heating and cooling

Condenser unit for central air conditioning




Air conditioning – invented 1902 – The human body can work efficiently only in a narrow range of conditions. People give off about 60 Watts of heat continuously into the surroundings, and more during heavy exercise. The temperature of the body is maintained by the evaporation of sweat from the body. For comfort, both the temperature and the relative humidity need to be low.

Conventional air conditioning consists of setting the humidity at an acceptable level, while reducing the temperature. A humidity level of 50% is usually comfortable. The most common method of reducing humidity is to cool the air using a conventional air conditioner. The water vapor condenses and is drained off. Now, the air is very cold, and needs to be heated back up to room temperature before it is released back to the air conditioned area.

Relative humidity – the moisture contained in any given air mass relative to the temperature of that air. Homes have a HVAC device (heat, ventilation, and air conditioning) consisting of an outside unit that contains a compressor and condensing heat exchanger, and an inside air handler consisting of a large fan and evaporator heat exchanger.

In the A/C mode, liquid Freon or equivalent, is pumped into the evaporator in the air handler in the house and is allowed to vaporize. This process will cause the surface of the tubes and fins to get cold. As the big fan takes air out of the living space and forces it through the cold evaporator, the air gives up its heat to the vaporizing refrigerant. The loop continues by pumping the hot vapor outside to the compressor where the heat is squeezed out by compressing the vapor back into a liquid then cooled by a fan in the condensing heat exchanger. If you hold your hand over the unit you can feel the heat being blown out of the heat exchanger. This is the heat that was in the house. The cooled liquid is pumped back into the house and the process starts all over again in a continuous loop. Now this moisture laden warm air from your living area is chilled well below its dew point and the result is that water collects on the evaporator coil and drips down into an internal pan where by gravity, it is piped outside. A “U” shaped trap keeps some water in the pipe at all times to prevent warm outside air from being drawn into the air handler. So we get a lower temperature and a reduction in humidity.

Engineering at home

  • clogged air handler water drain
  • condensate water around a/c drain
  • bleach or drain cleaner “T” access pipe
  • replace air handler filter

The water draining from the air handler is distilled water because it has come from vapor. Distilled water has no contaminants so when it reaches the outside any bacteria or bugs just love it. In hot summer temperatures, this water can turn into thick green pond scum that can block off the draining water. Now the condensate pan can run over and the condensate will head right for the things touching the floor. Carpet, wood floors, cabinets, it all gets wet depending on how long the problem is allowed to go unnoticed.

Most air handlers have a ¾ inch white PVC pipe at the bottom that carries off the condensate. In many installations that pipe goes down into the slab and comes back up outside. That pipe should have a “T” with a cap that allows you to put in some bleach or drain cleaner to keep it sterile. A little cleaner (2 or 3 ounces) often is better than a lot not so often. If your unit doesn’t have a “bleach T”, put one in or have one put in and use it. Many air handlers have an auxiliary pan under the unit that drains in an obvious place so you’ll know when the primary drain is clogged. Some units have a float in the “bleach T” (you will see two wires sticking out of the top) that will shut the unit down if the water backs up enough to float the switch.

To keep the fan from clogging with dust there must be an air filter on the vacuum side of the air handler. The better the filter the more dust it will trap and therefore must be changed more often. Most good filters will last only about 3 months during the air conditioning season. Clogged filters will cause many problems like not passing enough warm house air to keep the coil from freezing. And the more dust and dirt in the filter, the harder the fan motor has to work to get the air through the system. This will reduce capacity and increase the power consumption and less performance. A badly clogged filter can collapse and get drawn into the fan. A reputable A/C service business can do a spring and fall tune up. It’s not that much and it could save a bundle. –Les Lowman Nov12

Heat pump

What’s the problem?

  • Ask – What temperature range is comfortable? Does that change over 24 hours? When do you like it warm? When do you like it cooler?
  • Imagine – What are some ways we have to be comfortable indoors?
  • Plan, Create * Improve

That’s engineering

  • condensation – the reverse of evaporation – that is, when a gas or vapor becomes a liquid, usually by cooling.
  • compressor
  • heat exchange

Engineering ideas

  • humidity, temperature, compression, condensation, heat exchange

Do it
Here are some challenges for you to work on…

  • DIY Air Conditioner – make this air conditioner (or something similar) using inexpensive materials, including some you have on-hand