Dictionary of Energy

Active Hot Water Solar Systems


Active solar hot water systems are available with air, liquid or liquid vapor collector fluids. Liquid is the most common. The production of hot water with an air-heating collector is usually done in large space-heating systems. It requires the installation of an air-to-water heat ex-
changer in an air duct or inside a rock storage bed. Losses during the heat transfer process are high and air systems do not perform as well as liquid units for heating water. Air systems are generally capable only of preheating water from 70 to 95°F.


Active Solar Systems
In active solar systems, there are a number of factors to be considered. Solar heat may handle space heating or domestic hot water or both. The site must be suitable and the system must be compatible with climate conditions. A back-up system may need to be integrated with the solar system. Sizing the system and storage is critical.




Adjustable Capacitor Banks


Capacitor banks can be designed to correct low PF at different kVA load levels to match the facility’s electrical load. The capacitor bank can be split into several steps of PF correction. Automatic controls are used to change the switching devices. Resonant conditions should be checked using harmonic analysis software before the filter bank is employed. Different combinations of filters are needed to dissipate specific harmonics. The normal procedure is to switch in the lower order filters first, and then add the higher order filters. The procedure is reversed when ilters are removed from service. This is done to prevent parallel resonant conditions that can amplify lower frequency harmonics. These conditions can be caused by the higher frequency filters.


Air Monitoring


Increasingly, legislation is targeted at the monitoring of volatile organic compounds (VOCs) in the atmosphere, many of which are suspected carcinogens or are acutely toxic. Monitoring requirements include rapid, multipoint, multicomponent analysis with the minimum of operator interference. Laboratory analysis can only give a snapshot of pollutants at the time of analysis. It does not analyze exposure to pollutants during a normal working period, nor can it detect sudden chemical leaks.
Thermal desorption involves the adsorption of VOCs on materials over a certain time period followed by desorption and analysis by a gas chromatograph. Thermal desorption only reports the average concentra tion recorded over several hours. It does not detect short-term exposure
to high levels of VOCs.

Air Quality

A BAS can be used to monitor a building’s health and make decisions to prevent the building’s health from degrading. Indoor air quality(IAQ) is important and has received more attention in recent years. The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) has a standard for indoor air quality, (ASHRAE Standard 62-1989, Ventilation for Acceptable Indoor Air Quality). One of the key parts of the standard is the amount of fresh air required per person for various types of building environments. For office environments, the
minimum amount of fresh air is specified to be 20 cubic feet per minute (CFM) per person. This can be used to determine if the quantity of fresh air being introduced is adequate.

Alkaline Fuel Cells

Alkaline fuel cells (AFCs) use hydrogen and oxygen as fuel. The alkaline fuel cell is one of the oldest and most simple type of fuel cell. This is the type of fuel cell that has been used in space missions for some time. Hydrogen and oxygen are normally used as the fuel and oxidant. The electrodes are made of porous carbon plates which are laced with a catalyst to accelerate the chemical reactions. The electrolyte is potassium hydroxide. At the anode, the hydrogen gas combines with hydroxide ions to produce water vapor. This reaction results in electrons that are
left over. These electrons are forced out of the anode and produce the electric current. At the cathode, oxygen and water plus returning electrons from the circuit form hydroxide ions which are again recycled back to the anode. The basic core of the fuel cell consisting of the manifolds,
anode, cathode and electrolyte is called the stack.