Radiator Valves Prevent Apartment Overheating

This thermostatic radiator valve is designed for hot water and one-pipe steam systems. Acting as an adjustable air vent, this valve prevents apartment overheating and significantly reduces space heating energy use.

Energy auditors cringe when they see open windows cooling off overheated apartments on cold days. By preventing apartment overheating, thermostatic radiator valves (TRVs) can cost-effectively reduce space heating energy use, according to a recent study in New York City. The average payback was three years on an installed price of $50 per TRV, but some buildings and individual apartments benefited from the retrofit more than others.

TRVs have been used for decades to control steam in radiators, but most steam-heated multifamily buildings in New York City do not have them. The low-pressure, one-pipe gravity return system is the most common steam distribution system in the buildings (see "Converting Steam-Heated Apartment Buildings," HE May/ June '88, p. 23). In these closed-loop systems, steam generated in the boiler and distributed to radiators returns in the form of condensate to the boiler. Air vents permit air to enter and leave the system. By controlling radiator air pressure, the vents indirectly regulate the radiator's temperature.

A TRV is a temperature-regulated control valve that functions as an adjustable air vent. It can maintain a lower room temperature by restricting the air flow through the vent, limiting the amount of steam entering the radiator. It can maintain a high room temperature by not restricting air flow from the radiator, thus allowing it to fill with steam quickly. The TRV has an adjustable temperature setting knob to control the rate at which air flows through the vent.

The New York State Energy Research and Development Authority (NYSERDA) contracted the EME Group to evaluate the effectiveness of TRVs in eliminating overheated apartments and saving energy. The group also identified problems with TRV installation and maintenance and assessed occupants' responses to the use of the valves. EME installed a total of 224 TRVs. The group monitored energy consumption for three years (1991-1994) in eight privately owned multifamily buildings. Each building had 18 to 84 occupants in 15 to 26 apartments. Space heating energy was determined by monitoring and recording apartment temperatures, boiler fuel consumption, and domestic hot water (DHW) use.

All of the buildings had one-pipe, low-pressure steam distribution systems. The boiler equipment was in good operating order, the building envelopes were in good condition, and systems had even steam distribution and no problems with wet steam or water hammer (collision between steam and condensate that creates a "banging" noise in pipes). To participate, building owners had to upgrade their heating plants by insulating bare steam pipes, tuning burners, making minor repairs to the steam distribution system, and replacing inoperative or undersized air vents on radiators and steam mains. After building owners took the necessary measures, EME recorded baseline data for 12 months.

EME used a "fuel computer" to collect hourly data on fuel consumption (oil or natural gas), outdoor and indoor apartment temperatures, boiler run time, boiler flue gas temperatures, DHW consumption and supply temperatures, incoming city water temperatures, and boiler makeup water flow.

EME installed TRVs with setpoints of 72^oF in half of the apartments in four buildings and recorded data for another year. The installers selected south-facing apartments that had excessive solar gain, top-floor apartments, apartments identified as overheated, and apartments with radiator temperature sensors. EME collected data for these units during another heating season, and then installed TRVs in the remainder of the apartments in three of the buildings. The fourth building was dropped from the study because the owner installed a new heating system, and a fifth building was fitted with TRVs in half of the units. EME decided not to install TRVs in three of the eight buildings due to changes that conflicted with EME's initial building criteria.

One building, which was not overheated before the retrofit, showed no savings. In the other buildings the partial installations saved an average of 9% of annual heating use. After full installation, the average annual heating use savings totaled 15%. The average annual cost savings after full installation was $1,100 per building with an average payback of three years. Payback ranged from one to five years in those buildings where TRVs produced energy savings. EME based annual energy savings, cost savings, and simple paybacks on a natural gas or oil cost of 70 cents/therm and $50 for each installed TRV.

Based on these results, EME recommends installing TRVs on one-pipe steam distribution systems in

• Apartments that are heated above 72^oF.
• Apartment buildings where the existing control system causes temperatures to fluctuate above 72^oF.
• Specific rooms in which the radiator has become oversized due to the installation of thermal-pane windows.

-Ted Rieger

Ted Rieger is a freelance writer based in Sacramento, California, who specializes in energy issues.
 
 

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