Search This Blog

Tuesday, 28 June 2011

The difference between a fixed and a portable air conditioner

The process of refrigeration is very simple. A compressor sucks in refrigerant gas at low pressure, and then pumps it out into a section of pipe that ends in a restrictive nozzle, forcing it back into a liquid in the high pressure side, and forcing it back into a gas in the low pressure side. The properties of refrigerant are such that it absorbs heat while at low pressure and gives off heat at high pressure - effecively removing the heat energy from one point and depositing it in another.

This is simple to imagine in a fixed air conditioner, the compressor sits outside and the high pressure part runs throughout the outdoor unit, and the low pressure pipework connects the compressor to the indoor unit. If they are run in heat mode a reversing valve means the compressor runs in the same direction, but the refrigerant is pumped the opposite way around the circuit.

In a monobloc portable air conditioner, it works essentially in the same way. Except the outdoor and indoor unit are contianed within one box. Half of the box is the indoor and half is the outdoor. The pipe circuit is more or less the same, except it is contained within a smaller area - each half has an air intake, so the unit has two grills which are sucking air in, and each half has an outlet - the indoor outlet which simply recirculates into the room, and the outdoor outlet which pushes air down a duct to the outdoors.
The downside of this is that it creates a slight negative pressure in the room where the machine is operating, therefore pulling warm air through doors, vent holes and any gaps which are not air tight.

A more efficient option is the water cooled split portable air conditioner which uses water transfer the heat much like a fixed installation. This therefore recirculates 100% of the air which passes through the indoor unit and does not create the negative pressure, giving more efficiency.

Wednesday, 22 June 2011

Water Cooled Split Portable Air Conditioner or Monobloc Portable Air Conditioner?

The normal standard configuration for a portable air conditioner is a monobloc.  These are a single box, with two air intakes, and two outlets, one outlet for hot air and one for cool air.  Obviously the hot air should be ducted out of the room with flexible or fixed ducting.

The monobloc, or standard type uf unit such as the MCM230 Portable Air Conditioner, a modern, more powerful version of the MCM20 Portable Air Conditioner , the MCM280 Portable Air Conditioner a more powerful version still, or the 35,000 btu MCM350 Portable Air Conditioner the most powerful portable air conditioner which will run on a standard domestic 13A socket are all great machines.

Smaller domestic, plastic bodied portable air con units tend to only allow ducting of up to two or three metres. The MCM range allow ducting of 7 Metres making them much more flexible, they also have a large water collection tank, making emptying less frequent.

Sometimes you need to duct the hot air further still, it can be done with inline fans and similar, but a better solution is the water cooled split portable air conditioner. This unit is connected by a three pipe, one cable, umbilical to an outdoor unit.  The umbilical can be extended to 30 Metres and carries cold water in, hot water out, power for the outdoor unit and all condensate water.

In addition to the extra distance they can be located within a building, the smaller hole requirements for heat extraction (Ducting vs umbilical hose) and the lack of a requirement to empty the water tank - the water cooled split is more efficient.  Where a monobloc  sucks 100% air into the machine, 50% into the hot side and 50% into the cold side, it only pushes 50% back into the room, while 50% is shoved out the exhaust duct to get rid of the heat.  This negative pressure can cause the room to suck small amounts of warm air through any air holes or doorways or similar.  A water cooled split portable air conditioner however recirculates 100% of the air in the room, 100% goes in and 100% goes back into the room, maintaining a neutral air pressure and stopping the problem of warm air being drawn into the room.

The Water Cooled Split is also a quieter machine.

Portable Air Conditioner or Fixed Air Conditioner?

The first question to consider when looking for air conditioning, is whether to purchase a fixed air conditioner or a portable air conditioner.

For rented properties or offices, you must consult the landlord and get permission to have a fixed system fitted.  The fitting requires some destructive work and brings certain legislation and documentation into play which is ever increasing.  I won't list the rules and regulations here, as they are changing constantly and getting tighter and more rigorous as time goes by.  Even if you own the building the on-going cost of meeting current legislation is a valid concern.

If the landlord is happy to have it fitted then the next consideration is whether or not the cost is justified.  It is possible to move air conditioning systems, however it is expensive, it can cost more than the purchase of the equipment in extreme cases.

The advantages of fixed systems is that they tend to take up no floor space, whether you choose a ceiling cassette or a wall mount.  They can be quieter and more efficient.  With a portable air conditioner you can get some heat radiated back into the room from the exhaust pipe.  You may also have a tank which needs regular emptying as air conditioners pull water out of the air drying as well - this water has to be removed.  Some units have the facility to use a hose or similar to pipe the water directly out in the same way that a fixed unit does.

Another critical issue with fixed systems is the location of the outoor unit.  These can be a little unsightly and on the fronts of buildings, planning permission may be required, on a busy high street an outdoor unit on the front of the building is unlikely to be passed.  An alternative is a monobloc fixed air conditioner which uses an intake and exhaust vent and works in a similar way to a monobloc portable - these require no outdoor unit so may be a good choice where outdoor unit location is a problem.

A key advantage of portable air conditioners is flexibility, you can purchase one to use to cool workers in the office - then transfer it to the server room if one of the fixed units fails. You cam move premises without de-comissioning and re-comissioning the unit, and a new one can be purchased and swapped in if a critical unit fails.