, but we did learn a few things that others might find interesting and helpful if they’re ever considering buying a unit.

First, we discovered that the term for the sort of air-conditioner we wanted was a “split system”. This is as opposed to the combined systems you see in the USA which consists of a box stuck in a window or the often-seen type in Italy which is a medium-sized appliance with an air hose you’re supposed to stick out the window. While we could see how this might be a viable way of getting rid of hot air if you have sash windows and can make up a board with a hole in it for the air exhaust hose, how one might do that in Italy with it’s hinged casement windows was a mystery. Shoving the hose through an open window or door would obviously be a very silly and inefficient way of cooling a space since hot air would be constantly flowing in from outside. Boring a large diameter hole through the wall was a possibility, but that would be a serious undertaking on a old farmhouse with meter-thick walls.

The split system, on the other hand, has the cooling coils, a fan and the controls in the unit inside and the heat-removing coils and a large fan mounted outside. The two boxes are connected with two small diameter copper tubes, a power cable and a control signal cable. There’s also a hose from the inside unit which needs to be taken outside so that water which condenses on the cooling coils can be drained away. Drilling a couple of 30mm holes in a meter-thick stone wall is not trivial, but it’s a lot less serious than trying to put a 100mm hole through.

The system we bought came with refrigerant in the big outside unit, so all that had to be done to install it was hook up pipes between the two boxes, draw a vacuum in the pipes from external unit and the cooling coil, then open up the valves and charge the system. This is not really a DIY job, since the piping requires specialised cutters and formers to make end flanges and not many people have a vacuum pump in their toolbox, but it took our local plumber and his two mates less than three hours to install our system.

There are, I believe, systems on the market which are intended for DIY installation, but I can't mention them by name.

The second thing we learned is that many air conditioners these days are actually reversible heat pumps which can be used to both cool a space during the summer and heat it when it’s cooler. Geotherm has talked a lot here about the efficiency of heat pumps for space heating. While a modern air-conditioner can be a very efficient way of heating, it is an “air source” heat pump system rather than the “ground source” or “water source” heat pump which the systems promoted by Geotherm normally are.

What this means in practical terms is that the coil which is used to dispose of heat from the inside of the building in the summer is air-cooled rather that being buried in the ground or in water. When the unit is used in heating mode, the heat is extracted from the outside air, “concentrated” and moved to the inside of the building.

The positive things about this arrangement are that it’s a lot easier and cheaper to mount a box on the outside of your house than it is to bury hundreds of meters of piping underground or to find a source of running water near your Italian house. The main negative thing about it is that, in the winter when the outside coils are cold, there is a possibility they will frost up and so the system will not be able to function as a heater. The efficiency of extracting heat from the air outside also decreases the colder it gets, so much so that at around −18 °C (0 °F), it actually becomes more efficient to run a normal electric fan heater than it is to use the air source heat pump as a heater.

There can’t be too many places in Italy that get hot enough in summer to really need air-conditioning and also that cold in the winter, so I don’t imagine it will be much of an issue for anyone here. The frosting issue seems to me to be a more likely potential cause of difficulties, but perhaps Geotherm will have comments on how much of a problem it might be in reality given Italian conditions.

The most interesting thing about using one of these air-conditioner units as a heat source in the winter is the efficiency. The unit we bought (LG model S12AM) has a rated normal power consumption in heating mode of 1.2 kW, but a heat output of 4.0 kW. (For techie-minded folk, the equivalent figures are a supply of 5.3 A and an output of 13,648 Btu/h or 3,439 kcal/h. The maximum draw is 8 A or 1,790 kW.)

In other words, one of these units will cut the cost of heating a house using electricity to a quarter of what it would be using a conventional electric heater.

I haven’t even attempted to do the math and try to figure out what that means in real-life-Italian terms and in comparison to other forms of heating such as log or pellet fires, town gas and so on, but my suspicion is that it would compare well. There are, of course, many other factors to consider such as one’s concerns about where and how the electricity is generated, the fact that some of us have their own sources of wood, the dependability of the electricity supply in Italy and the sheer convenience of setting a thermostat to heat up a room rather than messing around with logs, pellets or whatever.

The heat pump means that the system is equally efficient when cooling with a normal input of 1.1. kW resulting in a cooling output of 3.5 kW (12,000 Btu/h, 3,026 kCal/h). The maximum input is 1.4 kW (6.5 A).

The final major thing we learned about modern air-conditioners is what a label reading “Inverter” means. There’s a Wikipedia page [URL="http://en.wikipedia.org/wiki/Inverter_(air_conditioning)"]here[/URL] explaining the technicalities, but essentially, this means that the compressor (the pump that moves refrigerant between the coils and allows it to transfer heat from inside to out or vice versa) is able to run at variable speeds rather than – as was always the case with older air-conditioners – to only be either running at full speed or off.

This means the system can work a bit more intelligently: it senses the temperature of the room, compares the present air temperature with the desired temperature and adjusts its output accordingly. So when the system is switched on in air-conditioner mode and the room is very warm, the system will put out a lot of very cold air, but as the room cools, the temperature of the cooling coils will be allowed to gradually rise and the fan speed will decrease. When the air is at the desired temperature, the unit will run very slowly, just circulating air and cooling it only enough to offset any heat gain in the room (due to appliances, sun shining through window or whatever). In heating mode, it will similarly produce a lot of heat when it senses the room is cold and then gradually reduce the heat output as the air temperature gets closer to the user’s desired temperature.

Supposedly, Inverter technology can result in a 30% improvement in energy efficiency.