UMass Medical School Fan Array

The Electronically Commutated Motor, or ECM, has infiltrated the small fan market. The technology gained ground several decades ago, mostly with small scale process applications and residential air conditions. More recently the ECM fan has made a huge impact with fan powered boxes. Currently they’re being used on fan coil units; air cooled condensers, evaporator coils, bio-safety cabinets, and a host of other small fan applications. Although limited to low pressure air systems (~ 4.0” w.c.), there have been recent improvements in the technology that suggest the ECM can do more, even central air handling systems. With this technology an air delivery systems can be optimized with incredible turn down efficiencies and flow control between central and terminal fans.

The benefits of the ECM fan versus the more traditional permanent split capacitor (PSC) induction motor is that the ECM is powered by direct current (DC) electricity with electronic commutation systems, rather than mechanical commutators and brushes. While AC current is connected to the ECM motor, it has an internal rectifier that converts AC current to DC power. The current-to-torque and frequency-to-speed relationships of an ECM are linear, and therefore extremely more efficient at part loads. This is even more apparent when you include the drive losses on three phase motors.

There is an array of ECM fans at the University of Massachusetts Medical School (UMMS) South Street facility that serve a 7,400 square foot data center. Each array consists of (12) 7.5 HP ECMs, with backwards curved fans, that can deliver 83,000 CFM at 2.5” w.c. The two arrays combined can deliver a total of 166,000 CFM, which is enough air to cool the maximum design data center heat load of 1.2 MW (SA=75F to RA=100F). The air distribution system is a plenum design that allows for a low pressure drop at maximum design flow (T.S.P < 2.0”). The 24” raised floor is maintained at a constant positive pressure of 0.05” by an array of static pressure sensors under the floor that modulate the discharge of the ECM arrays. The turndown of the ECM array is so good that perforated tiles are only added with new IS equipment, unutilized floor space is left all solid tile. Each added perforated tile delivers the design air flow. Rack mounted temperature sensors let the facility staff know if more tiles (or even grates) are needed. The supply air flow closely matches the IS equipment air flow, saving tremendous amount of fan power. What’s more, the air flow system can seamlessly grow with data center load without compromising on efficiency.

The ECM fan is directly controlled by the Building Management System (BMS); a single fan on the array can be modulated, start, stop, measure air flow, pressure drop, and power draw. The ECM array provides not only an energy efficient central fan, but provides redundancy with easy to replace multiple fans. The motors also have a longer life cycle and take up less space than traditional fans. A potential candidate for an ECM array in a large building central air handling systems could be a dedicated outdoor air system (DOAS) with the primary air distribution sized for low pressure drop, and ECM fan powered terminal units as well. A facility with such a system, combined with a robust BMS, would be capable of turning down the central air system to closely match only what the terminal units need for primary air; even if it’s just one terminal unit calling. The manufacturer of the ECM fans at UMMS; http://www.ebmpapst.us/

Questions on ECM Fans,  askRick?

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Project Snapshot: WCCC UMass Data Center | Custom Air Handling Units

This is clever and a really nice feature that can be added to any Energy Recovery Unit (ERU) or Air Handling Unit (AHU).  Just needs to be specified.
I am not sure why we didn’t think of it.  We saw this during a recent visit to Annexair.  They can now include a separate recessed control panel into a unit.  This allows an operator to access controls separate from high voltage feeds.  It’s a lot easier to maintain controls and safer for the technician.  I am sure other manufacturers can do this.  We think it’s worth asking for.  Take a look at how clean this is.

More questions on Energy Recovery Units;  askRick?

Project Highlights:

History: The Whitin Observatory is the home of the Wellesley College Astronomy Department and houses classrooms, astronomy laboratory facilities, the Astronomy Library, and faculty offices.  Built in 1900, and enlarged in 1906 and 1966, it was ready for expansion and renovation scheduled for 2009-10.

HVAC Highlights:  Piping was routed underground from the Science center so Hot Water/Chilled Water could be used for heating and cooling.  To meet ventilation code and save energy an enthalpy wheel type ERU was installed to condition all spaces.  The new unit included filters, Enthalpy Wheel, dual function Hot Water/Chilled Water coil, Direct Drive fans and an electric heater for reheat or backup.

Rigging Challenge:  Although the design supply (2,200 CFM) and exhaust (1,900 CFM ) was relatively low, the unit was still 13 ft. Long and 5 ft wide.   The unit was to be located in the corner of the basement where it would be closed in after install.   Access to the basement corner was through an opening in the floor and enlarged brick hole.  The unit was designed in 4 sections with 3 splits to be field joined by the EM Duggan crew.

Unit Controls:   The unit was designed with VAV capabilities and programmed for schedules and CO2 sensing.   The unit came equipped with damper actuators, freeze protection override on the wheel and VFDs with I/O points factory wired to a terminal strip.  The Direct Drive fans and Enthalpy Wheel were also factory wired and designed for quick connect in the field.  All other controls were provided by the ATC contractor.  The electrical and ATC contractors reconnected the loose power wire ends to the 3 motors and added their sensors and flow stations where needed.  They also conveniently located and mounted a unit control panel.  The panel provided run and speed signals to VFDs,  Enthalpy Wheel control, damper signals, and Hot Water/Chilled Water valve position.

Questions on Field Erected Air Handling Units, askRick?

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Project Snapshot: Field Erected Heat Pipe System

Konvekta Coil - Dartmouth College Burke Hall

A.  Konvekta pumped glycol energy recovery coils work anywhere in the range from 50-1000 FPM face velocity.  It’s typical for coils to be sized between 350 and 500 FPM. 

There is always a trade-off between face velocity ( air pressure drop -> fan power) and thermal efficiency.  In general, the lower the face velocity, the higher the thermal performance, and the higher the face velocity the higher the air pressure drop and hence fan power.   Designing an energy recovery system, Konvekta always takes the cost of heating (thermal energy) and the cost of electric power (fan, pump) into account and designs the system at the optimal point considering the trade-off in thermal efficiency and electric power consumed.

More questions about Pumped Glycol Coils,  askRick?

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A.  Strobic Air recommends that the Tri-Stack Fan be mounted on a 1½” wide strip of ¼” neoprene pad.  No further vibration isolation is required or recommended.

Tri-Stack fans are balanced to below 0.5 mil at the blade pass area, with measurements on the roof base as low as 0.1 mil in the vertical.   At this virtually nonexistent vibration level, at the fan frequency of 1170 RPM, the recommended vibration pad (50 durometer neoprene, 0.14” static deflection, 502 CPM average natural frequency) will have an efficiency well over 90%. 

The Tri-Stack fan mixed flow impeller has a non-stall characteristic and is perfectly stable along the entire pressure versus volume curve.  Other centrifugal type fan wheels experience a stall region under low flow, high-pressure system conditions.  During fan stall one side of the fan blade is doing more work than the other.  In this condition, the centrifugal fan vibrates violently, mandating spring vibration isolators.  Again, the Tri-Stack Impeller is perfectly stable and can smoothly operate at no flow, full pressure and it will not go into stall.

 Vibration is primarily transmitted radially from the direction of rotation.  The Tri-Stack mixed flow impeller is oriented so its radial direction is in the horizontal plane and thus transmits minimal vibration downward into the roof.  Centrifugal fan arrangements radial component are in the vertical plane, therefore a majority of the vibration is transmitted into the roof.

 We recommend that the Tri-Stack fan be mounted on neoprene pad.  Spring vibration isolators are not necessary and will detract from system stability.  In addition, flexible connections are required when using spring isolators and are widely recognized as point source failures.

More questions about High Plume Dilution Fans;  askRick?

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A.  As it stands ANSI/ASHRAE Standard 62.1-2010 is not clear on the question of Class 4 exhaust (which includes lab fume hood exhaust).  The standard reads as follows:

5.16.3.3.2 Class 3 air shall not be recirculated or transferred to any other space.

Exception:  When using any energy recover device, recirculation from leakage, carryover, or transfer from the exhaust side of the energy recovery device is permitted.  Recirculated Class 3 air shall not exceed 5% of the outdoor air intake flow. 

 5.16.3.4 Class 4 Air. Class 4 air shall not be recirculated or transferred to any other space nor recirculated within the space of origin.

Since there are no exceptions listed for Class 4 air this can be interpreted to mean that absolutely no cross airflow is allowed and would in turn not allow the use of total energy recovery devices serving laboratory fume hoods.  

Help is on the way.  In February Ashrae published Proposed Addendum k to Standard 62.1-2010.  It is now in final review and comment stages.  This proposed addendum adds an exception to the recirculation limits on Class 4 exhaust air streams from laboratory hoods which would allow use of heat wheel energy recovery in some cases.  The exception defines several criteria which the airstream must meet before such heat recovery can be used, and the heat recovery system must limit recirculation airflow to less than 0.5% of the outdoor air intake flow.

Addendum k to 62.1-2010 -  proposed to revise Section 5.16.3.4 as follows:

Section 5.16.3.4  Class 4 Air. Class 4 air shall not be recirculated or transferred to any space nor recirculated within the space of origin.

Exception: When using any energy recovery device, recirculation from leakage, carryover, or transfer from the exhaust side of the energy recovery device is permitted subject to the following restrictions:

 a. Laboratory exhaust from facilities where the use of chemicals is related to testing, analysis, teaching, research or developmental activities and where chemicals are used or synthesized on a nonproduction basis, rather than in a manufacturing process, provided that: 

1.  The laboratory is classified as BSL 2 or lower,
2.  The exhaust air from a BSL 3 laboratory has been HEPA filtered prior to entry into the heat recovery system,
3.  The laboratory does not handle explosive or reactive chemicals that could accumulate or react on or within the heat recovery system, and
4.  The mass balance calculations specified in the IAQP shall be used with the emissions to be handled by the exhaust system to ensure that resulting concentrations in the space are below acceptable limits, such as those specified in Appendix B.

b. Recirculated Class 4 air shall not exceed 0.5% of the outdoor air intake flow.

Further questions on Energy Recovery Wheels;  askRick?

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Ask Rick: Energy Recovery Wheels on Laboratory Fume Hood Exhaust?
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Project Highlights:  

Existing Conditions:  Football is a proud tradition in East Boston and funding was raised to replace original and antiquated HVAC equipment in the Stadium.  6800 CFM was going to be required to meet ventilation rates for the offices, locker rooms, showers and other spaces.   A boiler upgrade was also part of the project.  The mechanical space had a small man entry and an awkward shape.  A floor cut of the concrete was agreed on and the engineer tried to select a Packaged Energy Recovery Unit that would fit.  The floor access could not be cut large enough to rig a packaged unit and a custom field erect unit was not in the budget. 

The Solution:  Engineered Systems, Inc. (ESI) selected a supply and exhaust fan to move the required air.   David Goodman from DAC Sales sized and selected a passive Heat Pipe Energy Recovery Module and 5 Hot Water reheat coils, the largest to be located after the Heat Pipe in the mechanical space.  The Heat Pipe selected was 120”L X 40”H – 6 Row – 12 FPI.   The Heat Pipe, Hot Water Coil and filters were connected to the fans with simple ducting connections.  All these parts were chain fall lifted through the new access hole and field assembled according to the plans. 

The Results:  The Heat Pipe greatly reduced the new boiler sizing and energy consumption.   283,000Btu’s/hr. were saved at design conditions.  A by-pass damper was also included to provide frost protection on very cold days.

More questions on Heat Pipe systems;  askRick?

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This is a quick overview of how a Heat Pipe works in an HVAC system.   More specific information can be found in free webinars from Heat Pipe Technology.

Further questions on Heat Pipes feel free to askRick?

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• A Desaturation Cooling Coil (Desat Coil) really functions like two separate coils.  It combines the aspects of a cooling coil and a reheat coil to cool, dehumidify and reheat the air.  The Desat Coil includes an additional coil row in the leaving air side of the coil, called an “integral re-heat loop.”   The return water passes through the last row providing a couple of degrees of reheat (typically 2-3 degrees).  Pretty simple,  but effective. 

• The elevated discharge temperature lowers the relative humidity from 100% to 90%, in effect desaturating the air as it leaves the cooling coil.

We routinely use desat coils in laboratory or other critical applications in tandem with heat recovery options. We design these applications with the supply fan in a blow-thru position upstream of the energy recovery device (wheel or heat pipe) to minimize the potential of leakage through the device.   In this arrangement, without the supply fan motor heat added downstream of the cooling coil, the desat coil provides an easy way to sensibly raise the leaving air temperature off the cooling coil (usually by 1.5° to 3.0°F).

Read more on the Aerofin Desaturation Coil
Related Blog Post: Ask Rick: When do you use a Desaturation Coil?

More questions about Desat Coils;  askRick?

A.  Great Question.  We use pumped glycol energy recovery systems all the time here in the United States.  Up until recently we have almost exclusively used Propylene Glycol.  Ethylene Glycol had not even been a choice. 

The biggest reason for this is that Ethylene Glycol is toxic.  If you drink a couple of ounces, you die.  During Prohibition this actually happened.  People drank just about anything they could distill, including ethyl alcohol.  People died,  and people remembered that. 

What the heck!  The main ingredient in the vast majority of automotive antifreeze on the market today is ethylene glycol.   It’s also in most of the wind shield washer fluids.  We’re either dripping it on our garage floor or spraying it all over our windshields,  so why not use ethylene glycol in our pumped glycol energy recovery systems?

Benefits of Ethylene Glycol Solutions:

• higher heat transfer coefficient
• better freeze point depression
• higher surface tension, less leaks
• about 10% more efficient than Propylene Glycol in pumped systems

 Because Ethylene Glycol is toxic it is more closely regulated than Propylene Glycol.  Still you have to spill hundreds of gallons before reporting.   The Environmental Protection Agency has a reportable quantity (RQ) for spills of 5,000 pounds (539 gal.).  That’s a huge spill. 

Ironically, even though ethylene glycol is listed due to its toxicity, the environmental harm caused by the product contaminating an ecological area is less than propylene glycol because its decomposition rate is faster by half.  Thereby having a far lower Biological Oxygen Demand (BOD) than propylene glycol.  So Ethylene Glycol is actually greener.

Finally,  it’s worthwhile to point out that our friends in Europe and Canada only use Ethylene Glycol in their energy run around loops.  Propylene Glycol is not considered as an option.

At DAC Sales,  we are using Ethylene Glycol in nearly all of the systems that we design with Konvekta here in the United States.  Looks like it’s time for a change.

More questions on pumped glycol systems;  askRick?

Great information from Konvekta:  Ethylene vs. Propylene Glycol
Dow Chemical Paper: Ethylene vs. Propylene Glycol

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