CryogenX4 vs. VFDs and Controls: Complementary, Not Competing

Key takeaways

• Fan and pump power varies roughly with the cube of speed, so modest speed cuts produce large savings.
• PNNL measured an average 57% reduction in RTU energy (range 22% to 90%) from advanced controls on 66 units.
• ENERGY STAR cites an average 52% fan energy savings from variable-speed drives in an EPA study (2008 manual).
• Controls and drives reduce run time and speed; an oil-fouling treatment targets heat transfer and friction during the run time that remains.
• Savings from combined measures interact and do not simply add; measure the package.

Variable frequency drives (VFDs, also called variable-speed drives) and controls upgrades are among the best-documented efficiency measures for existing HVAC. They reduce how hard fans, pumps and compressors work when the building does not need full capacity. An internal oil-fouling treatment such as CRYOGENX4 addresses something different: how efficiently heat moves through the coils and how much friction the compressor overcomes while it runs. These measures solve different problems, which is why they are usually complementary.

What VFDs do

A VFD varies a motor's speed by changing the frequency of the power supplied to it. For centrifugal fans and pumps, the affinity laws apply: flow varies with speed, pressure with the square of speed, and power with the cube of speed. DOE's FEMP O&M guide puts it simply: a small reduction in speed produces a very large reduction in power. The ENERGY STAR Building Upgrade Manual gives two examples: running a fan at 80% speed cuts its power to about 51% of full load, and a 10% pump speed reduction cuts pump energy by about 27%.

Measured results back this up. The manual cites an EPA study in which VSDs on fans provided an average energy savings of 52%. It lists representative installed costs (2008) from about $2,500 for a 5-horsepower drive to about $16,000 for a 100-horsepower drive, and notes that VSDs make the most sense on larger motors that run many hours at fluctuating loads. Prices have changed since 2008, so get current quotes.

On chillers, a VSD on a centrifugal compressor improves part-load efficiency compared with inlet-vane control. The same manual cautions that a compressor VSD may not be cost-effective where the chiller spends long periods at very low loads (around 10% of full load), and notes that chillers spend most of their operating hours at 40% to 70% load.

What controls upgrades do

Controls measures change when and how equipment runs: schedules, setpoints, resets, economizer logic, demand-controlled ventilation (DCV) and staging. Cited results:

• Advanced RTU controls. A Pacific Northwest National Laboratory (PNNL) field study retrofitted 66 rooftop units on eight buildings with a controller that added enhanced economizer control, multi-speed fan control and DCV. Normalized annual RTU energy fell between 22% and 90%, averaging 57%. Units larger than 53 kW running more than 14 hours a day had paybacks under three years even at $0.05/kWh.
• Control tune-ups. ENERGY STAR estimates that calibrating sensors, fixing dampers and valves, and correcting schedules can save up to 30% of annual heating and cooling costs.
• Economizers. A properly operating economizer can cut energy costs by as much as 10% of a building's total energy consumption, up to 20% in mild coastal climates, per the same manual, which also warns that malfunctioning economizers often waste more energy than they save.
• Chiller plant setpoints. FEMP notes that raising chilled-water temperature by 2 to 3 degrees F can raise centrifugal chiller system efficiency by as much as 3% to 5%, and lowering condenser water temperature by 2 to 3 degrees F by as much as 2% to 3%.
• Analytics and fault detection. DOE's Smart Energy Analytics Campaign reported median savings of 9% for organizations using fault detection and diagnostic (FDD) software, with typical simple paybacks of one to two years.

What an oil-fouling treatment does

CryogenX4 describes its product as a one-time treatment installed while the system runs. According to the company, there is no downtime, most installs take one day, no modifications are made to the system, and the work is done by trained, certified technicians. The company's description of the mechanism: compressor oil migrates past seals, circulates with the refrigerant and coats internal coil surfaces as an insulating film; CRYOGENX4's polarized molecules lift that oil and return it to the sump, condition the metal surfaces for better heat transfer, and improve the lubricity of the existing oil. CryogenX4 reports energy savings of up to 30% and a typical payback of 12 to 36 months on the treatment, and says the treatment is intended to last for the remaining life of the equipment. Results vary by equipment condition, and savings are not guaranteed.

In plain terms, controls and drives decide how much the system runs; a treatment like this is intended to change how much cooling the system delivers per kilowatt-hour while it runs.

Side-by-side comparison

When to choose which

• Constant-volume fans or pumps running long hours: VFDs are a strong first move.
• RTUs with broken economizers, fixed-speed fans or no DCV: advanced controls, per the PNNL results.
• Equipment running when the building is empty, or fighting itself: schedules and control tune-up, which is low cost and fast.
• Compressors already well controlled but still drawing more power than expected for the cooling delivered: investigate internal causes, including oil fouling.

How to combine them

Controls first, then everything else. Fixing schedules, setpoints and economizers is usually the cheapest energy you will ever save, and it changes the load that every other measure works against. Next, add drives where loads vary. Then, for compressorized equipment whose operating data still show poor heat transfer, consider an internal treatment.

Two cautions. First, savings interact. If controls cut compressor run hours by a third, any percentage improvement in compressor efficiency now applies to fewer hours, so combined savings are less than the sum of the separate percentages. Second, stage the work so each measure can be measured. IPMVP Option B (retrofit isolation with continuous metering on the affected equipment) is well suited to this. See IPMVP options explained.

Drives and controls on the compressor side

Controls also shape compressor efficiency directly. ENERGY STAR's retro-commissioning chapter flags reciprocating compressors that fail to unload at part load, causing unnecessary cycling, which wastes energy and increases the risk of compressor or electrical failure. Many newer rooftop units and chillers have variable-speed or multi-stage compressors that track load more closely. These features reduce how hard the compressor works; they do not change the condition of the heat-transfer surfaces it works against. A compressor running at reduced speed through a coil with an internal oil film is still pushing heat through that film, so the two kinds of measures operate on different parts of the same problem.

What to measure before and after

For drives and controls, the key data are motor kW, speed, run hours and the controlled variable (duct static pressure, differential pressure, damper position). For an internal treatment, the key data are compressor kW, cooling delivered, and refrigerant-side temperatures and pressures at comparable load and weather. Expressing results as kW per ton or EER at matched conditions lets you compare units and months fairly; see kW per ton, EER and COP explained. For chilled-water plants, the same logic applies to pumps, towers and chillers; see water-cooled chillers.

Keeping control savings from drifting

Controls savings are only as durable as the settings behind them. Overrides, temporary schedules that become permanent, and sensors that drift can erase much of the gain within a few years. Fault detection and diagnostic software is one answer: DOE's Smart Energy Analytics Campaign reported median savings of 9% for FDD users with typical paybacks of one to two years. A one-time equipment-level measure does not drift in the same way, but its benefit still depends on the system being operated and maintained properly afterward.

Next step

Pull a month of trend data for your largest units: run hours, fan speed, economizer position, and compressor kW against outdoor temperature. If the controls story is clean but kW per ton is still poor, add those units to a measured pilot. For a ranked list of measures, see efficiency measures for existing buildings.

Frequently asked questions

If I already have VFDs, will a treatment still help?

Possibly. VFDs reduce speed at part load; they do not change internal heat transfer or oil film. Whether a treatment helps a given unit depends on its condition and should be measured.

Which should I do first?

Controls tune-up first, because it is low cost and changes the load every other measure works against. Then drives and equipment-level measures.

Can I add the savings percentages together?

No. Measures interact. A measure that cuts run hours reduces the base that later measures save against. Measure the combined result.

Are the PNNL controller results typical?

They are measured results from 66 RTUs on eight buildings, with a wide range of 22% to 90%. Your result depends on how the units were running before.

Sources

1. Operations & Maintenance Best Practices: A Guide to Achieving Operational Efficiency, Release 3.0 — U.S. DOE Federal Energy Management Program / Pacific Northwest National Laboratory
2. ENERGY STAR Building Upgrade Manual (2008 edition) — U.S. EPA ENERGY STAR, hosted by the Whole Building Design Guide
3. Field Evaluation of Advanced Controls for the Retrofit of Packaged Air Conditioners and Heat Pumps — Pacific Northwest National Laboratory
4. Smart Energy Analytics Campaign Reveals Continued Energy and Cost Savings for Energy Management Information Systems — U.S. Department of Energy
5. International Performance Measurement and Verification Protocol (IPMVP) — Efficiency Valuation Organization