| The concept of heating green roof soil with recaptured condensate from district steam lines, a waste heat source, has been studied at The Cooper Union since 2006, both in New York City and in Iceland, from geothermal sources. Condensate cannot be returned to a central boiler to be reheated, and cooling it to below 65°C avoids the need to mix it with municipal potable cooling water prior to disposal, a common practice. Green roofs with an embedded pipe network can potentially save 3 million m3 of municipal water annually. A heated garden test bed, built to the specifications of a bottom-heated intensive green roof, was built to conduct thermal and controls testing. A ½" type-M copper pipe was embedded into each of 6 parallel, insulated channels; 4 pipes were fitted with female plumbing fittings, allowing for varying piping configurations for a heating fluid to circulate through the test bed, while the 2 remaining pipes and channels served as controls.;In the process of numerical and computational fluid dynamic modeling of heat transfer in the green roof installation, commercial temperature sensors and dataloggers were evaluated. A new datalogging and control system was designed and built, at a much lower cost than traditional process controllers and temperature loggers, to control and record the effects of heating of growth media with discarded steam condensate in a pipe network. This system used discrete analog temperature sensor ICs interfaced with an ATmega microcontroller-based Arduino board. Arduino is an open source microcontroller project framework, and an Arduino board, with microcontroller, retails for about ;Different temperature sensors were used at different stages, including thermistors, k-type thermocouples, and LM335 temperature-sensing ICs. A large number of readings - 20 or more - with sufficient accuracy and at a reasonable price and setup time expenditure, was obtainable with the LM335 alone, when interfaced with the Arduino datalogging controller.;Runs were conducted to control soil temperature and simultaneously log point temperatures, using a specially designed relay actuator and an on-off control program running on the Arduino microcontroller, and a serial interface between the controller and a desktop computer. A proxy, written in the Processing programming environment, receives temperatures sent from the Arduino and logs them, with a timestamp, in a file on the computer.;Sensor offset complicated the verification of the final datalogging and temperature control product, but the most probable cause, excessive current draw, will be resolved with the addition of a power supply and voltage regulator. Incorporating a soil moisture sensor will enable the installation of a rooftop drip irrigation system that repurposes cooled condensate or collected rainwater. |
