[mh] HVAC Wiring Help

[Jim Duda <jim@du...>]

Hi,

This is a long winded email, with 3 HVAC question below.  Thanks for you 
patience with this one.

I had a central A/C system installed a couple of days ago.  I have an 
external compressor and an air handler in the attic.  I also have oil 
fired furnace for forced hot water heat in the basement.  I only have a 
single zone system.  My house has two floors.

Obviously, I want misterhouse to control the A/C.  MH currently controls 
the heat.  I have 5 1-wire thermometers distributed across the house. 
Although it's a one zone system, the different thermometers allow me to 
sensitize the trip points based upon time-of-day.

I have a 1-wire relay to close the heat relay.  I have a 1-wire relay 
ready for A/C control too.

The A/C was installed with a new thermostat, which was placed upstairs 
near the air return.  The new thermostat was installed with three wires, 
RED, YELLOW, and GREEN.

I've read the thermostat wiring chart.  I believe the RED is the 24 A/C 
power feed, the YELLOW is the control for the compressor, and the GREEN 
is the control for the fan.  The thermostat has an ON/AUTO switch for 
the fan control.

I believe that when the switch is set to AUTO and the thermostat trips, 
the thermostat will close a relay between RED-YELLOW to call for the 
compressor and it simultaneously closes a second relay between RED-GREEN 
to turn on the FAN.  I believe when the switch is set to ON, the 
thermostat simply closes the relay between RED-GREEN to operate the fan 
only.  Do I understand correctly?

I honestly don't think I'll ever have a need for FAN ONLY.  I would 
expect to always operate the system in AUTO mode always.

Question(s) #1:

For MH control, can I use a single 1-wire relay for the A/C control?  C

Can I simply connect YELLOW and GREEN together and attach the RED to one 
side of the 1-wire relay and the YELLOW/GREEN pair to the other side of 
the relay?

Do I really need two 1-wire relays, for GREEN and YELLOW separately?

Question #2:

I now have thermostats in both the first and second floors of my house. 
  The thermostat on the first floor controls the heat, and the 
thermostat on the second floor controls the A/C.

I have the first floor thermostat wired in parallel with the 1-wire 
relay.  So, either MH or the thermostat can call for heat.  The 
thermostat is normally OFF, allowing MH to control the heat.  The 
thermostat is a backup in the event MH goes down.

I expect the same for the second floor thermostat.  I want to wire the 
second floor thermostat in parallel with the A/C 1-wire relay, shorting 
YELLOW/GREEN together at the 1-wire relay.

Is this okay?

Question #3:

Is it okay to wire both thermostats and MH all in parallel such that I 
can control heat and/or A/C from either thermostat or MH, normally 
operating both thermostats in the OFF position and only operating one 
thermostat in the event of a MH failure?

Having the thermostats are a must when I sell the house someday :-)

Thanks for your patience,

Jim

[mh] HVAC Wiring Help

[Jim Duda <jim@du...>]

Hi,

This is a long winded email, with 3 HVAC question below.  Thanks for you 
patience with this one.

I had a central A/C system installed a couple of days ago.  I have an 
external compressor and an air handler in the attic.  I also have oil 
fired furnace for forced hot water heat in the basement.  I only have a 
single zone system.  My house has two floors.

Obviously, I want misterhouse to control the A/C.  MH currently controls 
the heat.  I have 5 1-wire thermometers distributed across the house. 
Although it's a one zone system, the different thermometers allow me to 
sensitize the trip points based upon time-of-day.

I have a 1-wire relay to close the heat relay.  I have a 1-wire relay 
ready for A/C control too.

The A/C was installed with a new thermostat, which was placed upstairs 
near the air return.  The new thermostat was installed with three wires, 
RED, YELLOW, and GREEN.

I've read the thermostat wiring chart.  I believe the RED is the 24 A/C 
power feed, the YELLOW is the control for the compressor, and the GREEN 
is the control for the fan.  The thermostat has an ON/AUTO switch for 
the fan control.

I believe that when the switch is set to AUTO and the thermostat trips, 
the thermostat will close a relay between RED-YELLOW to call for the 
compressor and it simultaneously closes a second relay between RED-GREEN 
to turn on the FAN.  I believe when the switch is set to ON, the 
thermostat simply closes the relay between RED-GREEN to operate the fan 
only.  Do I understand correctly?

I honestly don't think I'll ever have a need for FAN ONLY.  I would 
expect to always operate the system in AUTO mode always.

Question(s) #1:

For MH control, can I use a single 1-wire relay for the A/C control?  C

Can I simply connect YELLOW and GREEN together and attach the RED to one 
side of the 1-wire relay and the YELLOW/GREEN pair to the other side of 
the relay?

Do I really need two 1-wire relays, for GREEN and YELLOW separately?

Question #2:

I now have thermostats in both the first and second floors of my house. 
  The thermostat on the first floor controls the heat, and the 
thermostat on the second floor controls the A/C.

I have the first floor thermostat wired in parallel with the 1-wire 
relay.  So, either MH or the thermostat can call for heat.  The 
thermostat is normally OFF, allowing MH to control the heat.  The 
thermostat is a backup in the event MH goes down.

I expect the same for the second floor thermostat.  I want to wire the 
second floor thermostat in parallel with the A/C 1-wire relay, shorting 
YELLOW/GREEN together at the 1-wire relay.

Is this okay?

Question #3:

Is it okay to wire both thermostats and MH all in parallel such that I 
can control heat and/or A/C from either thermostat or MH, normally 
operating both thermostats in the OFF position and only operating one 
thermostat in the event of a MH failure?

Having the thermostats are a must when I sell the house someday :-)

Thanks for your patience,

Jim

Re: [mh] HVAC Wiring Help

[Jim Serack <jserack@sy...>]

I'm no expert but here are some thoughts.


-----Original Message-----
From: misterhouse-users-bounces@...
[mailto:misterhouse-users-bounces@...] On Behalf Of =
Jim
Duda
Sent: July 28, 2007 9:33 AM
To: misterhouse-users@...
Subject: [mh] HVAC Wiring Help


Hi,

This is a long winded email, with 3 HVAC question below.  Thanks for you =

patience with this one.

I had a central A/C system installed a couple of days ago.  I have an=20
external compressor and an air handler in the attic.  I also have oil=20
fired furnace for forced hot water heat in the basement.  I only have a=20
single zone system.  My house has two floors.

Obviously, I want misterhouse to control the A/C.  MH currently controls =

the heat.  I have 5 1-wire thermometers distributed across the house.=20
Although it's a one zone system, the different thermometers allow me to=20
sensitize the trip points based upon time-of-day.

I have a 1-wire relay to close the heat relay.  I have a 1-wire relay=20
ready for A/C control too.

The A/C was installed with a new thermostat, which was placed upstairs=20
near the air return.  The new thermostat was installed with three wires, =

RED, YELLOW, and GREEN.

I've read the thermostat wiring chart.  I believe the RED is the 24 A/C=20
power feed, the YELLOW is the control for the compressor, and the GREEN=20
is the control for the fan.  The thermostat has an ON/AUTO switch for=20
the fan control.

I believe that when the switch is set to AUTO and the thermostat trips,=20
the thermostat will close a relay between RED-YELLOW to call for the=20
compressor and it simultaneously closes a second relay between RED-GREEN =

to turn on the FAN.  I believe when the switch is set to ON, the=20
thermostat simply closes the relay between RED-GREEN to operate the fan=20
only.  Do I understand correctly?

----> That is how mine works - two sets of 28V relays in the actual unit
controlled by the relays in the thermostat. I did have one "cheap"
electronic thermostat in which the "auto" switch just directly connected =
the
green connection to yellow wire connection which was driven by a relay.
Watch for that.

I honestly don't think I'll ever have a need for FAN ONLY.  I would=20
expect to always operate the system in AUTO mode always.

Question(s) #1:

For MH control, can I use a single 1-wire relay for the A/C control?  C

Can I simply connect YELLOW and GREEN together and attach the RED to one =

side of the 1-wire relay and the YELLOW/GREEN pair to the other side of=20
the relay?

Do I really need two 1-wire relays, for GREEN and YELLOW separately?

----> I would have the two - I operate my fan sometimes just to equalize =
the
temperature within the house
Without running the compressor. (e.g. early morning - sun in the office,
cool in the kitchen)

----> Make sure for the mh AC compressor control you read about minimum
compressor cycle times, including the miminum "off" time between cycles =
to
avoid compressor stall and premature wear out.

Question #2:

I now have thermostats in both the first and second floors of my house.=20
  The thermostat on the first floor controls the heat, and the=20
thermostat on the second floor controls the A/C.

I have the first floor thermostat wired in parallel with the 1-wire=20
relay.  So, either MH or the thermostat can call for heat.  The=20
thermostat is normally OFF, allowing MH to control the heat.  The=20
thermostat is a backup in the event MH goes down.

I expect the same for the second floor thermostat.  I want to wire the=20
second floor thermostat in parallel with the A/C 1-wire relay, shorting=20
YELLOW/GREEN together at the 1-wire relay.

Is this okay?
-----> I would not. Use two relays since if someone did decide to just =
run
the fan using the thermostat it would also turn on the compressor - with =
no
thermostatic function! - deep freeze (until your heater cut in).
You would have to set the thermostat to off - or a very high temperature =
to
normally keep it from controlling the temperature since they are in
parallel.

Question #3:

Is it okay to wire both thermostats and MH all in parallel such that I=20
can control heat and/or A/C from either thermostat or MH, normally=20
operating both thermostats in the OFF position and only operating one=20
thermostat in the event of a MH failure?

-----> I would say electrically yes - but from an operating perspective =
you
would be creating a very confusing system for someone to determine which
device is actually controlling the temperature. You also run the risk of
calling for heat and AC at the same time from different controllers - I
think at least once you'll be saying what the heck?

Having the thermostats are a must when I sell the house someday :-)

----> Have you thought about going to a thermostat with a serial or 1 =
wire
input? Let mh control the thermostat and the thermostat control the AC =
and
heating equipment?
http://www.asihome.com/ASIshop/product_info.php?products_id=3D1291
http://www.smarthome.com/_/Thermostats_HVAC_Controls/Thermostats/_/J/1Sr/=
nav
.aspx

Thanks for your patience,

Jim



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Re: [mh] HVAC Wiring Help

[Tim Sailer <tps@ma...>]

One thought, having designed industrial systems like this, controlled by
computer:

ALWAYS have a mechanical failsafe.

For your heat, have a reliable 'normal' mechanical stat set in the
building somewhere  that can force the heat on at 40F.

For AC, make sure you have a mechanical stat for AC to open the circuit at
60F unless you want to hang meat, or you have stock in the utilities.

If you are venting the house, (attic or whole house) make sure you turn
off the fan if the temp goes to above 140F, as you will just be fanning
the fire at that point that's burning somewhere in the building.

Tim

--
Tim Sailer
Coastal Internet, Inc.
 http://www.buoy.com
631-399-2910

Re: [mh] HVAC Wiring Help

[<satz@ir...>]

> ----> Have you thought about going to a thermostat with a serial or 1 wire
> input? Let mh control the thermostat and the thermostat control the AC and
> heating equipment?
> http://www.asihome.com/ASIshop/product_info.php?products_id=1291
> http://www.smarthome.com/_/Thermostats_HVAC_Controls/Thermostats/_/J/1Sr/nav
> ..aspx

This is what I do. I let the thermostats do what they do best and just
create setpoints when to turn on heat/cool. I use the thermostats from
http://www.homeauto.com which talk to my security system from the same
company. These thermostats will also do rs232. Aprilaire also has
thermostats which will allow you to control them.

Thanks,
Greg

Re: [mh] HVAC Wiring Help

[Jim Duda <jim@du...>]

Thanks for all the posts everyone.

I'm up and running now, with MH controlling the A/C

1) I went with two 1-wire relays, one for FAN and another for COMPRESSOR
2) I added a timer to insure that there is 3 minutes between OFF and ON 
states to avoid compressor issues.
3) I wired MH in parallel with both upstairs and downstairs thermostats, 
however, left the upstairs and downstairs thermostats separated with 
upstairs controlling cool and downstairs controlling heat.

Jim

Jim Duda wrote:
> Hi,
> 
> This is a long winded email, with 3 HVAC question below.  Thanks for you 
> patience with this one.
> 
> I had a central A/C system installed a couple of days ago.  I have an 
> external compressor and an air handler in the attic.  I also have oil 
> fired furnace for forced hot water heat in the basement.  I only have a 
> single zone system.  My house has two floors.
> 
> Obviously, I want misterhouse to control the A/C.  MH currently controls 
> the heat.  I have 5 1-wire thermometers distributed across the house. 
> Although it's a one zone system, the different thermometers allow me to 
> sensitize the trip points based upon time-of-day.
> 
> I have a 1-wire relay to close the heat relay.  I have a 1-wire relay 
> ready for A/C control too.
> 
> The A/C was installed with a new thermostat, which was placed upstairs 
> near the air return.  The new thermostat was installed with three wires, 
> RED, YELLOW, and GREEN.
> 
> I've read the thermostat wiring chart.  I believe the RED is the 24 A/C 
> power feed, the YELLOW is the control for the compressor, and the GREEN 
> is the control for the fan.  The thermostat has an ON/AUTO switch for 
> the fan control.
> 
> I believe that when the switch is set to AUTO and the thermostat trips, 
> the thermostat will close a relay between RED-YELLOW to call for the 
> compressor and it simultaneously closes a second relay between RED-GREEN 
> to turn on the FAN.  I believe when the switch is set to ON, the 
> thermostat simply closes the relay between RED-GREEN to operate the fan 
> only.  Do I understand correctly?
> 
> I honestly don't think I'll ever have a need for FAN ONLY.  I would 
> expect to always operate the system in AUTO mode always.
> 
> Question(s) #1:
> 
> For MH control, can I use a single 1-wire relay for the A/C control?  C
> 
> Can I simply connect YELLOW and GREEN together and attach the RED to one 
> side of the 1-wire relay and the YELLOW/GREEN pair to the other side of 
> the relay?
> 
> Do I really need two 1-wire relays, for GREEN and YELLOW separately?
> 
> Question #2:
> 
> I now have thermostats in both the first and second floors of my house. 
>   The thermostat on the first floor controls the heat, and the 
> thermostat on the second floor controls the A/C.
> 
> I have the first floor thermostat wired in parallel with the 1-wire 
> relay.  So, either MH or the thermostat can call for heat.  The 
> thermostat is normally OFF, allowing MH to control the heat.  The 
> thermostat is a backup in the event MH goes down.
> 
> I expect the same for the second floor thermostat.  I want to wire the 
> second floor thermostat in parallel with the A/C 1-wire relay, shorting 
> YELLOW/GREEN together at the 1-wire relay.
> 
> Is this okay?
> 
> Question #3:
> 
> Is it okay to wire both thermostats and MH all in parallel such that I 
> can control heat and/or A/C from either thermostat or MH, normally 
> operating both thermostats in the OFF position and only operating one 
> thermostat in the event of a MH failure?
> 
> Having the thermostats are a must when I sell the house someday :-)
> 
> Thanks for your patience,
> 
> Jim
> 
> 
> 
> -------------------------------------------------------------------------
> This SF.net email is sponsored by: Splunk Inc.
> Still grepping through log files to find problems?  Stop.
> Now Search log events and configuration files using AJAX and a browser.
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>