Efficiency options for 2-pipe, downfeed, vacuum

Therm_lag

In 1979 the first condo board meeting entertained motion for an energy audit of the 24 story ‘20s two-pipe steam heated building.  The <strong>energy audit</strong> is now in progress, and I invite comments on options for more efficient steam distribution.  I define <strong>distribution efficiency</strong> as putting the right amount of steam to the right location at the right time (or replace “right amount of steam” with “acceptable comfort temperature”).   

<strong>The boiler</strong> is a 20 year old three-pass fire tube with 83% thermal efficiency.  The vacuum type distribution is downfeed with supply loop in roof crawl and “risers” connected at a crawl below first floor. 

<strong>Overheating</strong> as low as 16th floor leads residents to keep most radiators shut off.  We will survey the building to learn about windows kept open to control temperature.  We will also inquire whether HeatTimer boiler control is set longer to maintain comfort at lower apartments.  More heat can make imbalance worse if it leads residents to open windows at top.  The neutral plane for stack air leakage moves upward and  air entering lower apartments is driven in at higher pressure.

<strong>Other details:</strong> four large apts per floor, separate DHW system, no ventilation, window replacement by individual unit owners (about 50% after 20 years), top and bottom crawl spaces are quite air tight and stack air flow appears to be primarily from boiler room combustion air supply to space around boiler stack that runs through building. 

<strong>Balancing comfort conditions may require both air leak reduction and control of steam delivery</strong>. Our current assumption:  overheated residents open  windows, and it is unrealistic to expect this mode of stack air movement to stop unless steam supply to the lower apartments increases relative to top floors.



<strong>Here are some ideas</strong> about increasing steam supply to lower apartments.  I invite  constructive response, pot-shots, what-have-you. 

a)     The <strong>vacuum pum</strong>p runs continuously throughout heating season.  We plan to check vacuum to assure that lack of vacuum causes poor steam distribution to lower floors.



b) <strong>Convert downfeed to upfeed</strong>.   Assumi9ng adequate riser pipe size, this would require upsizing pipe at lower crawl space,  changing pitch of pipes at upper crawl space, and boiler area piping changes including shifting the vacuum equipment to former riser.



c)  <strong>Insulate steam piping</strong> from the top moving down, to limit that amount of heat provided by piping in overheated zone.  Piping within view has corrugated paper  insulation mostly in place. Risers are enclosed at sides of perimeter columns and this enclosure could be filled with insulation.



d)     <strong>Upgrade capacity of riser base vents</strong> to let steam fill risers before entering  radiators. I suppose this is the usual fill pattern for vacuum systems though I don’t know this detail.



e)     <strong>Fit radiators with orifices</strong> at entry side and place thermostatic radiator valves at  rooms that overheat, perhaps most of radiators at top of building.  Vary system pressure on outdoor temperature. 



f)    Place <strong>TRVs</strong> on all radiators. 



g)  <strong>Quarter-turn manual (ball) valve</strong>s to allow resident to easily activate or deactivate radiators.



<strong>Are there better options than the above?</strong>  I see posts and threads on many of the above options, and hope to bring some focus to these with this thread.



It’s great to share knowledge and opinions about reducing energy use.  It would also be great to have <strong>careful documentation of energy efficiency upgrades</strong> for a particular retrofit strategy applied to a particular system, like down-feed 2-pipe steam with vacuum.  With thorough study, improvements that work can be knowledgeably applied to particular types of systems.



The best retrofit strategy will balancing steam supply in relation to <strong>differences in loads</strong> among apartments:  external loads (solar, wind), and internal loads (e.g., cooking).   I’ll follow with some options, one of which may work better with a  particular “vertical balancing” option above.

Rod

2 Pipe Downfeed

Hi- Where are you located?

- Rod

jpf321

where and ....

where are you?



you've got the right solutions in some of your options .. being able to visit the site and have a closer look would be helpful.. NYC area? if not, post copious pics of your boiler and building piping, including returns system, false-water line if any, traps, vents, etc.



you're on the right track. the key is to reduce/shed the load where/when isn't needed.. which combinations of your many options auto-magically provide these characteristics? besides the point that no steam pipe should never be un-insulated. i assume that there are Rad-Traps at each rad and I also assume every trap is broken (or at the very least, that you should never perform trap maintenance again HINT HINT)

Jamie Hall

This is a big enough job

that you should at least consider, depending on where you are, getting one of the really top notch steam men (e.g. Gerry Gill, Steamhead, etc.) on this site to come and consult for you.



That said, a few more or less obvious responses...



Venting.  The "risers" (downcomers) need to be vented heavily at their ends -- the bottoms.  The objective here is to get the steam distribution as even as possible over the height of the downcomer.  It is possible that your vacuum system has enough oomph to do this.  It is also quite possible that it doesn't.



Control.  My first thought on reading through your post is "TRVs!".  On a large system like this, they -- or some other means of local control -- are almost mandatory.



Pressure.  There should be no need to alter the pressure at which the system operates.  Cycle time, yes; that will vary with both outside air temperature and system demand.  But pressure, no.  2 psi is ample -- and may be more than you need.



Stack effect.  Is there a way to separate the apartment air effectively from the stack and stairwells?  Or does the required air change for air quality considerations depend on this?  If it is the latter, I would certainly want the stack to always be at a negative pressure relative to the apartments, and would want the air flow from the apartments into the stack to be under very good control -- which is tricky.



I may have some further thoughts...

Therm_lag

Metered utility use may reveal unbalanced heating

Attached file is graph of metered gas use for building with 2-pipe downfeed vaccum.  Pattern of utility use can reveal efficiency opportunities.  There are several interpretations for fuel use to flatten for billing periods at low temperatures, including inadequate boiler capacity.  Based on information to-date the audit will seek to document imbalance.  At the same time, we will seek to rule out steam imbalance causing higher rate of consumption during milder weather.  This approach lets us become more certain what we're trying to correct, and the process usually lends some detail that marching forward with an assumption, however reasonable the assumption, might obscure.   

jpf321

looks like a job for

boilerpro! chicago design temp used in the pdf

Therm_lag

Balancing system in relation to differences in loads among apartments

Several strategies are available to balance steam supply in relation to steam supplied from top of building down, and to compensate for stack leakage that tends, like steam supply, to overheat the top of this building and underheat the bottom, listed at top of thread (Nov  5 “Efficiency options for 2-pipe, downfeed, vacuum”).



The following strategies also have to do with steam supply and control and address imbalance beyond downfeed steam supply and stack leakage.



I'm interested in a strategy to vary steam supply in relation to external loads that vary by orientation.  Sticking with the definition of efficient distribution, we’d like to limit steam supply to zones that are less impacted by steady winds from one direction. Northwest winds prevailing in Chicago will increase heating requirements

at these orientations.  A difference in heating requirement will evidence as temperatures dropping below the comfort range in apartments facing the wind.  

Let's say a “cold spot” thermostat is placed where zone conditions may first drop below comfort conditions.  The thermostat sets boiler to higher heat output, adjusting the outdoor reset to reflect that wind influences the setting that is based on outdoor temperature.  Automatic  control could increase the setting for boiler temperature, pressure, or cycle length.  Apartments not exposed to wind load would perhaps overheat, though the zone with load would be controlled to not exceed comfort temperature in response to additional heat loss, limiting heating of the selected zone and avoiding unnecessary temperature increase elsewhere.   I'm  interested to hear experience or comments on prevent overheating with the following or other methods.



1)   Close main air vents at risers  serving orientations that are within comfort temperatures.

2)    Close suction from vacuum pump at risers  serving orientations that are within comfort temperatures.

3)    Install sufficient TRVs to prevent overheating in zones that receive additional steam supply; enough TRVs to keep the orientation experiencing additional load at comfort temperature.



Steady wind loads from one direction might be addressed by “1)”

or “2)”  above, though differences in winter (and fall and spring) solar loads on east and south orientations of this building are likely greater than wind. Solar loads vary by height in addition to orientation due to shading by neighboring buildings which are similar to this building’s 24 stories.  The “cold spot” thermostat needs to be located near base of building to detect need for additional heat at apartments below the “shadow line” of neighboring buildings.  The height of the shadow line will change

substantially from milder months to the coldest month of the heating season, making the selection of two zones (above/below shadow line) on the sunlit orientations of the building a problem.  Splitting

steam supply pipe into upfeed and downfeed lengths (variation on option “b)” above) might provide zoning for solar heated and shadowed apartments, though the control complexity and cost of piping work seem to rule this out. 



Variation of internal loads in apartments may cause overheating.  We do not have data on extent and time of internal load variation in apartments, however it seems reasonable to assume there is no useful pattern that would lend to zoning beyond individual apartments.  Internal loads that frequently cause overheating can be addressed by TRVs, especially targeting the room(s) where internal heat originates (e.g., kitchen).  Apartments experiencing overheating once other balancing measures are in place can be individually addressed with a manual shut-off (for infrequent overheating) or TRV (see “f)” and “g)” options above).  



We will try modeling the building using TREAT energy analysis software with central boiler and uniform steam supply and then with zones and steam supply set to temperatures in zones to get a sense of the savings potential of a zone control strategy.  Zones will isolate each orientation, and further divide shaded orientations into a zone with portion of windows shaded, and separate zone with windows unshaded.

Therm_lag

Experts are essential

I believe all energy auditors should seek information from firms that provide installation.  I "walked" this job with BoilerPro a couple of months before the condo selected an audit firm.  Several crucial observations were made at that time.  The client requires an independent report before accepting a course of action, and this report will include observations properly acknowledged and a recommendation to work with an experienced firm. 

jpf321

TREAT Software ...

Wow .. I went to school in Ithaca (CU, not IC) , where the TREAT software originates .. and I have to say Brindley St is not somewhere I'd ever heard of (and I ran with both Fire and EMS) .. but I used to work for a bar right near there .. Max's .. ah the good old days!

nicholas bonham-carter

vacuum system problems

this sounds as though the steam is not arriving at all parts of the building simultaneously. probably air is in the way.

what is the vacuum maintained in the returns?

what  pressure in ounces is the cutout set to?

by the time you have written up all these descriptions, half the occupants will be desiccated, and the other half frozen!

i would try lowering the pressure, and finding out where the steam stops in the system., and why the air is preventing it. i am sure that there is a control problem here as well.--nbc

Dave in QCA

Good Design, but broken

You have a very interesting situation here, and it looks like you have made a good list of observations and also, of possible actions to remedy the problem of terribly uneaven heat in the building.

I think the first assumption that should have been made, and that you have missed, is that the heating system in the building most likely worked when the building was new.  In fact, I would imagine that it not only worked, it probably worked very well.  Obviously, it does not work well now, in fact it sounds like a really terrible living situation for the occupants of the building.

I am going to go through the list of options and observations that you have listed and give you my opinions on them.  Please realize that I may be way off in left field, as I am handicapped by not being able to see the buidling and system with my own eyes.

a.  You note that the vacuum pump runs all the time.  It should not.  I should run to the point of producing a vacuum, and then shut off.  Does it produce a vacuum at all?  How much?  I would suspect that the vacuum pump no longer works, or that the system has become so leaky that it can't hold a vacuum.  Leaky valve stems can be enough to prevent a system from being able to pull a vacuum.  Your system depends on vacuum for the steam to be able to distribute correctly.  It is the means in which the air is vented out.  It should also allow the system to run at a lower temperature than the temperature of steam, which should also help in evening out the heat in the building.



b. Convert to upfeed.  The direction of the feed is NOT the problem.  Downfeed systems were considered an advancement that was able to produce even heat throughout the building.  If you change the piping, but don't fix any other problem, you will have very warm lower floors and freezing upper floors.



c.  1 inch insulation on piping should be sufficient for the piping to work correctly and not lose excessive heat to unheating areas.  Your problem is that the steam is not getting to where it needs to be.  If all the steam piping was getting hot at the same time, its minor loss to the building spaces would be equal and not a problem.  Packing he piping chases with insulation is probably not a good idea.



d.  Getting the risers / drops to vent well is critical.  I would assume that this is supposed to be occuring through the vacuum system, but probably is not.



e.  Orifices may be a good solution.  If you abandoned the vacuum system, corrected the venting for the at the bottom end of every steam drop, orifices could be a solution to equalizing the radiators and assisting in getting the steam to enter all radiators at the same time.  There is a great article by Henry Gifford on this subject.  However, it probably doesn't work well with a vacuum system, and it appears that repair of your system rather than redesign should be considered first.



f.  TRVs on all readiators would certainly help.  The warm areas would automatically close the radiator valves, thus forcing the steam to move on to parts of the buidling  where it is not currently arriving.  This may be a good option even iff the underlying problems are corrected with great results.  The reason is, in my opinion, even if the system is working the way it is supposed to, there are daily differences in weather.  Winds change direction and some days you may have huge solar gain, and on cloudy days, you will not.  TRVs will automatically correct for these changes and will produce a much more controlled heat in the building, therefore, a lot less waste.



g.  Quarter turn ball valves are not a good choice.  If you don't want to spring for the cost of the TRV's, and if the current radiator valves do not work, and are not repairable, then you should install new manual RADIATOR valves, intended for steam use.



Additional ideas.....

Well, first of all, the proper operation and distribution of the steam in this system needs to be corrected and restored to the manner that system would have operated when it was new.   That is the first and most important priority.  If there was not a good system of controls that decided when the boiler should fire, and how long it should fire, etc., then a control system to provide that function would probably be a good investment, but in no means an option to be done instead of making the fundamental repairs to the system that are so obviously needed.  Such control systems as HeatTimer or Tekmar 279 migh work well.



Probably most important, you need to get the services of a steam heating specialist; someone who understands large heating systems and can trouble shoot your system to see what is really going on and why, and also, to determine that manner in which the system was designed to operate, and to provide real solutions to enable the system to operate that way again.   Options for improvement would then be icing on the cake and should be able to help you make your building function as a cost efficient and very comfortable environment in which to live.

Best wishes in this, and please keep us up to date here on the wall.  We love to know the outcomes of these problem cases.

Therm_lag

Thanks, Dave in QCA, Nicholas, others

This is very helpful and will guide "boiling the options down" to those that achieve needed result in a direct simple manner.



I am working with this energy audit client to:

  install gauge on vacuum pump,

  have end of line vents evaluated for upgrade,

  correct insulation defects of 1920's piping (limited areas)

  insulate boiler room piping

  install several TRVs to get the process down pat (most radiators have enclosures)

  install motorized damper control of combustion air (may help separate hot water   boiler having air/fuel mix thrown off).  Dedicated DHW boiler may receive

motorized damper or upgrade to 90+ boiler depending on audit savings estimate

now being performed

  several retrofits to DHW: pipe and tank insulation, pump control



Next steps to study energy use will be

  temperature log to graph steam delivery over several days

  observe vacuum pump performance once gauge is in place

  selective review of steam trap function, and review of maintenance history

  make a number of other observations and tests to get a better picture of

building air leakage, insulation of the enclosure, etc



Energy audit covers central and whole building: heating, DHW, insulation, air leakage, windows, lighting, pumps, ventilation.  Audit will also provide information for residents to reduce energy use in dwellings.  You're aware that heating efficiency options can extend to combustion air supply, burner, heat transfer, boiler operating controls, vent/chimney, comfort controls.  At this point, steam enters the distribution system.  That is, energy audit covers a lot of potential defects and opportunities. 



I believe traps are probably well maintained, however I'm interested in

balancing the building using orifices and discontinuing traps.  It seems

to me that vacuum system should work OK with orifice setting rate of steam to

radiators, especially if lines to radiators are aggressively vented.  You

may have insight on this - I suspect vent system properly and install TRVs

where overheating is persistent and orifices will not be justified, or wait and

see, or maybe they don't make sense to begin with.  I am interested in

having TRVs where needed, though limiting the cost of overall distribution

upgrade by having only the number of TRVs needed.  Many residents now shut

off radiators on their own.  I'm receiving difference of opinion whether

quarter turn valves make sense to let residents more easily control radiators

they already control manually. 

nicholas bonham-carter

most important point to remember

dave has brought up the key point: the system must have worked properly when first installed.heating system comfort, and efficiency are not modern inventions.the condo board must realize that. if the building had those heating problems when new, the installer would have been run out of town [it is chicago isn't it?]

probably, they have had unqualified plumbers in to "tweak" the system for greater performance. this work may have only made things worse. by now there should have been the vacuum and low pressure gauges in place for a week or so, and so what are the results?

instead of waiting until all of the energy audit work is complete, why not suggest the expenditure of a few hundred dollars to cure the most obvious defects and get it back to "stock" [low pressure, and functioning vacuum system].--nbc

more thoughts after my 3rd cup of tea!

does the connected radiation match the capacity of the present boiler, and if not, can it be fitted with a hi-lo-hi burner?

this would be an excellent use of your IR camera, to show how the steam travels through the supply piping. maybe some of the boiler piping is incorrect, and steam is wrongly forced into some parts of the building first, rather than "arriving" at all places simultaneously.

to recap our collective advice here, get the system functioning as it once did when first installed. then it can be fine-tuned to offer greater efficiency, including any upgrades to the building envelope.