On 1/1/2012 12:24 AM, Ignoramus21023 wrote:
On 2012-01-01, The Daring wrote:
On 12/31/2011 9:10 PM, Ignoramus21023 wrote:
I have a commercial building with about five thermostats for
heating. They are of the non-smart variety, maintaining the same
temperature regardless of time of day, with only a pair of 24v
contacts leading to them.

Given that it is a 10,000 square foot building, this is costing me a
lot of money spent on unnecessary heating during nighttime.

During the day, I want the temp to be 47 degrees, and at night, I
would be happy with 38 degrees or so.

Do programmable thermostats need a separate power supply, or can they
run themselves from just a pair of 24v wires that they open and close?

In other words, if I buy and install programmable thermostats, will I
have to run any additional wiring?

Thanks
i

Most electronic thermostats have a battery compartment for two AA or AAA
batteries with an option for powering the T-stat from the 24 volt supply
but you usually find more than 2 conductors in a thermostat cable. Most
thermostat cable has 5 wires colored white, red, green, blue and yellow.
Normally red is the hot wire with blue being ground or common. A
mechanical heat/cool thermostat will use all but the blue wire. A heat
only thermostat will use red and white but green will used if the fan
can be turned on without the heat. Unit heaters, the type you may see
hanging from the ceiling in a lot of warehouses are usually controlled
using only two conductor cable. A programmable thermostat can work with
a two wire system if you remember to change the batteries once a year.

TDD

If it is once a year or even once per quarter, I can live with it.
I put a residential type Honeywell thermostat in my motor home. As
there really isn't any 24 volts, AC, it runs off the internal batteries
switching 12 volts DC. The batteries will last the entire summer season
but may die sometime before doing the spring cleanup. Actually,
sometimes they are still good in the spring. It sounds like your
application is in a storage warehouse, or something similar. Is it
possible to just use one thermostat at night, set to the low temp, to
switch on and off the 24 volts to all the individual thermostats which
are set to the higher temp? As we don't know the application and how
critical the evenness of temperature is, this was just a light bulb idea.