Rethinking TRVs for Steam Heating Systems

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Rethinking TRVs for Steam Heating Systems

Rethinking thermostatic radiator valves for steam heating systems

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nicholas bonham-carter

A little more elaboration of how to size the boiler using some comparison of the connected load, and the heatloss would be more informative.--NBC

john walsh_2

I totally agree with his last point. Oversized radiators do not need to be nor should be heated all the way across. Sizing the boiler using a heat loss calculation and generous pickup factor coupled with good main and riser venting and then venting the radiators according to the room's needs is a better way to go. Smart guy! :-)

Dave Stroman

I learn something new on every steam system I work on or install. It is a joy to get a system to work when no one else could. It is info like this that makes "us" so valuable.

ChrisJ

john walsh said:

I totally agree with his last point. Oversized radiators do not need to be nor should be heated all the way across. Sizing the boiler using a heat loss calculation and generous pickup factor coupled with good main and riser venting and then venting the radiators according to the room's needs is a better way to go. Smart guy! :-)

Everyone pushing for automatically oversizing a boiler by 33%, or even 50% above the installed radiation which is often oversized for the heatloss of the space is enough to drive someone to drink. Isn't it John?

In my opinion, the heatloss, piping losses and radiation should all be considered. Sizing a steamer properly is an art and when done correctly performs beautifully, even during a recovery. Venting is of course just as important and not only does the size of the radiator and heatloss of the room matter, but the distance from the boiler does as well.

When all is done correctly, the system will work wonderfully. When it's rushed and done wrong, it's a disaster. Unlike forced air, you can't just open a door to correct for a mistake.


One thing I found with my tiny residential system and two TRVs was the more cycles, the better. If a system is only cycled once per hour, the TRVs do not have much control, resulting in large temperature swings. 2 cycles per hour is a substantial improvement and 3 cycles per hour works really nice. This seems like it would be very important when running a system such as the Tekmar 279 in a large building. Like an apartment building where the TRVs are doing most of the throttling in the individual units and the boiler is running based on outdoor temperature rather than indoor temperature. This is of course assuming it's a single pipe system.

john walsh_2

@ChrisJ I remember sizing the boiler on the first job I ever did. It was a 3 family in Brooklyn. I did a great job on sizing the boiler on the radiator's EDR but I never, due to a lack of experience, considered the pickup factor. Needless to say, the boiler was too small to heat all the rads all the way across and I had cold rooms. It was really disappointing. But then I realized that some of the rads were over sized and overheating their spaces, while others only heated up to about a quarter way across. That's when I started playing with the venting. It took some doing, but I got the system balanced in terms of even heat output, the boiler heats the space rather quickly and the fuel bills are low. I learned a lot during that experience.

Jack M

john walsh said:

@ChrisJ I remember sizing the boiler on the first job I ever did. It was a 3 family in Brooklyn. I did a great job on sizing the boiler on the radiator's EDR but I never, due to a lack of experience, considered the pickup factor. Needless to say, the boiler was too small to heat all the rads all the way across and I had cold rooms. It was really disappointing. But then I realized that some of the rads were over sized and overheating their spaces, while others only heated up to about a quarter way across. That's when I started playing with the venting. It took some doing, but I got the system balanced in terms of even heat output, the boiler heats the space rather quickly and the fuel bills are low. I learned a lot during that experience.

Is it worthwhile following up on the notion of "heating up quickly?" In John Walsh's assessment of performance he mentions "the boiler heats the space rather quickly..." and often this is used as a measure of performance. Homeowners want a system that responds to their needs, but are we misleading them (or ourselves). Is a rapid change in room temperature a red flag for steam systems? Where does response time fit into the equation?

ChrisJ

Jack M said:

john walsh said:

@ChrisJ I remember sizing the boiler on the first job I ever did. It was a 3 family in Brooklyn. I did a great job on sizing the boiler on the radiator's EDR but I never, due to a lack of experience, considered the pickup factor. Needless to say, the boiler was too small to heat all the rads all the way across and I had cold rooms. It was really disappointing. But then I realized that some of the rads were over sized and overheating their spaces, while others only heated up to about a quarter way across. That's when I started playing with the venting. It took some doing, but I got the system balanced in terms of even heat output, the boiler heats the space rather quickly and the fuel bills are low. I learned a lot during that experience.

Is it worthwhile following up on the notion of "heating up quickly?" In John Walsh's assessment of performance he mentions "the boiler heats the space rather quickly..." and I think that often this is used as a measure of performance. Homeowners want a system that responds to their needs, but are we misleading them (or ourselves). Is a rapid change in room temperature a red flag? Where does response time fit in the equation?

I don't know, but the main reason I converted my EG-45 down to an EG-40 was to slow the system down. Many think I wanted to lower the pressure, but I was annoyed with how fast the system was heating the house, and often overshooting.

Slow and steady wins the race with heating and cooling, every time.

Michaelc

just had my new boiler installed. Found a reputable steam man and the new boiler is 1/3 smaller than either the previous Burnham or the suggested replacement from a bid i got from a different contractor.

I asked the original contractor the question about my current system heating the house too quickly and overshooting. i was told that there was nothing to be done, that was the way that steam worked. glad i found someone with the correct expertise.

MilanD

Am I to understand this correctly: radiators may be oversized for the building heat loss? In this case, size the boiler to building design heat loss, heat slowly and steadily, and don't worry about all rads getting hot all the way across. Right? And as @ChrisJ points out - heat slowly to avoid swings. And how exactly you do that without using some kind of anticipation or Mark's EcoSteam?

To answer that question, and to add one thing to ponder, at least for the gas fired boilers - over which I spent many months thinking due to my particular situation with zoning and overall quest for efficiency: unless some kind of heat loss anticipation system like Mark's EcoSteam is to be used, everyone should also look into installing a 2 stage gas valves.

With good main and rad venting (on a balanced system), this would allow for even lower overall op pressures for the system operations, and would, for all practical purposes, allow you to shut-off radiators to rooms you don't use if so desired, without really oversizing the boiler by doing so. With 2 stage, once the op press for low-fire is reached, boiler will dial down the BTU input. This will slow down the rate at which building temp swings AND also save in fuel while increasing comfort. When the system goes high-low-high-low, it mimics the old coal fire for which most of these systems were designed to begin with. It can be then dialed in for optimum performance by setting the low burs stage to higher or lower overall op pressure to trigger low burn, or by playing with the low stage input pressure on the valve in order to more closely dial in the low stage for slow btu adding to the space heated, equaling heat loss on an average outdoor cold temp for the location.

My 2 cents...

MilanD

Wow.. @Hatterasguy, without reading your link I came to a similar conclusion. My question is though, what controller is used to anticipate and fire the boiler on simmer for a long time? Can't be done on tstat alone, or maybe it can!

The Honeywell TH8320WF tstat I observed for a first time today cycle the boiler while the display temp stood at 69, and then 71. Time it took between 2 firings at 69 was 90 min with nice 2 staging when one of my zones (discussed prior) closed the total 1975 edr boiler and dropped to about 1475 and ran a nice 23 min cycle.

After I had the pm bump feom 69 to 71F (oitdoor temp 37F), now with the zone open and all but 2 rads calling (have a leak somewhere so this riser is off line), we got from 69 to 71 there in about 63 min. Although I didn't observe the whole cycle, I did see low stage engage and tstat cut the burners out 2 min before tstat showed 71. For a moment there I thought the boiler quit working...

After we got to 71, boiler was off for 110 min before firing again to maintain 71F in the building. Outside temp was at 35-37 range, 1-2 mph westerly wind... Old bldng, all original windows but the 5 bigger ones on 2nd floor (2 outside walls in each space), brick, no insulation.

The only thing I can think of, without using the tekmar or ecosteam, is to lower the op pressure to 4-5 oz, and 2nd stage low burn between 1 and 5 oz... Wow. I'll try this tomorrow!

And again, @Hatterasguy, you did it!

Abracadabra

maybe a modulating thermostat.. of course most boilers would need revamping of all the gas train to accommodate modulation.

MilanD

@Abracadabra, see my thread here for today's interesting findings...

http://forum.heatinghelp.com/discussion/160968/2-staging-lgb-7-for-those-who-are-looking-for-more-info#latest