What's the difference between a warm weather shut down and an outdoor reset

trisha

Hi,

I think this might be an embarrassingly simple question, but I can't sort it out from looking on line.

Here's the scenario - I'm trying to find a better boiler control for a multi-family building using a steam heat system.  Currently, a reliable tenant on the first floor has control of the thermostat for the whole building.  The thermostat sensor is located, via hard-wiring, in a third floor (apartment building is 4 floors) apartment so that the system will call for heat until the temperature there is satisfied.

The set up is not working well - complaints of overheating when the heat is on, as well as times when the building is cold and the heat isn't coming up.  When the latter happens, I have to call the tenant on the first floor and ask them to bump up the heat.

Both an outdoor reset and a warm weather shut down have been recommended.  I don't understand the difference between these two methods- can anyone explain to a lay person, as well as given any thoughts on which you think would be best for my scenario?

It was also recommended to me to install TRVs in all apartments.  Given the cost of each unit and the number of radiators, that suggestion isn't doable financially right now, but might make sense later, in case that changes anyone's recommendations.

thanks in advance!

Mike Kusiak_2

Steam system control

Both of these terms relate to a steam system controller which depends on outdoor temperature to control the boiler. They are both typically incorporated into the same control unit and function by means of the same outdoor temperature sensor.



Warm weather shut down ( WWSD) is a function which shuts down the boiler whenever the outdoor temperature rises to a preset level. This would typically be a temperature where heat is no longer necessary, say 55 to 60 degrees.



Outdoor reset (ODR) is a function where the length of the steam cycle is varied according to outdoor temperature. For example on a 20 degree day the boiler may run each hour for 30 minutes and then shut off. On a 50 degree day the boiler may operate only 10 minutes each hour.  As the outside temp changes, the cycles change in length, calibrated to the characteristics of the building. Typically there is no indoor thermostat at all, although some systems may allow for some indoor temperature sensors to avoid overheating.



Keep in mind that these systems will not even out the heating in the various apartments. If some are too cold and some too hot this problem will be unchanged. Typically the system is set to satisfy the coldest apartment and the hotter ones can turn off radiators or use thermostatic radiator valves to limit room temperatures.



The Tekmar 279 is a controller which performs these functions and has been highly recommended, although it is somewhat expensive compared to a regular thermostat

nicholas bonham-carter

A little balance

If your radiators are heating unevenly, then it needs to be balanced, usually by correcting the main venting. Have you owned this building long? Certainly, when first built, the system was perfectly even. Therefore the task is to return the system to its original state of operation, with low pressure, ample venting, and good thermostatic control with a steam certified thermostat. Is this a 1-pipe, or 2-pipe system?

A sophisticated control will not compensate for these sorts of problems, and may only exaggerate them.

What sort of thermostat are you using, and has it been configured for steam?--NBC

trisha

thanks and more questions

Hi Mike, thanks for your reply.  If I understand correctly, the WWSD and the outdoor reset are not mutually exclusive control systems, but rather compliment each other, right?  Based on your answer, though, it seems like the outdoor reset could take care of limiting (but maybe not totally shutting down? like the WWSD) the boiler when the outdoor temperature is mild, so that you might not need the WWSD.  On the other hand, the WWSD would take care of eliminating wasteful heating when it wasn't needed but wouldn't do anything for my problem of inadequate heating when the outdoor temperatures are bitter.  So a WWSD alone wouldn't solve my problem, right?

Does the Tekmar system include both functions?  It was mentioned to me, along with a redlink thermostat system.  I don't understand how a sensor inside the apartment would work with the outdoor reset system - does the system accept two sets of information (i.e., the temperature inside the apartment and the temperatures outside) or does one set of information override the other?



I guess at the most basic, I'm trying to figure out if I need 1, 2 or 3 (outdoor reset, WWSD and redlink)

trisha

ok, just read your answer again

sorry mike, didn't read carefully the first time - I understand now that both a WWSD function and a outdoor reset are functions within a single controller.  I think the plumber I was speaking with was using the terms interchangeably and that was confusing me into thinking they were two separate types of control systems.

Still curious though as to how a internal temperature sensor can be incorporated into this type of system?

trisha

thanks for your answer

Hi Nicholas,

thanks for your answer.  I've owned the building for 15 years and the heating season has always been a challenge.  For some reason, this is the year I've decided to fix it

It's a single pipe system.  By main venting, I assume your are talking about the first set of pipes coming off the boiler?  The plumber I consulted with pointed out some problems with the installation (the headers are too small apparently) which I plan to resolve when weather and financing permits. 

Currently, the thermostat control is just a regular Honeywell programmable type with a sensor installed on a higher up floor.  Needless to say, lots of problems with this arrangement.  I'm uncertain whether this thermostat has been "set" for a steam system - an electrician installed it and I'm not certain if he did this or was even aware that it was necessary.

Mike Kusiak_2

Tekmar 279

Yes, the Tekmar provides both ODR and WWSD functions. It also has the ability to be used with indoor temperature sensors if desired.



Here is a link to the operation and installation manual which goes into detail regarding how to set it up and indoor sensing:



http://tekmarcontrols.com/images/_literature/279_d_06.pdf

mcsteamy

Saving money

You are going to burn a lot more cash screwing around with outdoor resets and advanced boiler controls than you will just getting this building heated evenly.  Those controls allow you to precisely dial in an already decent system and get rid of the guy in the basement that used to pull the switches on a large commercial system.  They won't fix a mess.  And you have a mess.



Buy The Lost Art of Steam Heating as a first step to understanding what you are doing probably better than the people working on your system. 



Then, vent your main steam lines FAST.  Then use a combination of properly sized radiator vents and, if absolutely necessary, TRVs, to get the whole thing in balance.  Of course, Lost Art will tell you all of this.