City of Chicago Ventilation rate tabl…

City of Chicago Ventilation rate table

Attached below is ventilation rate table for City of Chicago. It provides ventilation rate for most normal occupancy in a building within the city. This would be required for HVAC system design for any projects within the city. It is adopted from the Municipal code section of City of Chicago.

City of Chicago Ventilation Requirements

Smoke Detectors on Fan Systems r…

Smoke Detectors on Fan Systems requirement IMC and NFPA 90A

IMC 2009 requires smoke detectors on fan systems with capacity greater than 2,000 CFM on return duct or plenum upstream of any filters, exhaust air connections, outdoor air connections, or decontamination equipment and appliances. There are several exceptions. See below.

NFPA 90A requires smoke detectors Downstream of the air filters and ahead of any branch connections in air supply systems having a capacity greater than 944 L/sec (2000 ft3/min)

See below for all exceptions:

From IMC 2009 “606.2 Where required. Smoke detectors shall be installed where indicated in Sections 606.2.1 through 606.2.3. 

Exception: Smoke detectors shall not be required where air distribution systems are incapable of spreading smoke beyond the enclosing walls, floors and ceilings of the room or space in which the smoke is generated.

606.2.1 Return air systems. Smoke detectors shall be installed in return air systems with a design capacity greater than 2,000 cfm (0.9 m3/s), in the return air duct or plenum upstream of any filters, exhaust air connections, outdoor air connections, or decontamination equipment and appliances.

Exception: Smoke detectors are not required in the return air system where all portions of the building served by the air distribution system are protected by area smoke detectors connected to a fire alarm system in accordance with the International Fire Code. The area smoke detection system shall comply with Section 606.4.
606.2.2 Common supply and return air systems. Where multiple air-handling systems share common supply or return air ducts or plenums with a combined design capacity greater than 2,000 cfm (0.9 m3/s), the return air system shall be provided with smoke detectors in accordance with Section 606.2.1. Exception: Individual smoke detectors shall not be required for each fan-powered terminal unit, provided that such units do not have an individual design capacity greater than 2,000 cfm (0.9 m3/s) and will be shut down by activation of one of the following:
1. Smoke detectors required by Sections 606.2.1 and 606.2.3.
2. An approved area smoke detector system located in the return air plenum serving such units.
3. An area smoke detector system as prescribed in the exception to Section 606.2.1. In all cases, the smoke detectors shall comply with Sections 606.4 and 606.4.1.
606.2.3 Return air risers. Where return air risers serve two or more stories and serve any portion of a return air system having a design capacity greater than 15,000 cfm (7.1 m3/s), smoke detectors shall be installed at each story. Such smoke detectors shall be located upstream of the connection between the return air riser and any air ducts or plenums.
From NFPA 90A: 6.4.2.1: Smoke detectors listed for use in air distribution systems shall be located as follows:
  • Downstream of the air filters and ahead of any branch connections in air supply systems having a capacity greater than 944 L/sec (2000 ft3/min)
The purpose of these smoke detectors is to shut down the air handler (fan) of the single unit it is serving in the event of a fire or smoke from the motor, filter, belts, and so on, of that unit. The fire load from those items is small and will likely burn out long before first responders can arrive. In addition, the amount of smoke generated will likely not migrate out of the system once the fan is shut down. Hence, there is no requirement to sound an evacuation alarm because an evacuation is more likely to cause problems than the small amount of smoke.
  • At each story prior to the connection to a common return and prior to any recirculation or fresh air inlet connection in air return systems having a capacity greater than 7080 L/sec (15,000 ft3/min) and serving more than one story

6.4.2.2 Return system smoke detectors shall not be required where the entire space served by the air distribution system is protected by a system of area smoke detectors.

There are two purposes for smoke detectors on returns. The first is to shut down the air handler (fan) of the single unit it is serving in the event of a fire or smoke from the motor, filter, belts, and so on, of that unit and to close the smoke dampers required by 4.3.9.2 to contain smoke from a fire in the unit. The second is to provide shutdown where smoke might migrate from other floors through a common return prior to shutdown by the supply side detector. The committee considers area detection, and therefore a building alarm, sufficient for occupant safety so that the return side detector is not required where there is area detection.


6.4.2.3 Smoke detectors shall not be required for fan units whose sole function is to remove air from the inside of the building to the outside of the building.

There are two purposes for smoke detectors on returns. The first is to shut down the air handler (fan) of the single unit it is serving in the event of a fire or smoke from the motor, filter, belts, and so on, of that unit and to close the smoke dampers required by 4.3.9.2 to contain smoke from a fire in the unit. The second is to provide shutdown where smoke might migrate from other floors through a common return prior to shutdown by the supply side detector. The committee considers area detection, and therefore a building alarm, sufficient for occupant safety so that the return side detector is not required where there is area detection.

Commissioning Variable Primary Chill…

Commissioning Variable Primary Chiller Plant

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One of the most significant ASHRAE Standard 90.1-2010 updates was the requirement for HVAC commissioning on most projects greater than 50,000 sq ft. The U.S. Green Building Council’s LEED Energy and Atmosphere perquisite 1 (EAp1) requires fundamental commissioning of building energy systems.

Most chiller plant and fan system commissioning can produce energy savings that can pay off in six months to two years and create value for the owner for the entire life of the equipment. The payback is even quicker for facilities that operate 24×7, like hospitals, data centers, 911 centers, telecom equipment buildings, and others.

Our engineering firm validated the significance of commissioning during an HVAC commissioning project at an existing telecom equipment building in Illinois. The owner didn’t have a commissioning plan and invited the design team to perform acceptance commissioning (carry out functional performance tests on HVAC systems). The building is more than 20 years old with gross floor area of approx. 350,000 sq ft. It has three floors including basement. Half of the building houses telecom equipment like switches, transport equipment, a rectifier plant, and a battery plant, which require cooling for 8,760 hours in a year. This is a low heat density environment, and a traditional air handling unit (AHU) with distribution ductwork is able to cool the equipment. The other half of the building consists of offices for support staff. Most of the offices are vacant and currently served by an existing system independent of the system serving telecom equipment.

The need for commissioning

In the HVAC system upgrade project, for which construction was completed a year ago, a new chiller plant and air handlers were added to the building. The HVAC equipment was dedicated for cooling telecom equipment. One year after the substantial completion and start-up, the design team was called to commission the project and solve the following maintenance issues:

  • The chiller would shut down on low flow several times a week and would generate an alarm.
  • The chiller plant was designed to operate with one pump (the second pump was designed as a redundant pump), but the maintenance team was operating both pumps together to avoid tripping of the chiller on low flow.
  • When the pump’s variable frequency drive (VFD) was manually put on bypass mode, it would overload and the motor would become hot. Eventually, the motor would trip on high temperature.
  • Maintenance was also experiencing high humidity in the telecom equipment space.

The new cooling equipment consists of a central chiller plant and AHUs. The chiller plant consists of one 90-ton packaged air cooled chiller, two chilled water pumps (primary and redundant), two chilled water cooling coils (one at each air handler), and pressure-independent valves at each cooling coil and bypass. The chiller plant is designed as variable primary system (see Figure 1).

AHU-1-1 and AHU-2-1 have a chilled water cooling coil and 100% outside air economizer. The outside air economizer provides free cooling whenever ambient temperature and humidity allow. AHU-1-1 is located on the first floor and serves the basement and first floor. AHU-2-1 is located on the second floor and serves only the second floor. The air handlers are equipped with high-efficiency filters.

The chiller plant and air handlers were oversized for future capacity. The building owner was expecting to double the load in the building over the next five years and wanted the engineer to design the system for ultimate future capacity. The HVAC system upgrade was a large capital expense, and the owner wanted it to serve current as well as future needs.

Commissioning, troubleshooting

The design team carefully reviewed, measured, and tested data including air- and water-side tests and balance reports. The team also reviewed the BAS logs and trends, and visited the site to find following operational issues:

  • The chiller differential pressure (DP) switch that monitors the minimum flow through the chiller was set for the full design flow (189 gpm), as opposed to minimum flow as specified by the manufacturer (100 gpm).
  • Chilled water pumps were controlled to maintain 18 psi across the most remote AHU coil pressure-independent valve, as opposed to 5 psi required by design. This was unnecessarily pressurizing the system and wasting pump energy.
  • The flowmeter controlling the bypass valve was not calibrated and was calling for the bypass valve to open 100% of the time. The flowmeter was controlled to maintain full design flow through the system at all times.
  • The chiller was seeing delta T of 3 F. The chiller plant was suffering from low delta T syndrome.
  • During bypass mode, the pump would ride so low on the pump curve that it would overload and trip the motor.
  • The air handler supply air temperature was in the range of 64 to 67 F. This gave very little opportunity for de-humidification, resulting in high space humidity (62% to 65% relative humidity, RH).

To resolve these issues and save a substantial amount of energy, the following steps were taken in a sequential manner while carefully observing system performance over two days:

  1. The chiller DP switch was replaced. DP on the switch was set to flow corresponding to the minimum flow-through chiller as specified by the manufacturer (100 gpm).
  2. Chiller water pumps were now controlled to maintain 5 psi across the most remote AHU coil pressure-independent valve as required by the design.
  3. The flowmeter was calibrated and the bypass valve was set to maintain 100 gpm through the chiller.
  4. With these changes, the engineering team was able to run the chiller plant with only one pump operating. As a bonus, the pump didn’t trip the VFD, which was put on bypass because it would never ride that low on the pump curve (see Figure 2).
  5. The air handler supply fans were ramped down to 60% and 65% of full speed using a VFD. This dropped the supply air temperature to 58 to 59 F and space humidity to 54% to 55% RH.

Energy savings

The above measures not only solved all operational issues, but also created significant energy savings for the owner. The energy savings from pumps and fans were calculated to be $8,163 per year. This also represents the lost energy savings potential because commissioning was delayed by almost a year. The total cost for commissioning was $5,800. This results in a simple payback of 8.5 months. If these issues were not addressed, the owner would have spent an additional $163,263 over the life of equipment (20 years), without considering any increases in utility costs and interest rates.

Commissioning is one of the most complex and important parts of building construction. ASHRAE 90.1-2010 has mandated it on all HVAC systems in commercial buildings larger than 50,000 sq ft, and it is also a prerequisite in LEED v3. It is widely recognized and proven that commissioning pays back in less than two years—and often sooner.

The owner was delighted with the results of the HVAC commissioning at the end of the project. The building owner has a policy of actively pursuing energy savings projects that pay back in less than two years. It was also a big boost for the commissioning team, which also served as the design team in this case.

CONTAINMENT STRATEGIES COMPARISON IN …

CONTAINMENT STRATEGIES COMPARISON IN DATA CENTERS

This article compares ten different containment strategies for data centers. Containment strategies discussed includes hot aisle containment, cold aisle containment, end aisle containment for both hot and cold aisles, hot and cold aisle containment, cabinet chimney containment, and other variation of containment strategies.  The model uses cabinet heat load of 3.8 kW to 34.5 kW. It concludes that hot aisle and cold aisle containment together offers the best performance both in terms of minimum inlet temperature and energy usage followed by cold aisle containment. It appears cold aisle containment provides the best value for money in these kinds of data modeled data centers.  The research for this article was done by Affiliated Engineers (http://www.aeieng.com/). The article here is shared here only for education and non profit purposes.

ThermalEfficiencyResultsinGreenerDataCenterContainmentPart-1

ThermalEfficiencyResultsinGreenerDataCenterContainmentPart-2