Two years ago Rick McGinley and I were contacted by Rudolf Zaengerle from Konvekta. Konvekta had done research and had singled out DAC Sales as the firm to represent them in New England.
Rick and I were not convinced that Pumped Glycol Run Around loops were viable. They had always been our least favorite means of air to air energy recovery. Traditional Glycol Energy Recovery had efficiencies near 45% in design; and 40% after pumping costs were included. That’s on paper. When they got installed and were not maintained we saw even worse results. Needless to say, not our first choice in energy recovery.
We agreed to meet with Rudolf at the Boston Airport Hilton (we made him pay for lunch). We let him know right up front that we were not big fans of Pumped Glycol Loops. We needed to be sold.
Konvekta specializes in pumped glycol energy recovery systems. That’s all they do.
They are based in Switzerland and have been in business for over 60 years, doing only pumped glycol energy recovery systems.
Last year their sales were over $60 million.
Konvekta supplies the entire package. They make their own coils, pump packages and controls.
The reason they are so successful is they are able to achieve 65-75% effectiveness with glycol loop systems and they guarantee the savings. That’s right, they guarantee the savings.
The Konvekta system is the only pumped glycol energy recovery system that will meet the new minimum efficiencies in the revised ASHRAE code.
We have represented Konvekta for two years. We have systems being installed at; Dartmouth College, Mass State Dept. of Public Health, Hudson Valley Community College and VA Medical Center Jamaica Plain. Contact Us for more information on Konvekta.
Q. I have read about Konvekta systems. They are a Swiss company. Do they manufacture any parts of their system in the US?
A. Most components are made in the USA; in particular, the Hydronic Module and its components (pumps, motors, valves, expansion tank, etc.) are made or are purchased from suppliers in the USA.
The coils are still manufactured in Switzerland. They are a shorter lead item and are more cost effective to build in the main plant.
Q: In what applications do you recommend using a desat coil?
A: In general, a desaturation coil (desat coil) will help in any application where the cooling coil is the last component in an air handling unit. The desat coil is one of several options which can provide the necessary minimal reheat so supply air doesn’t leave the unit saturated.
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 2.0°F).
Another option is to use a Wrap Around Heat Pipe. This setup provides both the reheat (5° to 15°F) and also the same amount of pre-cool upstream of the cooling coil. The Wrap Around Heat Pipe option has a higher first cost than the desat coil but provides a significantly lower life cycle cost.
Mass General Hospital CNY149 is an extremely large energy recovery system. The system includes Air Enterprises Custom Air Handling Units, Thermotech Energy Recovery Wheels and Strobic Air High Plume Dilution Fans (Tri-Stack Fans). The system was designed to replace individual fan sets that served separate hoods in all lab spaces. Massive duct sections were provided to allow for combining all exhausts. It also served general lab exhaust.
Energy Recovery Device Selection: Selecting the right energy recovery device for the application was a challenge. Energy Recovery Wheels were of course the desired choice. They are much more efficient and transfer both sensible and latent energy. They save both heating and cooling energy costs. The Energy Recovery Wheel Savings Analysis showed an expected annual savings of $767,253 ($2.4 per CFM).
Because some of the exhaust air was from fume hoods the building owner was concerned about cross contamination. In order to verify that energy recovery wheels could be used, the hospital requested a carryover assessment study. The study assumed the worst case spill for the facility with a variety of chemicals. The theoretical carry over amounts were compared with NIOSH Threshold Limit Values (TLV). In all cases carryover amounts were significantly below the NIOSH TLV. Wheels were also tested after installation with SF6 gas.
There are 4 energy recovery wheels used on this project. Each handles 80,000 CFM and is over 18 feet in diameter. At the time of install they were the largest wheels used in North America. The specification included the following: “The structural frame and casing shall be designed and manufactured so as to allow a maximum rotor deflection of 1/32 inch, as measured at the outer radius, during maximum rated airflow condition.” The installed wheels meet the required deflection specification.
Therma-Fuser diffusers are ceiling diffusers with built in room thermostats allowing individuals to select their comfort setting (temperature). We have worked with Acutherm for over 20 years and have over 25,000 Therma-Fusers installed in New England.
The ST-HC is their newest design. Check out how it operates.
A: You should use a freezestat to protect your water coils from freezing. Rooftop units with water coils should always have freezestats, even if using a water/glycol mixture.
Typically the heating coil would be upstream of the cooling coil. Usually the freezestat is attached on the leaving side of the heating coil. The freezestat won’t trip when cold air hits the Hot Water coil unless the coil isn’t generating enough heat to maintain Leaving Air Temperature (LAT) above the freezestat setpoint.
Typically freezestats are made of 1/8”OD flexible copper tubing which is filled with a temperature sensitive gas vapor (as temperature drops, gas vapor pressure drops). The tubing is connected to a bellows cup and a control box. There is usually a selectable temperature set point on the control box (35F is typical). The freezestat will “trip” if any section of the temperature sensor element drops below the setpoint. The sensor element can be various lengths, often up to 20ft long,, and will trip if any 12” to 18” length goes below the setpoint.
When a freezestat trips, the main contact opens and a button pops out on the control box. An auxiliary contact closes at the same time. Freezestat trips are usually hard-wired into the air-handling unit controls to stop the unit fans and open the Hot Water valve to full open or some minimum % open. Freezestats are designed to be reset manually by someone physically pushing the button back in on the control box.
Project Highlights: Project includes six custom all aluminum air handling units mounted on a single common plenum roof curb. All units are under a single roof to form one large AHU from the exterior. Dual service corridors provide service access to all six AHUs. The corridors also provide a location for all piping, controls, and electrical services including VFDs.
Challenge: Limited access to duct risers required a creative solution to provide 240,000 CFM to the new hospital project. Budget constraints did not allow the construction of a mechanical penthouse.
Solution: A common roof curb was segmented into supply and return plenums to direct the air into two duct risers located at each end of the unit. Sound attenuators were incorporated into the plenums in order to reduce transmitted noise. Air Enterprise constructed the six AHUs and service corridors in their factory and shipped the entire unit in 13 sections. Outside air and exhaust air had to be directed to the six units via a field constructed upper roof plenum. The roof plenum panels were provided by Air Enterprise. The upper roof plenum utilized a similar construction method to Air Enterprise’s SiteBilt system. The upper plenum required field installation due to the shipping height limitations. The 13 sections were set on the curb and the installing contractor field installed the panels that made up the upper plenum. The entire roof was then sealed with a field installed membrane roof system.
Q. Is it ok to turn an energy recovery wheel off for economizer purposes?
A. No, we do not recommend that. If an energy recovery wheel is stopped it’s flutes can clog if filters are not maintained properly. The wheel is self cleaning as it rotates through opposite air streams. It needs to run at all times.
We recommend and provide Variable Frequency Drives (VFD) on the wheel for both frost control and economizer. For economizer slow the wheel down till it’s barely moving. Energy transfer is lost and the wheel will stay clean.