[A] few years ago (1895) a heating engineer made use of the plumbing repair parts following
expression in discussing the future of the heating business before a
If you can circulate a system below atmosphere in a large building
you can certainly circulate it below atmosphere in a dwelling house.
If you can circulate it below, how much below can you circulate it?
It is possible that in a few years from now we will be heating
houses not by hot water but by steam below atmospheric pressure,
of such a low temperature that it gives all of the advantages
of hot water without any of its disadvantages.
The first steam heating systems where installed in the 1840s and
quickly became popular. In 1855, steam heating was installed in the
White House and because of the building's importance, this system
always received good plumbing pipe repair care and knowledgeable maintenance. The latest news
regarding the White House steam heating system came in 2001, when the
system passed a rigorous energy audit by the DOE (2001). It's
doubtful that any modern heating system would survive as long a period
of service. As a rule though, most steam heating systems do not receive
the proper attention and serve for a shorter amount of time before
The basic single-pipe system (SPS) setup is shown in Figure 1.
Water (as a liquid) heated in a boiler becomes steam (a gas), which then
rises through the pipes and condenses in plumbing problems radiators, giving off latent
heat. Radiators become hot and heat objects in the room directly, as
well as the surrounding air. Steam and condensate flow in opposite
directions in some parts of an SPS, so low linear velocities are
required in order to avoid water hammering. Steel piping of large
diameters is employed to reduce linear velocities.
For every heating cycle,
* pipes are heated to steam temperature in order to get steam into
* air is pushed from radiators through vent valves and sucked in
when the system is cooled.
[FIGURE 1 OMITTED]
This system has no moving parts except for the air vents, operates
at a low pressure of 1-2 psi, does not need electricity if steam is
supplied by a gas boiler with how much does a plumber cost self-generating controls, and if it is
shut down in winter there is much less danger of freezing.
In 1885, the first two-pipe system (TPS) that did not need air
vents on the radiators was patented by Frederic Tudor of Boston (Pierce
1922). In this system, a separate line returned air and condensate back
to the boiler room. Such an arrangement enables control of steam
distribution by valves on the steam supply line, but the additional
piping made installation more expensive. Some systems built to Mr.
Tudor's original design are still operating today.
Forced-air systems' entry into the U.S. market shattered the
dominance of steam (and hot water) heating. The superior quality and
efficiency of radiant heat was sacrificed for convection heating, all
for the sake of a lower installation cost. Very few steam heating
systems have been installed in the last fifty years.
Today, steam heating systems share some common problems:
* A majority of the systems are old,
* Asbestos insulation has been removed and not replaced with a
* Copper tubing was not utilized because soldered joints cracked
when rapidly heated by steam,
* Large-diameter steel pipes were employed that caused high heat
loss and long heating time, especially if not insulated, along with high
installation and repair costs.
* Heavy radiators are slow to heat up, and they continue to emit
heat long after the setpoint is achieved.
* Aging systems develop noise_
* Poor temperature control and uneven heat distribution through the
building exist; for example, lower floors are overheated and upper
floors are under heated.
* Not all contractors are familiar with steam; repairs,
maintenance, and changes are often made without experience and technical
expertise, and this causes poor performance.
Still, one-third of all Americans live in the Northeastern states
(CT, ME, MA, NH, RI, VT, NJ, NY, and PA) where the core heating systems
are 50- to 100-year-old steam systems (Secor 2007). A significant number
of old government and public buildings are steam heated as well. There
are more than 30,000 district heating systems in United States cities
and on university and colleges campuses; many of them still using steam,
and there are thousands more abroad (University of Rochester 2011).
CHALLENGES FOR STEAM SYSTEMS RETROFITS
Building retrofits are one of the largest energy-saving
opportunities today. In many old buildings, steam systems are normally
being converted into hot-water heating systems. A major challenge in the
conversion from steam to hot water is the pressure increase from 2-3 psi
up to as much as 30 psi in residential systems and more on some
commercial jobs. It's no wonder that an old system's
components start leaking when converted and need costly
repairs/replacements. Extra investments include new water pumps,
expansion systems, additional piping for SPS, zone controls, valves,
differential pressure control valves, bypasses, etc.
Data for the conversion of steam heating systems into hot-water
systems collected by the Minnesota Center for Energy and Environment are
presented in Table 1. Based on the price fluctuations (DOL 2011; DOE
2011), estimations were made for the payback period in 2010. On average,
converting to hot water is said to provide 27% fuel savings for TPS and
19% for SPS. These improvements should be attributed mostly to the
replacement of boilers that are over fifty years old, rather than to the
enhancement of the system's performance. Without a boiler upgrade,
anticipated fuel savings should be less for the conversion into hot
water (situation for steam district heating systems or steam systems
equipped by efficient boiler). Also, this study does not discuss the
condition of the existing steam systems and the payback potential from
simply repairing and optimizing rather than converting them.
Table 1. Multifamily Buildings Heating Systems Conversion from
Steam to Hot Water (Lobenstein and Hewett 1995)
1995 Data Data Adjusted to 2010
Fuel Average Payback, Average Payback,
Savings, years Project years
Average Project Cost, Cost,
(Range), % $000 $000
TPS 27(16-39) 28 12 36 9
SPS 19(13-27)* 58 34 74 24
* Lesser saving for SPS can be explained by the replacement of radiators
with baseboards, because existing radiators were not adaptable for
This information is necessary to properly interpret that
Steam heating conversion to hot water is especially difficult for
high-rise buildings: expensive high-pressure equipment, such as pumps,
valves, heat exchangers, etc., need be installed on every 14th -20th
mechanical floor. A prime example is the green retrofit at the Empire
State Building, where the main focus was the replacement of lights and
windows, but the seventy-eight year old steam system only underwent
minor changes (Rode 2009). The system runs on 3 psi steam, which comes
from a district grid, and four turbine-driven vacuum pumps that provide
a 3 psi vacuum. The total system pressure drop sums up to 6 psi (Douglas
"LONG ABSENT, SOON FORGOTTEN" TECHNOLOGY
Conversion to vapor/vacuum can solve the steam heating systems
retrofit problem efficiently and reasonably inexpensively. Vacuum
(negative pressure) steam heating, also known as vapor/vacuum systems,
became popular from the 1900-1930. These were TPS, where air was
discharged through a single vent valve in the basement as shown in
Figure 2. Because the volume of saturated steam at atmospheric pressure
shrinks approximately 1700 times when it condenses, the vacuum can be
formed if this phase change happens in a rigid, closed space like a
piping system. When the boiler stops and steam condensation creates a
vacuum, the air locking device blocks air from getting back into the
system. In some systems the vacuum is induced naturally while in others,
mostly larger ones, vacuum pumps are needed.
Many inventive vapor/vacuum heating designs and apparatus were
installed by old craftsmen. Quite a few of these systems are still in
service, puzzling modern HVAC professionals to this day.
Converting an ordinary steam system into a vapor/ vacuum system
generally improves the system's performance. Compared to ordinary
steam heating, vapor/vacuum has a number of benefits: soft heat because,
in the vacuum, water evaporates at lower temperature; higher fuel
efficiency; and no air hissing or water spitting from vent valves. These
merits come with a higher installation cost for TPS. Also, a larger
radiation area may be needed in some cases because the system operates
at a lower temperature. Air presence deteriorates the system's
performance, so the system should be kept leak tight.
[FIGURE 2 OMITTED]
In vapor/vacuum systems, the water in the boiler turns to steam at
a lower temperature. Presently, only steam TPS are converted into vapor
systems by means of vacuum pumps, resulting in the saving of fuel from
* Lower operating temperatures and less heat loss. Assuming room
temperature of 70 [degrees] F (21 [degrees] C), vapor temperature of 165
[degrees] F (74 [degrees] C), steam temperature of 218 [degrees] F (103
[degrees] C), and heat loss of 15%, the total theoretical reduction in
jacket and pipe heat losses would be 15% x (1 - (165 - 70)/ (218 - 70))
* Varying operating pressure to control vapor's temperature
depending on temperature outside. Such upgrades boosted fuel savings by
27% in a recent project (Green Buildings 2011) and claimed to be up to
40% for VARI-VAC technology.
Converting steam into vacuum would also resolve the inborn problems
of uneven steam distribution and building overheating, especially for
SPS. It was estimated in a study by the Minneapolis Energy Office that
for every 1 [degrees] F increase of internal temperature, the space
heating cost increases by 3%. An ordinary building's overheating of
14 [degrees] F (~8 [degrees] C) (from an average temperature of 7
[degrees] F [~4 [degrees] C]) corresponds to 21% more fuel spending
(Peterson 1985). An attempt to resolve the problem by additional vent
valves wasn't successful (EME Group 1994).
Long ago, the Paul system was the common solution for conversion of
steam SPS and TPS into vacuum systems. Here, vacuum is created in a
basement by a steam-powered exhauster, which is connected to air vent
tapping of each radiator (King 1908).
The vacuum had a dramatic effect on steam distribution. In most
cases the Paul system when retrofitted to an old reasonably tight
system, showed pay-back period of less then one heating season!
The fuel savings documented in the past were nearly 35% when system
was added to standard one pipe.
PROPOSED SOLUTION--VAPOR HEATING SYSTEM WITH NATURALLY INDUCED
Both SPS and TPS can be converted into VHSNIV by means of a simple
mechanical setup and operational procedures. The system is purged of air
by the steam and closed up. Cooling the system to 86 [degrees] F-122
[degrees] F (30 [degrees] -50 [degrees] C) causes steam condensation in
a closed volume and theoretically can create a vacuum of several inches
of mercury. See Table 2 (Engineering Toolbox 2011).
Table2. Saturated Water Vapor Pressure
Temperature Saturation Pressure
[degrees]C [degrees]F psia in. Hg
30 86 0 61 1.24
40 104 1.06 2.15
50 122 1.8 3.6
90 194 10 1 20.5
100 212 14.7 29.6
120 248 28.6 58.1
The feasibility of the new technology was tested on steam SPS
prototypes in the laboratory and a residential house. As an example, a
retrofit of an old (~100 years) single-pipe heating system to VHSNIV
cost $430 (excluding labor). The system consists of a boiler and six
radiators and is operated by existing controls with no additional
equipment required. Vacuum formation in the retrofitted steam heating
system before leaks were fixed is shown in Figure 3. After making the
system reasonably tight, the very first heating cycle created 24 in. Hg
of vacuum (-12 psig/2.7 psia). The system was off until the next
morning, and some air leaked in overnight. The next morning the system
started at 10 in. Hg (-5 psig/9.7 psia) and reestablished 20 in. Hg (-10
psig/ 4.7 psia). After three months of operation, 22 in. Hg (-10
psig/4.7 psia), 19 in. Hg (-9.5 psig/5.2 psia), and 17 in. Hg (-8.5
psig/6.2 psia) was retained for 165, 260, and 330 minutes, respectively,
after boiler shut off. This timing is adequate to keep the system under
a vacuum in cold weather when the boiler is cycling frequently. System
ability to maintain vacuum for longer time intervals decreased to 1-2
in. Hg (-0.5 to -1 psig/14.2 to 13.7 psia) after 13 hours overnight.
[FIGURE 3 OMITTED]
Figure 4 shows a comparison of the therms-per-day used by the
heating system. This comparison was made during time periods that had
the same average temperatures (from 2009-2010 before conversion and
winter of 2010-2011 after conversion). The therms usage data are from
gas company bills. The temperature averages are taken from a weather
station database. It should be noted that the apartment's occupancy
and heating behavior did not change in last 10 years. Observed energy
savings are in the 9%-16% range. It can be expected that a larger
heating system would have better savings. Additionally, depending on the
outside temperature, the vapor's temperature can be controlled by
changing system operational pressure/vacuum interval.
In deep retrofit systems and new VHSNIV installations, SPS are used
where condensate is returned from radiators while the system is cooling.
By having steam and condensate streams alternating on the same line,
water hammering is eliminated and a conduit of smaller diameter can be
employed. Neither water hammering nor thermal expansion noises were
observed when the concept of a periodic condensate return was tested at
14-16 in. Hg (-7/8 psig by 6.7/7.7 psia) on a copper tube with 0.5 in.
nominal diameter (12 mm) supplying steam to a 5225 Btu/h (5512 kJ/h)
radiator in the laboratory SPS.
The 25 feet (7.5 m) long copper conduit was enclosed in a 1 in.
nominal diameter cross-linked polyethylene (PEX) tube. With air in a 0.2
in. (5 mm) wide annulus, 98 [degrees] F-104 [degrees] F (37 [degrees]
C-40 [degrees] C) external wall temperature tube was observed for the
PEX tube; PEX is rated to 200 [degrees] F at 80 psi (93 [degrees]C at
0.55 MPa). Although insulation by air in annulus is not as efficient as
by commercially available foams, flexible PEX tubing is easy to fish
through walls, and copper tube can be pulled out/ pushed in for
replacement if required. Comparative data for insulated steel pipe and
copper tubing enclosed in PEX are presented in Appendix A for the same
The advantages of copper tubing enclosed in PEX are as follows:
* 9-12 times lighter, 3-4 times cheaper
* long bendable tubing, fewer fittings
* no rust, low maintenance
* 1.5 less heat loss from copper tube in PEX versus steel pipe in 2
in. thick insulation
In Figure 5, steel pipes enclosed in 1, 1.5, and 2 in. thick
insulation are shown to be compared with copper in PEX tubes, used for
the same steam load. For steel pipes, these diameters are required in
order to prevent water hammering in SPS. Corresponding copper tube
diameters were chosen to ensure a pressure drop below 2 psi on 100 ft
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
The option to use tubes of smaller diameters resolves the major
steam heating problems: high installation cost and heat losses.
Furthermore, modern solder-free technology can be utilized to connect
copper tubes up to 4 in. diameter and to save ~75% on installation time;
fittings are warranted for the copper tube life span.
System performance can be further enhanced if heat is delivered
into lightweight panel radiators. Typical temperature curves for
traditional high mass radiators and lightweight panels are shown in
Figure 6 for hot-water systems (Siegenthaler 2009). Fast system thermal
response rectifies temperature cycles. Panels emit heat mostly by
radiation, contrary to convection heating by hot-water baseboards
(Appendix B). Radiant heat is transferred by electromagnetic waves and
does not warm up the air between the heating unit and the recipient.
Also, with radiant heating, people feel comfortable at lower
temperatures, resulting in energy savings (McDonell 2009; NAHB 1994).
Such lightweight panel radiators are commonly seen in hot-water
systems in Europe (Figure 7). Their operating pressures of over 118 psi
(8 bar/813kPa) and temperatures of up to 248 [degrees] F (120 [degrees]
C) exceed the vapor system's operating parameters. Panels are
available in a variety of sizes, with heights ranging from 12-24 in.
(300-600 mm), lengths of 16-120 in. (400-3000 mm), and prices ranging
from $8-$65 as of this writing.
Without changing system piping and radiators arrangement, steam
from a district grid instead of a boiler can be utilized. VHSNIV can be
integrated into a district steam heating system loop in two ways:
* Single loop (Figure 8). After pressure reduction, district steam
is throttled into the VHSNIV. The amount of steam supplied is controlled
in order to keep the heating system at the desired vacuum level.
* Separated loops (Figure 9). A coil with high-pressure steam from
the district grid is used to control the temperature of the evaporator
in the VHSNIV system.
[FIGURE 7 OMITTED]
[FIGURE 8 OMITTED]
[FIGURE 9 OMITTED]
Comparison of a traditional steam heating system, a new VHSNIV
installation, and a hot-water system is presented in Table 3. Attractive
features are highlighted in gray. Of the three systems, VHSNIV has the
most attractive features. Compared to steam heating, VHSNIV imposes only
one additional requirement: less tolerance to leaks. Insignificant air
leakage into the system would not produce any damage, but with time the
system performance would deteriorate. To prevent this, VHSNIV can be
purged of air at any time and as often as required. Compared to hot
water, VHSNIV is superior with regard to a majority of parameters:
Table 3. Comparison of Heating Systems
Steam VHSNIV Hot Water
Pressure Up to 2 Negative 30-100 psi
psi up to
High pressure No no Yes
Temperature Per Per Zone
control radiator radiator
Heat content High High Low
kJ/kg 2100 2100 1.690 [degrees]
Btu/lb 902.8 902.8 0.4 [degrees]
Media No Yes Yes
Water make-up Yes No No
Maintenance Low Low High
Installation High Low Medium
Damage from Low No High
Noise High Low Low
Comfort level Depends High Medium
Humidification No No Baseboards--yes
Condensing No Yes Yes
Electricity No No Yes
Pumps, heat No No Yes
Heat type Radiant Radiant Convection
Heating time Medium Low Medium
Heat loss from High Low Low
SPS design Yes Yes No
Leak tolerance Yes Some No
* Safe pressure operating interval; no damage from leaks
* No moving parts, high-pressure equipment (pumps, expansion
system, differential pressure valves, etc.); low maintenance
* No mechanical floors for high-rise buildings
* Comfortable and efficient radiant heat versus convection heating
* SPS and per radiator controls versus zoned circuits; less piping,
* Can be electricity independent if steam is supplied by gas boiler
with millivoltage thermostat and pilot burner
* Simple metering
The cost of copper tubing is higher than the cost of plastic
tubing, which is used for hot-water heating. But copper fittings are
warranted for fifty years rather than five, ten, and a maximum of twenty
years for different plastic brands. So, for long-life projects, VHSNIV
is more attractive.
Modern leak-tight plumbing allows vacuum heating systems to evolve
into a closed system, which functions on water under a permanent vacuum,
such as a heat pipe. Similar copper heat pipes are commonly utilized in
solar heating applications, which operate at temperatures above 86
[degree] F (30 [degree] C) (Apricus 2011). A vacuum is created (and
recovered if ever necessary) at the start by either a vacuum pump or
steam ejector. The new system can utilize a condensing boiler as well as
a steam boiler. This opens up numerous opportunities to find new
concepts for the design, control, and operation of the system. Heat pipe
efficiency and reliability can be utilized in order to turn a
one-hundred year old inquiry into reality.
Unlike earlier TPS vapor systems, VHSNIV can utilize SPS as well.
Existing steam SPS and TPS can be converted into VHSNIV. If the steam
system is leak tight, changes are minimal but expected savings are
comparable to conversion to hot water.
For deep retrofits/new installations, energy efficiency can be
improved plumbing repair questions additionally by
* replacing steel piping with copper tubing, PEX insulation and
solder free fittings and using lightweight panel radiators.
Possible applications include but are not limited to new
residential and commercial buildings, existing steam system retrofits,
steam district heating systems, high-rise buildings, and combined heat
The author gratefully acknowledges support of this work from the
Shane Sweet and Bob Messia from New England Fuel Institute, MA
Frank "Steamhead" Wilsey from All Steamed Up Inc.,
David Tannozzini from PBD, City of Newton, MA Edward G. Ecock from
Con Edison, NYC
Robert P. Thornton and Laxmi Rao from International District Energy
Mark Ferri from MassCEC, MA
Ian Shapiro from Taitem Engineering, NY
Kent Stille from Runtal North America, Inc., MA
APPENDIX A COMPARISON OF STEAM CONDUITS--INSULATED STEEL PIPE AND
COPPER TUBE INSIDE PEX
Steam load 7 20
Conduit steel copper/PEX steel copper/PEX
Pipe size, 1 1 1/2
Inner tube 0.5/ 0.49 0.5/ 0.75/ 0.74 0.75/
-copper 0.49 0.74
Pipe/PEX 1.315/ 1.125 1.375/ 1.900/1 1.375/ 1.625
outer tube 1.049 /.862 1.054 .610 1.054 /1.244
Weight, 17.64 3.3285 5.0085 28.56 7.077 7.9905
inner tube 1.302 1.302 3.3705 3.3705
PEX 2.0265 3.7065 3.7065 4.62
Price . 42.28 23.52 37.275 61.25 42.147 50.862
inner tube 7.56 7.56 12.432 12.432
PEX - rated 15.96 29.715 29.715 38.43
Insulation 15.33 17.955
1.5" 27.3 31.08
2" 42.84 47.88
Pressure 0.593 0.518 0.757
No 134.3 13 12.6 188 14.2 13.9
insulation 31.6 41
1.5" 26.9 33.2
2" 23.7 28.4
Steam load, Ib/hr 65
Conduit material steel copper/PEX
Pipe size, inch 2 1/2
Inner tube -copper 1.125/ 1.125/
wall thickness 1.061 1.061
Pipe/PEX outer tube, 2.875/ 1.625 2 1/8
OD/ID 2.470 /1.244 /1.629
Weight (2), lb/126" 60.826 10.4475 12.9885
inner tube -copper 5.8275 5.8275
PEX 4.62 7.161
Price (3), $/126" 141.44 60.06 81.165
inner tube -copper 21.63 21.63
PEX - rated to 200F 38.43 59.535
Insulation price, 22.05
No insulation 274.9 15 14.3
insulation 1" 55.3
Steam load 3.2 9.1
Conduit steel copper/PEX steel copper/PEX
Pipe size, 1 1 1/2
Inner tube 12.7/ 12.4 12.7/ 19/18.8 19/
-copper 12.5 18.8
Pipe/PEX 33.4/ 28.67 21.9 34.9/ 48.3/ 34.9/ 26.8 41.3/
outer tube 26.6 26.8 40.9 31.6
, OD/ID mm
Weight 2.50 0.47 0.71 4.05 1.00 1.13
inner tube 0.18 0.18 0.48 0.48
PEX 0.29 0.53 0.53 0.66
Price (3) 13.21 7.35 11.65 19.14 13.17 15.89
inner tube 2.36 2.36 3.88 3.88
PEX - rated 4.99 9.28 9.28 12.01
Insulation 4 79 561
1.6" 8 53 9.71
2" 1339 14.96
Pressure 13.41 11.72 17.12
No 464.9 45.0 43.6 650.7 49.2 48.1
insulation 109.4 141.9
1.5" 93.11 114.9
2" 82.03 98.3
Steam load (1),kg/hr 29.5
Conduit material steel copper/PEX
Pipe size, nominal 2 1/2
Inner tube -copper 28.6/ 26.9 28.6/
OD/ID mm 26.9
Pipe/PEX outer tube, 73.0/ 41.3/ 31.6 54.0/
OD/ID mm 62.7 41.4
Weight (2), kg/m 8.63 1.48 1.84
inner tube -copper 0.83 0.83
PEX 0.66 1.02
Price (3) . S/m 44.19 18.77 25 36
inner tube -copper 6.76 6.76
PEX - rated to 200F 12.01 18.60
Insulation price 6 89
Pressure drop (4),
Heat loss, kJ/linear
No insulation 951.5 51.9 49.5
insulation 1" 191.4
WAY OF HEAT TRANSFER--RADIANT VERSUS CONVECTION
[FIGURE B1 OMITTED]
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Igor Zhadanovsky, PhD
Igor Zhadanovsky is president of Applied Engineering Consulting
(AEC), Newton, MA.