Lawrence Berkeley National Laboratory
Improving Ventilation and Saving Energy
Relocatable classrooms (more commonly known as portable or mobile classrooms) are in wide use in California schools. They allow school districts to quickly and economically adapt and expand their schools’ infrastructure to accommodate the ever-changing student populations. In 2000 there were an estimated 80,000 relocatable classrooms (RCs) in use within California schools with a projected increase of 4,000 new units per year (CARB/CDHS 2003, EdSource 1998, Sarich 2001). A joint study conducted by the California Air Resources Board and the California Department of Health Services (CARB/CDHS 2003) from 2000-2002, focusing on the indoor environments of schools, found that ventilation rates and indoor environmental comfort in RCs were often below current standards and in need of improvement.
To this end the Improving Ventilation and Saving Energy (IVSE) study aims to develop, evaluate, and demonstrate a practical Heating, Ventilation and Air Conditioning (HVAC) system for use in RCs in schools. The IVSE study is a collaborative effort between Lawrence Berkeley National Laboratory, the Bard Manufacturing Company, a leading manufacturer of wall mounted HVAC systems for RCs, and Geary Pacific Supply Corporation, the West Coast distributor of Bard HVAC equipment. The goals of the HVAC system under development and testing are to provide consistent ventilation to RCs while simultaneously reducing overall energy consumption and HVAC related noise.
Inconsistent and low ventilation rates lead to a build up of airborne pollutants such as volatile organic compounds (VOCs) that can be harmful to human health. Adverse affects of poor ventilation can include sick building syndrome and other respiratory illnesses (Seppanen et al, 1999, Wargocki et al. 2002, Erdmann et al. 2002). The American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) Standard 62.1-2004 (ASHRAE, 2004), as well as the State of California Building Standards and Occupational Safety and Health Codes require a minimum ventilation rate of 15cubic feet per minute (CFM) per person (CA Title 24, 2001; CA CCR Title 8, 1995) in classrooms. Current RC ventilation rates often do not meet these requirements and thus VOCs and other pollutant concentrations in classrooms can frequently be found at elevated levels. As it is difficult and expensive to measure levels of many other indoor air pollutants directly and in real time, indoor carbon dioxide (CO2) concentrations are often used as an indicator for indoor air quality. High levels of CO2 in occupied rooms imply poor ventilation and increased pollutant concentrations while lower levels of CO2 correspond to increased outdoor air supplied to the classroom and decreased levels of indoor pollutants.
A contributing factor to low ventilation rates, the high levels of CO2 and other compounds in RCs is the manner in which HVAC systems are currently operated. The CARB/CDHS (CARB/CDHS 2003) study found that about 60% of teachers turned off their RC ventilation system during class time due to the high level of noise generated by the system thereby reducing the amount of classroom ventilation. Because of this the advanced HVAC system is being designed to significantly reduce operational noise levels when compared to currently available HVAC systems. This will allow the new HVAC system to continuously operate and provide ventilation to the RC without producing distracting levels of noise.
In addition to reducing noise, the IVSE study hopes to show that the new HVAC system uses at least 30% less energy than the 10 Seasonal Energy Efficiency Ratio (SEER) systems within varying climate conditions in California, while at the same time providing sufficient outside air ventilation to RCs so that CO2 concentrations can be maintained below 1000 ppm.
The current IVSE HVAC system under development is being designed to be interchangeable with systems that are currently in use. The reason for this is that the ability of the new system to work with existing RC HVAC configurations will speed up the market transition from current HVAC systems to new advanced HVAC systems. In addition, it will also reduce the cost of replacement and the financial burden placed on school districts that choose to replace their current RCs HVAC systems. In order to maximize the speed of the transition throughout the HVAC industry, a public specification for of the advanced HVAC system will be available after the analysis of the field study data is completed so that other manufacturers of HVAC systems can make similar improvements.
IVSE Study Goals
Energy Efficiency Goal
To demonstrate that the energy consumption of the advanced HVAC system is at least 30% less than current 10 SEER systems and therefore a 10% improvement compared to 12 SEER systems in both laboratory and field settings in California’s varying climate conditions.
Noise Reduction Goal
To confirm the operational noise level of the advanced HVAC is less than or equal to 45 dB(A) in classrooms.
Ventilation System Improvement Goal
To show that the new advanced HVAC system is physically interchangeable with current HVAC models in use on RCs while providing the following:
Continuous outside air ventilation in amounts that meet the current California Energy and Occupational Codes and ASHRAE 62 Standard
Real time signals to the ventilation unit that will constantly and continuously ventilate the classroom when it is occupied regardless of temperature
Indoor CO2 concentration below 1000ppm at all times
Air velocities and temperatures that lead to acceptable thermal comfort base upon the ASHRAE 55 Standard
Before field studies of the advanced HVAC began, the system was evaluated onsite at Lawrence Berkeley National Laboratory using a simulated classroom setting. Lab evaluation occurred during the summer and fall of 2004. A single RC unit was installed at LBNL for testing. The classroom was outfitted with the advanced HVAC system as well as a standard 10 SEER HVAC system for comparison. Sensors were installed to monitor indoor air quality, temperature and energy use. 30 light bulbs were used to simulate the thermal presence of students during the day and CO2 was released at a controlled rate to simulate the occupant’s respiration.
While final analysis of the data collected is underway, preliminary results look favorable. The advance HVAC system was able to be directly bolted onto the RC without major modification and used about 56% of the energy of the control 10 SEER HVAC system. In addition, the operational noise produced by the advanced HVAC system was lower than the goal of 45 dB(A). The worst-case integrated (A-weighted) noise level recorded for the advanced HVAC was 43 dB(A) when the heat pump was operating on high, while integrated (A-weighted) noise levels were below 32 dB(A) when only the fan was operated (see octave band sound pressure level (SPL) graphs available at Before field studies of the advanced HVAC began, the system was evaluated onsite at Lawrence Berkeley National Laboratory using a simulated classroom setting. Lab evaluation occurred during the summer and fall of 2004. A single RC unit was installed at LBNL for testing. The classroom was outfitted with the advanced HVAC system as well as a standard 10 SEER HVAC system for comparison. Sensors were installed to monitor indoor air quality, temperature and energy use. 30 light bulbs were used to simulate the thermal presence of students during the day and CO2 was released at a controlled rate to simulate the occupant’s respiration.
While final analysis of the data collected is underway, preliminary results look favorable. The advance HVAC system was able to be directly bolted onto the RC without major modification and used about 56% of the energy of the control 10 SEER HVAC system. In addition, the operational noise produced by the advanced HVAC system was lower than the goal of 45 dB(A). The worst-case integrated (A-weighted) noise level recorded for the advanced HVAC was 43 dB(A) when the heat pump was operating on high, while integrated (A-weighted) noise levels were below 32 dB(A) when only the fan was operated (see octave band sound pressure level (SPL) graphs available at http://eetd.lbl.gov/IEP/IVSE/lab.html).
In addition to the meeting and exceeding the energy savings and noise level reduction goals, the ventilation and thermal conditioning units were successfully decoupled allowing for ventilation at anytime regardless of the indoor temperature. This is important because it allows for ventilation independently of heating or cooling the classroom. During the lab studies, it was also established that the advanced HVAC system could provide adequate thermal comfort while meeting all of the mentioned goals.
IVSE FIELD STUDY
Currently all three goals of the IVSE study have been quantitatively tested in the field. The field study involved a total of 16 RCs in two school districts in California over the course of 2005. Ten of the classrooms were intervention classroom equipped with the advanced HVAC system and 6 out of the 10 intervention classroom were matched to control classrooms that have traditional heating, cooling and ventilation systems. Matching wa based on location, classroom size, and manufacture, grade level and classroom age to help eliminate the influence of these variables in the study.
The final report summarizing the field study data and results is due to be completed in mid 2006.
Instruments to measure a variety of indoor air quality and energy-related variables were installed in all of the study classrooms. The data collected with these instruments will be used to assess how well the advanced HVAC system meets the IVSE study goals. Some of these parameters, including indoor and outdoor air temperature, relative humidity, carbon dioxide concentrations and power use, were collected in real time, while ventilation rates, particle concentrations and size, VOC, ozone and aldehyde concentrations, sound levels, and thermal comfort measurements were collected once a season during onsite visits. Also aggregate attendance data was collected for the study classrooms through onsite visits.
Real time data was collected using the LonWorks® network protocol and an i.Lon® e2 Internet Server developed by the Echelon Corporation. LonWorks enabled sensors used in the study include the PureChoice Nose Monitor™ and Continental Control Systems WattNode® Plus. All sensors were connected to a central iLon network server that acted as a data logger and provided communication to the data servers.
References are available at http://eetd.lbl.gov/IEP/IVSE/references.html
Study made possible with funding from:
the US Department of Energy Building Technologies Program
the California Energy Commission Public Interest Energy Research
and with the cooperation of:
Mobile Modular Manufacturing, Pure Choice, Echelon, Continental Control Systems, Bard Manufacturing Company and Geary Pacific Supply Corporation
This article is reprinted with permission from Michael G. Apte, PhD, Lawrence Berkeley National Laboratory. For more information, visit