Protecting VFDs from Overheating – HVAC Insider

November 04, 2022

By Jon LaPorta, Pfannenberg United states of america

Variable frequency drives are a hot subject matter. Progress in VFD technological innovation and reductions in cost are driving fast market place adoption. Spectacular strength price savings can produce a payback period measured in months, and VFDs permit exact motor command in many industrial procedure applications.

But VFDs are also warm in the literal feeling: the state-of-the-art electronics pack a lot more semiconductor elements into a smaller variety variable ensuing in additional extreme heat technology. Elevated temperatures degrade functionality, impair operational trustworthiness and shorten assistance lifestyle.

A selection of cooling strategies have confirmed successful, which includes passive air cooling with supporters and warmth exchangers, and energetic cooling with air conditioning and h2o cooling.

However, deciding the cooling load can be a bit bewildering. Calculations are needlessly intricate by a mismatch of devices of measurement. — Imperial models (HP, BTU, CFM) combined with Metric units (Watt) — and the conversion gets missing in translation.

Thus, at Pfannenberg we have produced easy rule-of-thumb guides for deciding upon and sizing VFD cooling answers.

Protective enclosures cause overheating

The simple problem of VFD cooling comes from the actuality that VFDs generally need to be placed in an enclosure to safeguard them from the instant natural environment, and paradoxically, these enclosures trap heat which necessitates protection from overheating.

Standard NEMA 12 variety enclosures are normally specified to protect from popular dangers these kinds of as settling dust, dripping h2o and condensation of non-corrosive liquids. Significantly, highly developed technologies in new VFDs this sort of as fiber optics demand enclosures with more improved levels of defense.

And with the vast scale adoption of VFD technology, a lot of programs demand enclosures specially intended for difficult environments, from climate and effect resistant outdoor enclosures to tightly-sealed stainless metal enclosures for food creation facilities that have to endure hosedown cleansing. As an enclosure will become more sealed it obviously commences to hold in more warmth, thanks to the lessen in passive dissipation, thus producing a much larger cooling problem.

The dimension of the enclosure also matters a terrific offer. Regular enclosure proportions have been dramatically scaled down in current many years, to in good shape in tighter spaces and to economize on the cost of the enclosure. In a massive box — imagine a space the dimensions of a place — the distinction in temperature concerning the floor space and the ceiling place results in a slight airflow termed natural convection. The smaller sized the place, the a lot less objects are capable to advantage from this cooling impact. Without satisfactory airflow, a phenomenon regarded as “hot spots” is a lot more most likely to establish on the area and in the interior of VFDs, wreaking havoc on delicate electronics.

The scaled-down sort element of VFDs and their enclosures contribute to overheating in a further way: a smaller box signifies that a lot less floor place on the exterior is available to transmit warmth to the encompassing air. All of these elements necessitate successful and reliable cooling answers.

Speedy Adoption of VFDs

But initial, let’s move back again from the box and think about the major photo. The strength performance of VFDs is not just great for individual firms, it is also key to addressing climate transform.

Throughout the world, about a quarter of all electrical vitality is applied to source motors in industrial apps. In the U.S., an believed 40 million motors eat 60-65% of all electrical strength. A few quarters of these motors are variable-torque lover, pump and compressor loads, the sorts of programs ripe for the energy effectiveness afforded by VFDs.

Right now, only about 3% of AC motors are currently managed by VFDs, but about 30-40% of new motors set up just about every calendar year have a VFD. According to a 2021 report by Research Dive, the global variable frequency generate marketplace is estimated to mature at almost 5% annually  to $25 billion in 2027.

The electrical power cost savings are extraordinary. VFDs lessen energy use by enabling electrical motors to work at fewer than complete pace. Essential AC induction motors are intended to run at a frequent velocity, but in precise use, velocity demands fluctuate, with whole pace typically employed only about 10% of the time. The inherent inefficiency is noticeable, analogous to working a vehicle motor with the tachometer showing the engine consistently at its highest velocity.

The energy financial savings can be calculated utilizing the Legal guidelines of Affinity: the electrical power drawn is proportional to the cube of the rotational speed. Therefore, slowing a pump or supporter to 75% pace cuts down electrical power usage by virtually 60%, and 50% speed saves almost 90%.

From these efficiency gains, it is essential to subtract the rather nominal electricity squander of about 3% due to heat loss from the VFD. This warmth decline from the VFD is significant to quantify, not for its fiscal affect, which is small in contrast to the in general effectiveness gains of employing the technology, but relatively for the danger that overheating poses to the VFD electronics if the warmth trapped in the enclosure is permitted to exceed suitable temperature limitations.

When to choose passive cooling and when to opt for lively

There are two distinctive types of cooling, the initial getting passive cooling and the second currently being lively cooling, both sorts make the most of The Second Legislation of Thermodynamics which in very simple phrases is that vitality goes from a better resource to a reduced supply. Passive cooling makes use of the purely natural route of heat transfer with the heat going from the bigger temperature resource to the lessen temperature source. A great example of this is filterfans, filterfans go the colder ambient air into and as a result of an enclosure exactly where that air absorbs heat till it is exhausted and the heat dissipates into the setting.

Active cooling demands a resource of energy to be put into the method in get to make a path for heat to transfer. This is commonly performed with the use of a vapor compression cycle, a vapor compression cycle has four significant parts, a compressor, a condenser, a throttling unit, and an evaporator. The cycle starts with the compressor wherever electrical power is place into the process, refrigerant enters the compressor beneath reduced stress and small temperature where by it is compressed which results in the refrigerant to leave the compressor underneath large pressure and higher temperature. Subsequent the refrigerant travels by way of the condenser where by heat is taken out resulting in the refrigerant to turn into a saturated or subcooled liquid. Then the refrigerant passes by means of a throttling product exactly where its tension and temperature fall. Eventually, the refrigerant passes by way of the evaporator where by warmth is absorbed turning it into lessen strain and lower temperature gasoline, in which the cycle can then repeat.

Determining when to use passive and when to use energetic is reasonably easy. If your ambient temperature is reduced than your concentrate on enclosure temperature or you have a supply of passively chilled water, then a passive cooling unit can be applied which is appealing for strength financial savings. Passive cooling uses noticeably fewer power than active cooling, as the passive cooling does not involve energy to be place into the procedure to allow a route for heat transfer. If your ambient temperature is increased than your target enclosure temperature or you do not have a resource of passively chilled  drinking water, then an energetic device has to be applied.

Very simple way to compute cooling prerequisites

In this article is a straightforward way to determine cooling demands for each active cooling and passive cooling approaches.

Lively Cooling Rule of Thumb

VFDs are commonly sized in horsepower (HP) and cooling devices are measured in British Thermal Units (BTU, or BTU/h for BTU hours). But how do you transform from HP to BTU/h?

Listed here is the rule of thumb for air ailment and h2o cooling:

75 BTU/h is expected for each 1 HP

In other phrases, for a 100 HP VFD travel, 7500 BTU/h of cooling is required.

This rule of thumb is derived as follows:

  • 3% of the electrical energy in a VFD is transformed to heat

  • 1 HP = 746 watts

  • 746 watts x 3% warmth reduction = 22 watts of heat reduction for each 1 HP

  • 1 watt = 3.4 Btu/h

  • 22 watts x 3.4 BTU/h = 75 BTU/h for each 1 HP

Passive Cooling Rule of Thumb

For passive cooling options, these kinds of as the Pfannenberg Datawind Filterfan®, the rule of thumb is

4 CFM is essential for every single 1 HP to preserve 10°C earlier mentioned ambient in the enclosure

In other words and phrases, for a 100 HP travel, 100 CFM is needed.

This rule of thumb is derived from the adhering to equation

1 CFM = 1.82 x watts of heat decline / Δ Temp (°C)

These rule of thumb guides offer a standard guideline for deciding on a cooling system and for sizing the cooling load requirements. For more precise calculations that account for ambient temperature and humidity and other vital issues, we supply Pfannenberg Sizing Application at no demand.

By simplifying the calculation of cooling requirements, we hope that the adoption of VFD engineering will continue to expand promptly, and that end users will profit from utmost effectiveness and company lifetime.

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