Conclusions > Design Lessons Learned
 Guidelines for Implementing Heat Recovery Solutions

Design Lessons Learned

Greywater Heat Recovery

When planning large recreational and hotel facilities, incorporate greywater heat recovery systems into the initial design.

These systems:

• Have a very low initial cost,
• Can be fabricated and installed by a skilled plumber,
• Use common materials,
• Contain no moving parts,
• Require little to no maintenance,
• and in a commercial setting, can have a payback period of less than six months

To maximize the recovery potential:

• Preheat the cold water entering the building before it reaches the boiler.

Given the choice between preheating the cold water coming into the building, and reheating circulating pool water, the heat exchanger should be installed to preheat the entering cold water. This will maximize the temperature difference (and efficiency) in the heat exchanger.

Greywater heaters can be used to preheat the cold water going to shower heads or to boilers. In large facilities, the temperature of the water leaving the shower head needs to be carefully controlled, so the heat exchanger should be used to preheat water going to the boiler. This also allows heat recovered from the showers to be used for other purposes, like preheating water to be added to pools.

• Minimize heat lost in transportation of the greywater.

Minimize the distance between the source of the hot greywater, the heat exchangers, and the water heater.

Insulate drainpipes until the reach the heat exchanger, especially if they are running through a concrete slab.

Airborne waste heat

Laundry Facilities

Laundry dryers are a large source of waste heat, but there are significant obstacles to overcome to making use of this heat. Any heat recovery system would have to deal with both condensation in the exhaust tube and lint. Because air-to-water heat exchangers can be problematic, an air-to-air process might be more appropriate. Potential uses include:

• Preheating air entering the building during the wintertime.
• Preheating the air entering the laundry room. This could help ensure adequate ventilation and shorten drying times.
• Heating large spaces.
• Preheating air before it enters the furnace

One possible method of dealing with the lint and condensation, suggested by Tom St. Louis, is to run drain water down the exhaust pipes. This would clear the lint from the exhaust tube walls, but might require significant plumbing to be installed as part of the laundry dryer system.

Pool Ventilation

In northern climates, another significant source of waste heat is the ventilation needed for the poolrooms. The air exhausted is hot and moist, containing significant heat when compared to the cold, dry outside air. However, this air also contains a significant amount of corrosive chlorine, making the choice of heat exchangers very important. Try copper counter-flow heat exchangers or heat exchangers with glass manifolds.