New steam control principle

nicholas bonham-carter

I wonder if the sort of outdoor reset used with tekmar and heattimer would work better if the outdoor sensor were attached to an outside north wall to monitor the difference between wall temperature and air temperature. It might feel the difference between 10 degrees with and without a 40 mph wind. It would also react to the presence of or lack of insulation in the walls.--NBC

SWEI

not sure exactly what you're describing

but an outdoor air temperature sensor is almost always installed on a north wall.  Here in the southwest, we sometimes put them on a northeast corner, which allows them to anticipate mid-morning sun before it comes streaming in and overheats the space.



An uninsulated building leaks more heat to the outside, which could increase the measured temp above actual ambient (lowering the heat delivery rate.)

nicholas bonham-carter

Modified reset principle

I am thinking the new control would compare the temperatures of a outside north wall from the inside; and the ambient air temperature in the same room. If there were a wind blowing, the temperature of the outside wall would drop more quickly than if the air were still.

By comparing these temperatures, the runtime could be computed.

The regular outdoor sensor cannot react to wind, which must play a major part in heat loss. This would also take account of the Rvalue of the wall.

I do not have that sort of control for my 55 radiator system, but have thought about it. For the moment, a Honeywell vision pro with remote sensor in a cooler north 2nd floor apartment seems to work well. I just wish I could average a couple of sensors, but then I would need the tekmar 279, with it's learning curve, and outdoor sensor.--NBC

SWEI

DDC

Can handle easily this, and more.  Think of a reset algorithm that takes into account wind speed, multiple OAT sensors (to predict demand in specific building areas), and even weather forecasts.

sreja

re: New steam control principle

nbc,



We've talked about this idea before.  I started a thread here about how wind has a dramatic affect on the heating requirements of our poorly insulated building:



http://www.heatinghelp.com/forum-thread/135308/Low-tech-ways-to-adjust-outdoor-temp-sensor-based-on-wind



I ended up implementing this with our tekmar control.  The tekmar lets you set up INDOOR temperature sensors as well as an outdoor sensor.  I set up an indoor sensor in a barely heated garage space next to a drafty window.  The result is that the indoor sensor reflects the heat loss due to wind in the rest of the building.

nicholas bonham-carter

Tekmar sensors

Yes that is the sort of thing I was contemplating, but inside the conditioned space.

I thought the tekmar needed an indoor sensor (inside the heated area), in order to function as an upper limit. I probably need to reread the documentation in order to understand this better, (and your thread).

SW, what is DDC?--NBC

SWEI

Direct Digital Control

Microprocessors running software written or tailored specifically for the building and tasks.



Most commonly found in large commercial and industrial settings.

Dave in QCA

Tekmar

nbc, I think that the Tekmar may already do what you are thinking, more or less.  I have my outdoor sensor installed on the north side of the building.  Since the building is stucco, it is attached and edge of a basement window jam about 3 feet above grade.  The window has a storm on it and I don't think it leaks much, but since the sensor is in a little nook by a window, it tends to read warmer than the actual ODA temp when there is no wind.  When there is a north wind, the sensor will read the ODA precisely correct.   So, the Tekmar is seeing a warmer or colder temperature dependent on whether the wind is blowing.  But, this is a minor effect, maybe five degrees ODA temp and this would have a small yet real effect on the cycle length.



Indoor sensors provide the correction that is needed to compensate for wind, sun, cloudy days, etc.   Keep in mind, the Tekmar runs just fine with the standard 2 sensors.  One is the ODA sensor and the other is located at the end of the steam main.  The outdoor air temperature tells the Tekmar how long the on cycle should be.  The end of main sensor tells the Tekmar when steam has been established and that is the beginning of the cycle time.  The older heattimers functioned with only these two sensors, but I think they have improved the design in the new models by adding the option of indoor sensors.  Tekmar provides for input from one or two indoor sensors.  Actually, you can add mutiples as well and they will average, but lets keep it simple for this explanation.  I have two indoor sensors, on in the downstairs north and one in the downstairs south.  Depending on whether it is sunny, cloudy, windy, etc., the south room might be the coldest, but more often than not, the north room is the coldest.  Tekmar gives the option of selecting one sensor or both, I choose both.  It also gives the option of averaging the two, or picking the coldest of the two.  I pick the coldest.  So, the Tekmar then looks at the coldest sensor to see whether that space temp is the same as the room target.  If it is, then the cycle length will be the normal calculated length, the same as if I had no indoor sensors.  But, we all know that things drift, especially with changing weather.  If the indoor temp begins to drift upward, the cycle lenght will be adjusted downward.  if the room temp begins to drift downward, the cycle lenght will be increased slightly.  Thus, it is the feedback from the coolest room sensor that fine tunes the cycle lenght, and this alone compensates for wind or no wind and maintaines a very stable and smooth space temperature.



The hard thing to grasp in this system is that the main controller never runs the boiler to directly satisfy the indoor sensor in the manner that a thermostat does.   



If it were possible to create a digital thermostat, that had a sensor on the end of the steam main so it could know when steam was established, and this would be used to activate an anticipator circuit.  And, if the anticipator circuit was intelligent and was linked to the outdoor air temperature which would adjust the amount of anticipation, so that it would not tend to overshoot in mild weather and also would not undershoot in cold weather.  If such a thermostat existed, its performance in terms of space temperature control would be very much the same as the Tekmar, although the way in which it would achieve a steady space temperature control would be different because of actually running the boiler to satisfy the thermostat.



Hope this helps. 

Hap_Hazzard

Does anybody make a sensor...

you can stick on your wife's forehead so the system can tell when she's too cold, when she's having a hot flash or when she's doing housework or sitting on the couch watching Desperate Housewives? That's what I need.



I have things pretty well balanced, except for the room with the electric baseboard that I never turn on, so the temperature is always 70°, give or take a degree, but my wife is always either too hot or too cold. It's pretty clear her thermostat is haywire, but they don't sell replacements for those, so I need a sensor that can tell when it's acting up and anticipate how she's going to be feeling and adjust the heat accordingly.

SWEI

mean radiant temperature

Thermostats measure air temperature.



At least 50% of the body's temperature perception is radiant.  Get an infrared thermometer and point it at the walls, windows, ceiling, and floor next time she's cold.  I suspect you will come to understand more about your house and its heating system.

Hap_Hazzard

I have a couple of those.

I've been using one of them to trace where they ran the pipes when they built the addition to our house. I have noticed that the walls are cooler than the air, but that's not surprising since they didn't bother to insulate anything.

SWEI

add them up

and compute an average.  Single-pane windows will really drag that number down on a cold night.



Measuring the little house where we are currently staying one recent night, I got the following temps:



73.8F  interior partition wall with the stat (south end of that room)

70.1F  ceiling

68.5F  east facing wall with front door

67.2F  west facing wall

66.6F  north facing wall between two large steel casement corner windows.

52.4F  north facing casement window