The top chart shows a two-day span of a TS system at work in the heat of summer. The compressor kicks into the two-cylinder mode only at the hottest times of day. The two bottom charts are comparisons of humidity (right) and indoor blower noises (left).
BRISTOL, VA — Now that TS (twin-single) technology has been in the marketplace for a while and consumer response is being combined with field test data, something unusual is being found. People actually feel the difference with a TS system in place.

To recap, Bristol Compressors introduced the TS technology compressor, which uses a special crankshaft design featuring a portable lobe that positions itself to allow operation of two pistons in the forward direction of the rotation.

When the compressor is reversed, the lobe repositions itself at the center axis of the shaft and one of the pistons remains idle. The motor reverses direction by employing inexpensive controls and by using the start winding of the piston as the run winding, and run winding as the start winding.

“We were surprised with the number of comments we’ve had from homeowners who say they’ve noticed increased comfort after a TS system is installed,” said Bristol vice president of business development, Dennis Custance. “That’s exciting, because that’s the ultimate benefit of any hvac system.”

Why would people sense the difference in one hvac system vs. another? After looking at data gathered from testing, there seem to be several factors involved. All of them seem to make a contribution to system performance.

(Left)A two-cylinder compressor has an EER around 11. (Right) By using a 20-Hz controller to match blower speed to a single-cylinder compressor capacity, the TS system properly extracts humidity from the air.

Making Comfort Possible

Hvac system design is a balancing act. You have to size an a/c system so it can handle demand on the hottest days. That can make it too large for most cooling loads. At the same time, the installer has to be careful not to undersize the heat pump so it can provide sufficient heat on colder days.

“Too often you can be faced with a system built on compromises, which results in uneven indoor temperatures, lower energy efficiency, excessive on-off cycling, and less reliable operation,” said Custance.

But TS technology can change this, because it makes it easier to cost-effectively size a system for both hot and cold temperature extremes.

Since the technology lets a single compressor provide two capacities, it can be set up so the system operates most of the time at lower capacity. On extreme days, the extra power kicks in to provide the cooling or heating required. The extreme days, naturally, are when people are more sensitive to changes in indoor conditions.

TS operates mostly on one cylinder (lower capacity), which reduces sound levels and makes it quieter than many systems. It is also possible to reduce indoor blower speeds by half, using a variable-speed motor or a simple 30-Hz inverter control. That further reduces overall sound, indoors and outdoors.

And when the blower motor is reduced, there’s another benefit: The system extracts more humidity (up to 10% more), again enhancing indoor comfort. This may be why TS systems get particular praise in very humid climates.

Since the compressor runs with longer cycles on lower capacity, there are fewer temperature spikes indoors.

Compared to a standard heat pump (green), the same-size TS heat pump (yellow) provides an equal performance in cold weather and operates more efficiently in wamer weather. A "hot" TS heat pump (red) is sized so it has enough capacity to operate at much lower temperatures without electric strip heat.

The ‘Hot’ Heat Pump

Heat pump selection is based on both a/c and heating demand requirements, which presents a compromise that often limits heating capacity (hence customer complaints that heat pumps are “cold”).

Supplemental electric strip heat is often needed. Compressor capacity is reduced as outdoor temperatures decrease. Typically, at about 32°F, supplemental electric strip heat is required to meet heating loads.

A TS heat pump system operates on one cylinder until heating loads demand two-cylinder operation. This reduces unnecessary on-off cycling at higher temperatures and allows the system to increase capacity when temperatures go down.

A “hot” TS heat pump can be sized to handle temperatures lower than 32° without strip heat. That improves comfort when the weather is cold, and makes the system operate better even when heating demands are high.

Most of a TS system’s operating time is in one cylinder mode, where compressor efficiency is up to twice as high. During one-cylinder operation, system balance conditions are lightly loaded, which creates a more efficient operating condition.

Compressor EERs can be twice as high as a non-TS system. Not only is the compressor operating more efficiently, the indoor blower is using much less energy when running at a reduced speed.

TS technology can be applied to any hvac system efficiency level, from 10 to 16-plus SEER. In fact, the simple components and dual capacity of a TS compressor make it easy to incorporate into existing designs, often enabling them to reach new efficiency levels.