Direct Contact

SACRE-COEUR HOSPITAL, MONTREALDESSAU-SOPRIN

The Hpital du Sacr-Coeur is a 700-bed, 74,000-m2, facility in the northern part of Montral island. The main structure dates from 1925 and was built to house patients with tuberculosis. Over the years several additions and upgrades have been made, including the addition of a residential unit for the Soeurs de la Providence in 1960. The nuns ran the hospital for 50 years.

Last year, Laurier Nichols, ing. of Dessau-Soprin consulting engineers, won an ASHRAE Technology Award for the design and renovation of the hospital’s heating plant. The project has shown the real benefits of direct contact technology in heating processes and has inspired the realization of several other projects. These include the Charles Lemoyne Hospital in Longueuil, the Montreal Jewish Hospital and the Laval University Hospital Centre in Quebec City whose systems were designed by Dessau-Soprin.

The heating plant

The Sacr-Coeur boiler room from 1925 is a separate building linked to the main building by an underground tunnel. It originally included three coal fired, 450 HP (4,350 kW) steam boilers. In 1960, two 650 HP (5,800 kW), grade six oil fired boilers were added. Before the most recent renovation all the boilers could burn either heavy (grade 6) oil or natural gas.

Steam generated at 125 psig (860 kPa) was used for heating the building, the nuns’ residence, the air for ventilation, domestic hot water, and for the laundry, cooking and sterilization equipment.

Over the years, many problems were identified with the operation of the heating plant. These problems included low efficiency, the requirement for continuous 24 hour supervision and the unavailability of spare parts. As well the plant was emitting pollutants (SOx ) into the environment.

The renovation aimed to improve the plant’s efficiency, lower the supervision and maintenance costs and lower the emitted pollutants.

All these aims were achieved. The annual natural gas consumption has been reduced by 600,000 m3. The total output of all the boilers in simultaneous operation is now less than 12,000 kW, thus there is no more regulatory need for continuous supervision. The new equipment saved on the maintenance required and it operates with very low atmospheric rejection (fewer than 200 ppm of CO and 40 ppm of NOx.

Annual savings generated by the complete renovation of the heating plant were $88,000 (supervision), $170,000 (energy), $40,000 (maintenance), totalling $298,000. The total cost for the renovation was $1,340,000, giving a simple payback of four to five years.

Two energy efficient components were the key to the success of the renovations at Sacr-Coeur: a direct contact water heater and a direct contact condensing stack economizer. These are described in the figures above. CCE

Client: Sacre Coeur Hospital (Marcel Brabant, chief of building services)

Mechanical and electrical consulting engineer: Dessau-Soprin, Montreal (Laurier Nichols, ing., Gerald Boily, ing.)

Direct contact technology: Natural Gas Technology Research Centre, Boucherville

Equipment supplier: SOFAME

The flue gases of a standard boiler generating steam at 125 Psig are normally in a range of 450F (232C) to 500F (260C). A tremendous increase of total plant efficiency can be achieved if the flue gases can be lowered down to 100F (38C) as with this system.

The hot combustion gases of the two 600 HP (6,000 kW) standard boilers are introduced into the economizer by a new induced draft fan. The water to be heated is sprayed at the top of the unit over a bank of stainless steel nodules where it is in direct contact with the hot flue gases. During the night hours, to take into account the variable heating requirement for domestic and laundry hot water, heated hot water is accumulated in a reservoir (6,000 gallons or 22,700 litres) located at the bottom of the economizer. The temperature of the flue gases exhausted from the economizer is usually 10F (5.6C) higher than the temperature of the water sprayed over the bank of nodules.

When the laundry uses a large amount of hot water, the water make-up of the unit is at its lowest temperature and the exhausted gases could be as low as 50F (10C).

The condensing stack economizer works most efficiently when the make-up water is low temperature. In winter the heating of the air supplied to the boiler room also contributes to lower the temperature of the water sprayed at the top of the stack economizer, thus increasing the total equipment efficiency.