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CASE STUDIES

VAV SYSTEM MODIFICATIONS ON AHU & TERMINAL EQUIPMENT

Overview

The VAV system services a large commercial office building that has a high usage density and prioritizes occupant comfort.  Therefore, the building has high energy usage.

The Goal

Building owners were looking for ways to reduce operating costs.  With intimate knowledge of mechanical systems, modern energy reduction modifications were applied to the central equipment (AHU) and terminal units (VAVs).

The Solution

An investigation of the AHU revealed the need to reconfigure the method in which it modulates air volume.  The AHU's fan speed was modulated by a constant volume centrifugal fan that used electronically controlled inlet vanes.  The vanes would close to reduce air volume and modulate open increase air volume.  Replacing this with an axial fan wall, VFD, and removing the vanes achieved variable air volume control while at the same time reducing energy consumption. 

With regards to the VAVs, the original series fan powered boxes were replaced with parallel boxes, thereby reducing the static pressure.  A parallel configuration reduces the electrical load by slowing down the AHU supply fan since a series terminal unit fan acts as a restriction that the blower needs to overcome.  Because the terminal fan needs to run when the supply fan runs, space reheat during unoccupied periods requires operation of the AHU blower.  A parallel VAV box can reheat without the extra energy burden.

Conclusion

As technology updates, mechanical systems should be modernized with more energy efficient strategies.  Modifying existing equipment may be the easiest way to boost energy efficiency in your building.

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GEOTHERMAL HEAT EXCHANGER FLOW TRACKING TO MATCH DHW DEMAND

Overview

Because hotels use high volumes of domestic hot water, a geothermal system can yield high energy savings. In this case, geothermal hot water at 110F is used to preheat the domestic cold water before entering a set of boilers.  The condensing gas boilers then boost the water temperature and store 160F water.  However, instead of reducing the operating cost, a significant increase was seen in the energy bill.

The Goal

To decrease geothermal cost below that of natural gas the thermal efficiency of the heat exchanger needed to be maximized by maximizing the temperature differential.

The Solution

Initial analysis on the heat exchanger design proved that it was sized appropriately to make it more cost effective than natural gas.  The temperature differential was large enough to extract more energy per cost than that of natural gas.

Thus, the inherent problem was discovered in the geothermal VFD pump design due to the nature of the building's instantaneous hot water demand.  The pump introduces geothermal water on one side of the heat exchanger when there is a call to preheat cold water on the demand-side of the heat exchanger, as indicated by the adjustable flow switch.  However, the majority of the building's instantaneous demand occurred briefly or at low flow rates.  The pump's operational parameters did not meet the demand, thus the heat exchanger did not operate at its maximum thermal efficiency.

To maximize the thermal efficiency, flow meters on the geothermal and demand-side were installed.  As the demand-side flow is monitored the geothermal flowmeter indicates the pump's speed.  Matching the volumetric flowrate on both sides of the heat exchanger ensures maximum efficiency while minimizing water usage.

Conclusion

Although a heat exchanger may be properly designed, an improperly operated heat exchanger will cost more to operate than conventional utilities, resulting in an impractical use of a renewable energy source.

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CRITICAL ENVIRONMENT CONTROL USING FAN COILS, HUMIDIFIER, ERV, & GUI

Overview

Hot Yoga Studios require higher-than-normal space conditions through the duration of classes.

The Goal

Critical control elements include maintaining a high temperature setpoint, moisture, and ventilation control while at the same time trimming energy usage.  In addition, user adjustability of a parameter is crucial for modifying conditions in real-time.

The Solution

To achieve the desired space conditions the mechanical system was designed with a hydronic hot water system coupled with fan coil wall units, a space humidifier, and an energy recovery ventilator.  During occupied periods, the space reaches up to 110F, up to 60% relative humidity, and dilute metabolic pollutants via ventilation.  With an energy dense environment, the ERV recaptures the exhausted sensible and latent energy for reuse in the space.  When the space is vacated, it is purged and cooled to prevent biological growth and reduce lingering metabolic pollutants (carbon dioxide and odor).

User adjustability is accomplished using any web browser.  Therefore, with a simple GUI layout, the operator can access and adjust setpoints, schedule classes, and monitor performance using statuses and data trends, all by means of a smartphone, tablet, and/or PC.

Conclusion

Controlling critical environments can be challenging.  Difficulties often arise in control because of the limitations of the mechanical system.  To meet the environmental criteria, Airtek Design Group will ensure careful design and successful implementation.

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DATA CENTR COOLING SYSTEM REDESIGNED WITH IN-ROW COOLERS & CONTAINMENT

Overview

The data centers for state buildings need to be secure, reliable, and protected.  In transitioning from a traditionally purely paper file system to a digital one, as well as increase in software performance requirements, the necessary cooling capacity per area for the data load exceeded the available floor space.

The Goal

Because the data load expanded beyond the limits of the existing data center cooling system cooling capacity, a complete redesign was necessary to meet the data centers cooling capacity requirements.

The Solution

The original system had underfloor air distribution (UFAD) with fan coils.  After a cooling load analysis, a water cooled containment system was sized, designed, and installed that could achieve a higher cooling density at a smaller footprint.  In addition, added security measures were implemented and the APC power system was integrated into the existing DDC. 

Conclusion

Careful system analysis and consideration of existing options can yield cost-effective solutions that can still fit within your particular constraints.

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