June 2012 Issue (files are in PDF format)
The IPCC report on climate change mitigation.
Test Bed buffer
For heating, there is a much larger demand at night than during the day so the buffer accumulates heat during the day and then gives it up at night. That levels the power load - the ground heat exchanger would otherwise need to be much larger to handle the peak load. It also reduces the power consumption because the heat pump does not need to struggle to extract heat from a cold supply line. The buffer has two modes: a trickle supply mode that handles the diurnal load fluctuations and a surge mode that handles the abrupt ON-OFF cycles of the heat pump.
For cooling, the sequence is similar. During the day the heat from the house is temporarily transferred into the buffer and then at night it is transferred into the ground. Without the buffer the ground heat exchanger temperature would rise during the day to a value that would substantially reduce the COP of the heat pump. The use of the buffer makes it possible to reduce the length of the ground exchange pipes - freeing up most of those pipes so that they can be used to inject additional heat into the ground from the air heat exchanger.
For the winter of 2011/2012 the addition of the buffer made it possible to operate the test bed system without ever having to resort to the use of the electric heating coil in the air handler.