Summer /Winter switches

enthalpy

Professor,
PLEASE!! explain the purpose of a manual switch over for heating and cooling.Have been having trouble with these this week and my guru is on vacation. For the most part the switches are use with boilers and HWC and the fan runs contantly.
Also they are using a three way valve to modulated the water with a pump that runs continiously.
Need some help with troubleshooting these systems.

Eugene Silberstein 3

Summer/Winter Switches

Summer/winter switches originally became popular a few generations ago, when air conditioning systems were in their infancy. Technicians typically worked on heating systems and, when coling was added to the mix, posed a number of wiring nightmares for those not in the know. The easiest way to avoid having to design intricate control circuits was to wire the cooling and the heating systems separately and control them manually with sets of ON-ON switches that would be used to manually switch the system over from heating to cooling and vice versa.

Nowadays, summer winter switches are commonly found on commercial systems that have a fair number of automatically controlled valves/dampers and other flow devices. Consider this example. Let's say there is a thermostatically controlled valve that controls water flow through a duct-mounted coil. This coil is being used to handle hot water in the winter months and chilled water in the summer months. Now, for smaller applications, it is an easy solution to circulate the water (either heated or chilled) through the coil constantly and cycle the fan on and off in response to the space temperature requirements.

In larger commercial applications, constant airflow is needed, given the fact that a certain percentage of outside air must be introduced to the space. So, the fan must remain on all the time. Well, if the fan is on all of the time and there is constant flow throug the coil, the space will be overheated in the winter and overcooled int he summer. Enter the modulating valve.

The modulating valve controls (starts, stops or adjusts) the amount of water (heated or cooled) that flows through the coil. The circuits that are used to control the positioning of the valve are different depending on the mode of operation. By providing a manual switch (summer/winter), we are basically changing the set of instructions that the valve will follow.

What I have described is only one possible scenario, as there are many control strategies that utilize the manual changeover switch.

Hope this helps.