2 Stage Technology

During a conversation with Sue Smith, the Editor of The Tennessee A/C Insider, I was asked to explain the benefits of two-stage heating and cooling technology.

I asked her what she knew about 2-stage technology as it pertained to her own home. She identified to me that there is a greater need for contractors and their consumers to truly understand this and its value with regards to Comfort, Health, and especially efficiency.

I explained it to her the way I have to countless consumers who have bought them from me in the past.

It is imperative to understand the fact that our homes likely had a manual J heat load calculation performed on them. It is in this, that the true value lies. Our load calculation/manual J, was based on some performance standards; one of them is the use of 95 degree outdoor temperature.

The question that we must ask our selves is, if we are using 95 degrees outdoor temperature to identify what size unit our home needs for cooling, what happens when the temperature falls below this?

The answer is, we can't control the humidity the way we would like. I asked Sue; when you go to bed at night do you like it a little colder, and turn you're A/C down a little?

I explained it the same way I do with consumers during a sales presentation;
50% answer no and 50% say yes I do turn it down/cooler at night before I go to bed. The reality about the need for multi/2 stage equipment rest in the yes answer, about needing to turn it down before bed. The fact is when the outdoor temperature falls below that magic 95 Degree mark, your unit starts its journey into the oversized zone for the evening and stays there until the outdoor temp hits 95 again tomorrow, if it does at all!

The need to turn it down a little represents the fact that as the temp gets cooler outside, the heat load on your home reduces. As it reduces, the thermostat sees less demand to call on the a/c, and the cooling cycles reduce in frequency and duration.

Both result in inadequate dehumidification. As the rising humidity gets the attention of the homeowner in the way of increased discomfort, they make the air a little cooler at the thermostat. This now creates a discomfort driven demand to effect some degree of comfort control by reducing more humidity with the additional call for cooling.

The bottom line is, since the unit is over sized for the majority of the day we have to treat the symptom of higher humidity & lower comfort by making it colder than necessary. Necessary, is the operative word here! If we now realize the over-sized nature of the good old-fashioned 1-stage coolers of the past, we can now embrace the fact that; a 2-stage unit will run at a more realistic size/capacity to the real demands of our homes. Example is a 3-ton home will be made MORE comfortable at a warmer, dryer, temperature for the majority of the day. using only a 2-ton output!

If the seer (Seasonal Energy Efficieincy Rating) is 15 for a 3-ton at full capacity, we now realize several efficiency gains, in the 1st/ lower stage of operation.

1st, a 2 ton is obviously smaller and thus less expensive to run than a 3 ton right!

2nd, the efficiency gains of running in part load also see an increase in SEER, generally 8-13 % . A 15 SEER unit now runs closer to 17-18 seer In first stage!

3rd,the fact that it is running longer with the more appropriately sized, for our reduced load, 1st stage 2 ton, means we are keeping humidity much lower, this is greater comfort right?

And last but not least, if it is less humid, we now are likely to turn the temperature higher to keep from feeling too cold! This means less temperature driven demand. I.E. we used to keep it 74 to feel cool now we keep it at 78 and have the same comfort due to the lowered humidity!

All of the above yield a drastic reduction of energy usage!

Fact is SEER IS OLD SCHOOL with regards to energy efficiency and the Department Of Energy really needs to recognize this.

My wife has a Dodge Charger with a big old HEMI V-8 with 345 Horsepower. Yet we get 25 miles to the gallon as long as we keep our right feet under control. This engine not unlike 2/multi stage a/c units cuts off 4 cylinders to handle the majority of times that we just don't need full power.

Old-fashioned Single stage A/C is a thing of the past and as contractors, it is our responsibility as stuards of energy efficiency technologies, to offer these advances to our customers and to help our energy-addicted country reduce its ever-increasing need for more power.