Air-saver-Background Information:

 

Saving Principle

 

1) Air conditioning units are sized for peak load conditons, i.e. for the one or

two hottest days of the year (plus safety margin). In most operational

conditions, the actual loads are a lot smaller, which means that the systems

are oversized. In 99% of the time, they operate in off-design conditions. This

oversizing is a well documented fact/problem in the air conditioning industry.

 

2) Single-Speed systems (majority of window/wall and single split systems,

NOT inverter systems) have no mechanism to match the system’s cooling

capacity to current heat load. (It’s like a sportscar that can only drive at 250

km/h and cannot slow down, no breaks and no throttle). They keep running

on full capacity until the room thermostat is satisfied and turns the system

off.

 

3) In thermodynamic terms partial load means that the air which is blown

across the coils can only take up a small part of the available cooling energy

provided by the compressor. The available cooling capacity is much greater

than the required cooling capacity. This is called “overcooling”.

 

4) Please note that one of the main reason for the market success of variable

speed systems (inverter controlled) and their basis for higher efficiency is

that in contrast to single speed systems they can actually match cooling

capacity and heat load by reducing compressor speed. Oversizing is a much

smaller problem with these units. Also note that - for a number of reasons -

unfortunately there is no reasonable/economical option for retrofitting

existing single speed systems with inverter technology. On large,

commercial systems this can be done, but there is no standard solution and

every system needs to be analysed individually.

 

5) In terms of electric power (which, of course is the savings subject) the

compressor is by far the largest consumer of electrical energy. The fans and

other components play only a very minor role. The compressor typically

accounts for at least 80% (often clearly more) of a cooling system’s energy

consumption, so for energy savings we should focus on the compressor.

 

6) In existing single-speed systems the only way to achieve energy savings

(without changing other system components) is to achieve a higher overall

compressor efficiency. The challenge in this is to determine when to switch 

off the compressor with the smallest possible trade-offs in comfort and

performance.

 

7) Regardless of the heat load, power consumption of the compressor is

constant. The only exception is transient currents when the motor is

switched on. This current is partly transformed into start-up torque, partially it

results in heat losses. However, this effect is very small compared to the

overall quantity of energy we are looking at. So, let’s assume a constant

power intake of the compressor and analyse what happens when the unit

starts and analye overall efficiency.

 

8) Efficiency consideration: It is important to understand that efficieny of a

system is defined as effective output divided by the sum of consumed power.

 

9) When the unit starts, the compressor manages to move a lot of energy into

the coils. The coils can be viewed as an energy storage which is filled up by

the compressor. As long as the compressor manages to push more energy

into the coils (and they in turn become colder (evaporator)), it is working

comparatively efficiently. When thermodynamic saturation is reached, the

coils (in terms of energy storage) are fully “charged up”. In the efficiency

calculation fraction this means that the compressor efficiency worsens since

it is still has the same power consumption but a small output.

 

10) So if energy savings are to be achieved, this is the most suitable point to

switch off the compressor. The stored energy in the system should then be

used up. Once that has happened, the compressor can provide cooling with

high efficiency again and should be switched back on.

 

11) This is exactly what the Air-saver achieves. It optimises the overall

efficiency of the compressor and cuts out the inefficient stages of operation

at partial load. Compared to operation of the unit without the Air-saver, the

percentage of operational time in which the compressors (as the largest

consumer) works with higher efficiency increaseses. This is where the

energy savings are: Less energy is wasted during the inefficient stages

which don’t produce any further cooling effect.

 

12) Simple units cannot do that themselves. They do not even have the required

sensor which is essential to determine thermodynamic saturation. So the

Air-saver transfers the philosophy of load matching from inverter units to

single speed units in the form of an easy and cost effective retrofit.

  

 

 

Measurements

 

Air-saver on/off tests should be done in the form of week-to-week,day-to-day comparison or during the same day, e.g 1.5 hours on, 1.5 hours off etc. Make sure that in the week-to-week or day-to-day comparison the conditions in terms of temperature, humidity, occupants in the room, lighting, etc. are as equal as possible.

KWh measurement should be measured. Less precise, but for comparison purposes still suitable (same unit!) is Ah measurement. Also, runtime of the compressor may be determined. Assuming constant current, this also gives a good indication of the savings.

 

Measurements should be done in partial load conditions.

 

There are two extreme situations where the Air-saver  will not achieve any savings:

 

1) Peak load conditions (since no energy is wasted here).

 

2) Unit is very oversized.In this instance, no thermodynamic satuaration is reached since the thermostat set set temp. is reached very quickly.No savings can be achieved here, either.Please note:In this situation, cooling comfort will most probably be very low before installation of an Air-saver since the unit does not allow for proper dehumidificaion. Thisresults in cool, humid air which many peole find discomforting.