Steam Heating Conundrum of High-Rise Buildings in the US
Igor Zhadanovsky, Applied Engineering Consulting, Newton, MA, USA
Victor Zelmanovich and George Bilenko, Intech21, NYC, USA
Corresponding author: Igor Zhadanovsky
ABSTRACT: Steam/vacuum heating systems are employed in thousands of old tall buildings and even relatively new ones. Although considered obsolete, these systems excels any other in simplicity and resilience and can match modern efficiency standards after thorough retrofit. Efficient and simple, the NextGen vacuum heating is suggested for existing steam heating systems retrofit and for new installations that use modern technologies and materials.
The elephant swept under the rug – steam heating in the US. Swept under the rug is an idiom used for something that has been hidden from the view of others due to embarrassment … You have all the dirt, but too lazy or lacking in time to find something to pick it up, so you lift the corner of the rug and sweep it under.
Till 1930 all skyscrapers were built in North America/US (191/188) [The Skyscraper Center]. Typical office towers and high-rise residential and hotel buildings were not higher than 150 meters [Pietrzak .J, 2014]. They were heated by steam systems, - the most convenient way to deliver heat to upper floors. Reliable hot water circulators were introduced in 1929, and quickly gained popularity because the cost of heating system installation was reduced drastically.
Today’s consensus on HVAC with the highest efficiency for tall buildings is a “ground source heat pump (HP) combined with hydronic piping, and smaller water source heat pumps for each building zone. One kilogram of water can carry over four times more heat than one kilogram of air, while being pumpable and using over 800 times less space. This makes water an ideal heat transfer medium for tall construction” [Tobias M., 2019].
Apparently, enthusiasm for heat pumps obscures the fact that the best heat transfer media is steam, not water. 1 pound of condensed steam carries more heat than 25 pounds of hot water cooled in radiators by 40oF, no pumping is required. Additionally, in tall buildings every 20th floor of precious space is lost for hot water pumps, which is a huge budget sacrifice. The choice of a HP is also questionable because HP efficiency drops sharply at low outside temperatures, meaning the backup system is required when heating is needed the most. Backup system is either an electrical resistance or Power Plant. HP requires 24/7/365 electricity which is produced from oil or gas at maximum theoretical efficiency of 35%. To circumvent such losses, free “green” electricity from solar and wind is asserted as todays "holy grail" to power HP.
In real life, the iconic “green” program in Germany upsurge electricity cost and was finally exposed as a catastrophic failure [Hamlin L., 2019]. Still the public is mesmerized by futuristic ideas. “The growth of wind and solar power offer the opportunity to reduce the cost of electricity, and certainly reduce the amount of emissions. However, this only accounts for about 3% of the total U.S. energy use or about 9% of electric generation energy. In addition, electric generation from wind is often at the wrong time of the day. While there are many ways of solving these problems, solutions will not be easy or inexpensive. Even if there is a conversion to more electric generation from wind and solar, steam will still be the best means of converting electricity to a useful energy source for heating and process work. It simply means that the boiler will use electricity for its energy source. The flexibility offered by steam and steam generation from boilers will continue to keep the use of steam in our foreseeable future”. [Tompkins G., 2020]. Heat and power cogeneration (CHP) efficiency is up to 75% and 24/7 reliability, which makes it an attractive option for new large/tall buildings and campuses.
Pragmatism prevailed over wishful thinking, - according to 2010 reports in NYC “the tradition of steam heat is so strong that even relatively new buildings have been found to be designed and built with steam heating systems” [Shapiro I., 2010]. “28 newly constructed properties, totaling over 7.5M SF of building area, installed some form of steam heat between 2000 and 2010. Most buildings above 50,000 square feet still use steam-based space heating. 72.9% of buildings have steam boilers fired by natural gas or fuel oil, while 10% rely on Con Edison’s district steam service. In other words, 81.9% of heating systems in large NYC buildings still use steam [Urban Green Council, 2019]]. The propensity/partiality toward steam heating in large buildings is typical of big cities in the US and in Europe as well [Gallo E., 2005].
Solutions already tested, found inefficient but still employed.
The inborn drawback of steam heating is uneven heat distribution. Steam of 2 psi pressure (safety limit) has to push air through multiple air vents every heating cycle in order to get simultaneously into each radiator hundreds feet away. That's why ¨Dead Men¨ meticulously equilibrate boiler capacity, pipes and radiators sizes, pressure drop and heat load for each installation. As of today, efficiency and comfort in the majority of these systems is ruined due to poor maintenance and reckless modifications. It’s a reason why steam heated buildings are typically pictured with open windows. Methods to overcome the problem are as follows:
Balancing using air vents [PARR 2011, Choi J., & Ludwig P.2012], orifices (Oland C.B., 2001) and Temperature Regulating Valve (TRV) [Bobker M., 1995] is time, money and labor intense, resulted a modest 10-14% fuel savings or no savings at all, but still widely employed to supplement building envelope and lighting upgrade.
“Smart’ radiator cover” [Radiator Lab, 2014] addresses room overheating rather than the whole heat distribution problem, another disadvantage is switching from radiation to convection heating by air which causes a significant decrease in efficiency and comfort.
VRF air conditioning is today’s popular type of HP in which one outdoor unit can be connected to multiple indoor units. Each indoor unit is individually controllable by its user and a variety of unit styles can be mixed and matched to suit individual tenant requirements (e.g. high wall units, cassettes, and ducted units). Recent study concluded that buildings most suitable for MSHP (Multi Split Heat Pump) retrofits are those with high-cost heating fuel such as liquefied petroleum gas (propane), fuel oil and, especially, electric resistance. Buildings with natural gas service are less suitable. Converting from electric resistance to MSHPs saves approximately 30% of annualized energy- related. Converting from oil saved about 4%. Converting from natural gas would cost about 30% more. In the Boston climate, converting from electric resistance to MSHPs is projected to save approximately 50% of annualized energy-related costs. Converting from oil saves about 3%. Converting from natural gas would cost 24% more. VRFs are suitable as primary heat sources in new well insulated construction. ” [Dentz J., 2014]. In old buildings (and most steam heated buildings are 50+ years old) a backup heating system is a must to have.
Today's best solution
Steam heating conversion into hot water heating (HWH) is considered the best approach for today. The take-away from the 2010 successful steam to HWH retrofit project on a twelve story building at 179 Henry str., NYC were summarized as follows: “Over the years, many of us in the New York City multifamily energy efficiency world have talked about how cool it would be to convert steam-heated buildings to hydronic heating. The problem is not one of will but one of money. Changing the boiler is not the big deal—it’s the heating distribution system that is the challenge. … Plenty of these conversions have been done in the last 20 years in buildings that were gut rehabs. These jobs did not always get the best boilers, or insulation in the walls, but they did get a more efficient heating distribution. The real challenge was to convert a building with steam heat, with tenants in place “[Rieber D., 2012]. The project required boiler replacement, core drilling the concrete deck floors (12 in all), running and enclosing the new piping and the heating elements. Fuel savings were 33%.
Examples of successful steam heating
The efficiency of a thoughtfully retrofitted steam heating system can match today’s standards:
- The 16-story 1893 Monadnock Building (Chicago) manages a top Energy Star score of 98 in spite of its age. … the brick skyscraper has cut electricity and gas consumption by about 33% by weather stripping, improved steam system automation, and the gradual installation of sensor controlled lighting [Tobias M., 2020]
- The14-story historic Joseph Vance Building (Seattle) constructed in 1929 and retrofitted in 2006. For economic reasons, the project did not replace the existing steam heating system, but recalibrated it instead. In 2009, the U.S. Green Building Council (USGBC) awarded the Vance Building LEED for Existing Buildings (EB) Gold certification. The building also achieved an Energy Star rating of 98 (out of 100). [Kheir Al-Kodmany, 2014 ]
Besides efficiency, superior comfort can be achieved by steam heating systems even in very old buildings (1850th), - US presidents and their spouses in White House and financial advisors in the US Treasury buildings would not accept anything but the best [DOE 1999, Christopher D. 2013 ]. Treasury building received a LEED Gold certification in 2011 [Tangherlini D., 2011]. These are not tall buildings, but the technology is the same.
- There are multiple cases of worn out steam heating system successfully replaced by HWH resulting in a savings ranging up to 40% (usually complementary to a building envelope and windows improvements)
- Many times old steam heating system demonstrated superior comfort and savings in a range of 30-50% thanks to knowledgeable maintenances and tune up
- It’s strange, in almost 100 years since the HWH introduction there was no single study of steam heating direct comparison to HWH. There is, though, accidental evidence of similar fuel usage in identical buildings with HWH and well-maintained steam heating.
Public fondness toward HWH is constantly fueled by complaints about noise and low efficiency of the steam heating system which continued functioning even after decades of neglect and scarce maintenance. Maybe it’s more rational to find a way to optimize steam heating systems performance rather than get bogged down with expensive conversions?
Evolved solution – NextGen vacuum heating
Vacuum heating, - another kind of steam heating, - was very popular in the 1910th and actually preceded heat pipes concept. Heat Pipe (please, don’t mistake it with Heat Pumps) – is the most efficient, resilient, and electricity independent method of heat transfer, employed in NASA spaceships since the 1970th. Basically, it’s a closed ends tube under vacuum where working liquid evaporates at one end and releases latent vaporization heat by condensing at the other end.
According to the 100 years old data on steam heating conversions into vacuum heating, reported fuel savings were 30-35% [Holohan D., 2004]. Instead of pushing air from the system by steam at 2 psi, steam is pulled from the boiler by 10-25”Hg (5-12.5 psi) vacuum at speed of up to 150 mph, which ensures quick and even heat delivery to the farthest radiators in the system. Additionally, thanks to the naturally induced vacuum in the idle cooling down system more heat is sucked up from the boiler after the heating cycle, which would otherwise be lost in the steam systems. At the same time corrosion is reduced because of limited oxygen access into the system. On top of this, steam temperature can be regulated by the vacuum level in the system, so soft comfortable heat can be delivered in warmer weather, rather than being fixed to the 214-218oF range found in steam systems. A good example is the 80+ years old vacuum heating system in the iconic LEED Gold Empire State Building (ESB). In the 2009 retrofit, instead of replacing the old vacuum system by hydronic, it was successfully restored to the original design.
The vacuum return systems were widely used to speed up a cold start of steam system heating typically in large and tall buildings. The technology was so conventional that the sale of more than 60,000 vacuum pumps was reported from a single leading supplier since 1921, with most (about 50,000) purchased prior to 1980 [Clark L., 2003]. Most of these abundant systems are still around waiting for upgrade/retrofit.
Unlike Heat Pipes, today’s vacuum heating is actually a “pseudo” vacuum; the vacuum section of the system is separated from the section under steam pressure by a steam trap behind each radiator(s). These required steam traps present an ongoing maintenance problem. Steam traps on radiators last only 10 years at best, and are often ignored when they fail because of the expense and annoyance of repair. Steam leaking through a single failed trap (out of hundreds in tall buildings, - 6600 in ESB) overloads the vacuum pump, condensate pump, etc. The result is unbalanced, noisy, and very expensive systems. Compared to many other vacuum systems that gave up after a multi-year struggle, ESB definitely excels in steam traps preventive maintenance.
For existing steam/vacuum systems steam traps, this problem can be resolved by converting existing steam/vacuum heating into NextGen vacuum heating system. Observation of vapor and condensate flowing through the transparent plastic piping in the vacuum heating system revealed surprising insights. It turned out, the vacuum system can self-balance quickly and evenly with proper system design [Holohan D., 2015]. The trick is to prevent steam “short passing” toward the vacuum pump. This has inspired a new “steam traps free”, entirely under the vacuum system paradigm. NGRID study [NGRID 2014] confirmed energy savings of 25-35% for retrofitted old steam heating systems and up to 50% for complete replacement. The study was carried out on a small scale project but steam/vacuum systems are easy to scale.
Steam heating systems in tall buildings are either 2-pipe steam or 2-pipe vacuum heating systems. Without any contempt for the great planning and implementation of the 179 Henry street. NYC project, imagine now that the same building was converted into new vacuum heating system:
- Old boilers, piping and radiators can be salvaged/upgraded/fixed/repaired after a leak tests, steam traps are either left in place or removed
- The only new equipment is a vacuum pump, steam/condensate separator (existing vacuum pump and separator can be employed), sensors and controllers
- The only new piping is the vacuum line on the second-to-last floor ceiling and connecting return lines to the vacuum pump (located either in the basement, on the roof, or designated room on the top floor).
- Plumbing and radiators may be upgraded later on when the building will go into gut rehab.
- Estimated fuel savings - 30-35% according to 100 years old data on steam heating conversions into vacuum heating [Holohan D., 2004]
This is a minor job compared to the complete replacement of existing steam boilers, piping and radiators by hydronic, on the top of adding mechanical floors (for skyscrapers higher than 20 floors), circulators, PRVs, etc.; not to mention the disturbance of tenants, - the main reason why most retrofits are indefinitely postponed.
For the systems with old piping, the majority of leaks are at supply valves near the radiators and can be fixed. In our experience with three retrofits of residential systems (all are 100+ years old steam heating) no major leak was found in the pipes. Minor leaks from hidden inner-wall piping are inevitable, but the problem can be resolved by converting the steam system into a “vacuum boost” heating system. Here, steam quickly and evenly fills the system under vacuum, raises the pressure to 1-2 psi (to avoid air leakage into the system) and continues to heat the building at low positive pressure till the thermostat is satisfied. Retrofit into “vacuum boost” technology does not require frustrating efforts of leak detection and repair. For “cold” vacuum sustaining test a drop from 20 to 5”Hg in 2 hours is acceptable, compared to a 20-18” Hg drop in 2 hours required by the Vary-Vac – the most popular today’s vacuum heating system.
Compared to HWH, leaks in a vacuum heating system are much less of a problem - no water flooding to the lower floors and expensive repairs. The only moving part in the NextGen Vacuum heating system, - vacuum pump –is never exposed to steam and is employed in 5-10 minutes intervals for 1-1.5 hours daily. With a 5-10 thousand hours warranty time and average of 4 month winter season, life expectancy is in a 37-75 years range until the first needed repair/replacement. Condensate is returned into the boiler by gravity; in case of district steam, by a designated pump.
Modern technologies prospects for vacuum heating systems in tall buildings
All existing steam/vacuum heating systems employ heavy steel piping. ESB plumbing contains 50 miles of radiator pipes, including 24” risers, and 7000 cast iron radiators. Soldered copper tubing was restricted from steam/vacuum heating because rapid heating caused cracks in the soldered joints. Modern ProPress plumbing method employs no soldering, slash installation time and is backed by a 50-year warranty against rust, defects in material and workmanship. Furthermore, the piping diameter/weight is reduced drastically; also reduced is heat loss, the amount of condensate in pipes, and heating time compared to steel piping. In the NGRID study, the 2 ½” steel pipe at the steam boiler exit was replaced by a ¾” copper tube – this resulted in an 11.5 fold drop in price and 16 fold drop in weight (please note this also corresponds to a 16 fold drop in the system preheating time and condensate amount).
Another plumbing option is thermoplastic piping, - no rust, easily glued, quickly assembled, and leak-proof. An Aquatherm polypropylene piping system operates at temperatures up to 200oF (93oC) at 15 - 100 psig (1- 6.8 atm), so technically it should handle saturated water vapor at 6”Hg/200oF (93oC) without any problem. Like Propress, Aquatherm is backed by a 50 year warranty, and available at larger diameters (up to 300-600mm). Polysulfone thermoplastic is already approved for low pressure steam systems in the US – up to 230oF at 15psig, it can be welded, sawed, and glued like PVC plumbing.
Clamped silicone/rubber fittings can be utilized for plastic piping; additional benefits include easy assembly/disassembly/repairs/adjustment, compensation for thermal expansion/contraction, and noise reduction. A polysulfone tube with clamped silicon fittings worked in a tested vacuum heating system for 3 winters without any problem. Liquid Crystal Polymers (LCP) with heat deflection temperature of 290C can be utilized at higher temperatures.
Modern methods of leak detection allow annual proactive testing to find new leaks and keep the system operational for many years. Needless to say, thermoplastic piping with no rust/oxidation problems is of low maintenance and easy to repair.
Cast aluminum radiators
In steam heating systems pipes accounted for 30-35% of the total system weight and have to be reheated to 214oF every heating cycle. To reduce the heat loss of pipe reheating, heavy radiators are employed to accumulate heat. This archetype can be dismissed if much lighter copper or polymer piping is utilized.
Modern cast aluminum radiators present a much less expensive, lightweight alternative, they are slim, modern looking, have a modular design (length adjustable) and warrantied for up to 20 years at a pressure 7 bar. Such radiators by SIRA have been working problem free in a tested vacuum heating system since 2015 [Zhadanovsky I., 2017].
New control paradigm
Presently, vacuum heating systems control heat distribution via control valves on the supply lines. These are expensive items because of steam rating and large pipes diameters. Instead, the new technology employs control valves on smaller diameters vacuum lines in order to direct steam into the required system partitions. Normally open valves close when the vacuum line temperature rises above 30-40oC and are never exposed to hot vapor so a long life span is expected. Closed valves prevent air removal from a particular radiator(s), and therefore result in only partial heating (similar to TRV operation). Heat distribution and a sequence of heat supply into system partitions can be dynamically controlled.
Intech21 implements modern algorithms of heat distribution control in a group of buildings (or stand-alone buildings) and wireless sensors and controls. The novel algorithm is based on the building heat loss which is calculated using the apartment’s indoor, outdoor air and condensate return temperatures. The approach alone saved 25% in heating cost in the Castle Hill project, -14 steam heated 20 floor high buildings [NYCHA 2014], - and can be readily integrated with NexGen vacuum heating.
Instead of radiators, air handlers on every floor and heat exchangers for distributed hydronic subsystems can be employed in new installations. Compared to hydronic only system, a significant size reduction of air handlers and heat exchangers can be achieved due to higher steam specific heat capacity, linear velocity and better heat transfer. Vacuum heating system plumbing for such “hybrid” systems would be simplified and heat distribution would be controlled easier. An additional benefit would be the possibility of per floor/apartment heat consumption metering in distributed subsystems, which is problematic in steam/vacuum systems.
CHP benefits and geothermal outlook
Steam/vacuum heating can be readily integrated into CHP, the most reliable and efficient electricity and heat source. In high efficiency power plants, a steam turbine exit is connected to a condenser to extract maximum electricity. The vacuum in a condenser is created via steam condensation by cold water. If the building vacuum system is connected instead of a condenser, this additional electricity would be received without steam and cold water expenditures, cooling tower, pumps, etc. In summer time, any excess steam of high temperature can be utilized in an adsorption cooler on the roof (more efficiently than hot water). Again, no electricity wasted on pumping water.
Steam is a by-product of untapped green technology - geothermal heat. “2000 times US annual energy use could be supplied indefinitely 24/7 using existing Engineered Geothermal Systems (EGS) and perhaps 10 times as much with improved technology” [Chandler D., 2010]. At 5.5 km depth, 175-225oC heat source can be reached on the most of the US west part, and 100-150oC on the east part. A mature EGS can supply enough electricity for 800 to 41,000 average U.S. homes or dozens high-risers. The $5-10M cost of drilling (4 and 6 km deep well, correspondingly) [Tester J., 2015] is not an outrageous expense for reliable heat and power source compared to $7-20M average floor price tag for high-rise in Chicago and NYC [Barr J., 2019], At 500% efficiency [Egg J, 2015] this opportunity dwarfs the promises and attractiveness of HP, wind and solar power.
The US is not alone in dealing with steam heating upgrades, steam is also widespread in Europe [Gallo E., 2005] and China [Xia J., 2009]. Worldwide there are thousands of steam heated buildings, including high-risers, which would benefit from a simple, efficient and reasonably inexpensive conversion into vacuum heating. Modern plumbing technology and materials makes vacuum heating a very attractive choice for new installations as well.
It’s not unusual that old technology gets a second chance thanks to the progress in knowledge and materials. In 1893 electric cars lost the Paris-Rouen race and they have made a magnificent comeback since then. Who is to say that won’t happen to vacuum heating technology for new buildings, especially skyscrapers?
The research on NextGen vacuum heating was inspired by Dan Holohan books and advice, supported by Kith Miller of NGRID and Ed Infantino of A&M SERVICES.
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