programmable thermostats with hot water heating

Rick_13

I'm wondering If there is any advantage to using a programable thermostat in an old house with cast iron column style radiation? Would I be using more fuel trying to heat the house back up after setting the thermostat back? Is there a good themostat to use? If I use a standard mercury style thermostat should I keep the temperature constant all the time.

BillW@honeywell

It depends...

Cast iron radiation has a long flywheel effect, and will continue to emit heat after the boiler and the circs shut down. How much heat your house loses depends on a lot of other factors like insulation, windows, shell material and weather conditions. Our better quality programmable thermostats have a program called "adaptive intelligent recovery" that begins to ramp up the temperature in small increments, so that the comfort setpoint is reached when the "wake" or "return" period begins. An example would be our T8602 series. The old mechanical clocks and the low-end electronic stats like the T8090 or the T8112 just turn the system on at a set time, and sacrifice comfort in many cases.

If you house is tight, has good windows and insulation, or someone is home all the time, an electronic non-programmable thermostat may be your best choice. They feature +-1 degree accuracy and are very easy to use. The T8775 (round digital) or the T8400 (square digital) are mercury free and feature models that can be used for heat only or for heat and air conditioning.

Check them out at www.honeywell.com/yourhome.

Boilerpro_3

Bill's right on

I have used the Chronotherm series with ada;tive recovery on your type of system many times and they work exceptionally well. As to efficiency, the lower the average temperature a structure is kept the lower the heat loss. In addition, most boilers will operate most efficiently with long firing times and long off times. This is exastly the kind of operation you tend to get with your type of system when the thermostat is properly tuned for hot water gravity heat. Using setbacks make these long on times and off times even longer, further boosting efficiency. The only time this might not be true is when using condensing boilers. The low water temps usually associated with gravity systems when maintaining steady temperatures in a home translate to higher boiler efficiencies, which you probably won't achieve if the boiler has to run the system hotter when coming out of setback.

Biolerpro

Uni R

programmable thermostats with hot water heating

As long as the setback period is longer than the period it takes to lose the heat, you will save. Think of it like riding a bike in a valley. If you have to start going back up when you hit the bottom of the hill (the house has to heat back up) you will need to replace all of the energy your house had stored and you will have no gain. If you get to ride for a while in the valley where it is cheaper to heat the house, then you will save money. Also remember to try and keep the setback amount reasonable. Everything in your house expands and contracts at varying rates with changes in the temperature. Drywall screws, the tuning of a piano, hardwood flooring and other similar things don't like change so it is best to keep the setback reasonable.

Matt Undy

Adaptive recovery

How does the adaptive recovery work? Does its algorithm keep some sort of heat loss curve of the building with enough history to account for sudden cold snaps? In other words, does it have an algorithim to track the change in load with change in termpurature even though it is nonlinear? I have the outdoor thermister attached, does it use this information in calculating the recovery load?

Almost all the time it has heated or cooled the house to the setpoint by the set time but we have been having wide variance in tempurater this spring with some highs in the 70's and others in 40's. On one of the 40 degree days the tempurature had only come about half way from the setback point to the recovery point at the return time when I got home from work.

I'm not sure of the exact model but it is a chronotherm about 2-3 years old with 2 stage heat and cool connected to a 2 stage furnace with seperate high and low heat connections (the "professional" model powered from dedicated hot and common from the transformer, not battery powered.). Several contractors(who didnt' get the job) thought i was crazy to use a 2 stage thermostat with a 2 stage furnace....the only time it runs the high stage is on recovery, with the timer in the 2 stage control on the furnace it would be runign high heat frequently and wouldn't heat as evenly.

Thanks

Matt

R. Kalia

cold snaps

> How does the adaptive recovery work? Does its

> algorithm keep some sort of heat loss curve of

> the building with enough history to account for

> sudden cold snaps? In other words, does it have

> an algorithim to track the change in load with

> change in termpurature even though it is

> nonlinear? I have the outdoor thermister

> attached, does it use this information in

> calculating the recovery load?


The outdoor sensor is for displaying outdoor temperature only. Honeywell's Adaptive Intelligent Recovery isn't very intelligent, and it does not handle cold snaps. It jut assumes today is roughly similar to an average of the past few days. But it works OK, it's better than not having it.

Now the sluggishness of hydronic heat isn't only a problem for recovery from setback. You will also get fluctuations when just trying to maintain a set temperature using the start-stop method, because it is like starting and stopping a Mack truck. Many electronic thermostats allow you to set the cycle rate, and hydronic heat works better with a lower cycle rate (typically 3) than forced air (typically 6), but it is not as good as properly tuned anticipation in an analog thermostat.

Of course, outdoor reset is much better than start/stop, but that's not something a thermostat can do.

Mike T., Swampeast MO

Instruction manual for my first Honeywell t-stat with "Intelligent Adaptive Recovery" stated that the unit sensed the temperature of the wall to which it was attached. Instructions said that the unit used the time taken to change the temperature of the wall as part of the algorithm to determine when to start & stop the equipment.

Instructions for later units do not say this and Bill W. at Honeywell once told me that he was unaware of this feature.

BillW@honeywell

The stat \"remembers\"...

what the air temperture has been over the past 3 days, and calculates its recovery based on that. At present the optional outside air temp sensor only give you a display on the stat screen, and has nothing to do with recovery.

If you want a faster responding control that matches the actual demand, try a reset system, "cruise control for your house" that sets the hot water supply temperature based on the outside air temperature. We have the AQ475 that accomplishes this by varying the boiler run time, the AQ675 that controls it by use of a 3 way mixing valve , or the AQ775 that uses a 4 way rotary valve or an injection pump.

doug_10

savings

Give it just what it needs with Exquisite Heat.
www.Exqheat.com
The house will save when it is warm out and heat when it needs it. This way you coast all the time without going up and down.

Firedragon_4

I also agree!

I've had the T8602 since it came out on 1 rad zone, 3 CFBB zones and 1 unit heater zone and all work the nuts, FACT!

The Feds (DOE) say not to take more than one degree of roll-back for each hour of roll-back. I've always done that and recommended it to 1,000's in teaching and in practice, never had a complaint, gotta wonder????