Most households in Canada dry their laundry in clothes dryers that tumble the clothes in warm air. While hanging clothes on a clothesline outdoors when the weather permits is the most economical and most gentle way of drying, machine drying is more convenient and usually faster, but consumes a considerable amount of energy. All dryers use electricity to power the controls and the motor that drives the drum, but for heating the air that dries the clothes, either electricity or natural gas can be used. There are approximately 9.8 million dryers in use in Canada, 96.9% of which are heated with electricity, and the balance (3.1%) with natural gas. The popularity of gas dryers varies across Canada, since the availability of natural gas and price difference between electricity and natural gas vary considerably from province to province. Ontario and Alberta lead the country in the concentration of gas dryers (with 7.7% and 10.2 % respectively) and Quebec has a very small number, but is growing due to the local utility's efforts to increase availability and market share of natural gas. In the USA, about 20% of the clothes dryers are heated with natural gas; their higher popularity compared to Canada is partly the result of a larger difference between electricity and natural gas prices in the USA.
It is estimated that in Canada, dryers consume a total of 26.4 PJ of energy per year, equivalent to 7.2 billion kWh of electricity.
What are condensing dryers?
Condensing dryers are electric dryers that do not have or require an exhaust vent. There are no condensing gas dryers, since the combustion products of gas dryers must be exhausted for safety reasons. Unlike vented dryers condensing dryers recirculate the air in the drum between an electric heater and a water-cooled condensing coil, or water-spray cooled condensing chamber. Tap water for condenser cooling is drawn from the cold water tap and discarded down the drain.
Less common are condensing dryers with an air-cooled condensing coil. The condensed water is collected in a removable container for manual disposal when the holding tank is full. For these air-cooled condensers, the cooling air is drawn from the room and returned to the room at a higher temperature. Since the moisture from the clothes ends up in the holding tank, none of it ends up in the indoor air.
Condensing dryers available in the market
There are a few stand alone condensing dryers in the market, and most appear to be of the air-cooled condensing type. The only other condensing dryers available are in the form of a combination washer-dryer and they appear to be of the water-cooled condensing type. This class of appliance has a single drum for both washing and drying. It has a single source of power (120V standard cord) a single control for both washing and drying, and connectors to the cold water supply and drain.
A combination washer-dryer is much more compact than a conventional laundry washer and dryer pair because it is a single appliance with a single drum for both washing and drying. Some models can be converted to portable units by adding casters and a special hose coupler for the tap in a sink. Other models are suitable for installation under counters, in a similar manner as built-in dishwashers.
Performance of Condensing Dryers
There is no test standard to measure the efficiency of condensing dryers. Combination washer-dryers that have condensing dryers must be tested and verified for the clothes washing function and can be labeled voluntarily according to the requirements of the Energy Efficiency Regulations. The pointer on the EnerGuide label for these models indicates the energy consumption of the washer function only, but not the consumption of the dryer.
Stand-alone, air-cooled condensing dryers have the advantages of high capacity and efficiency and the ability to dry simultaneously and independently of the washer.
Combination washer-dryers with a condensing dryer have a number of advantages over a conventional laundry pair:
- The single appliance occupies less space than a conventional laundry pair.
- Can be located in any place with a source of cold water, a drain and an electrical outlet and no vent to the outdoors is required.
- Can be built into cupboards or under counters.
- Some are lower in first cost than a conventional laundry pair
- Combination washer dryers can be programmed for unattended wash and dry without having to transfer the clothes between appliances.
- The washing function in all combination washer-dryers tends to be more energy efficient than most top loading, vertical axis washers because they use a horizontal axis front-loading design. Front loading washers do a better job of washing clothes, while saving energy, water and detergent at the same time.
- Combination washer dryers have high spin speeds that remove more water from the clothes than vertical axis models (less water is left in the clothes after the final rinse, saving energy in drying when compared with top loading washers.)
- Most units have an internal heater that heats up the wash water as required
- Can be easily disconnected and moved on casters in "portable" applications and connected easily to a tap by a sink.
- Some units have a moisture sensing control for the drying function to avoid overdrying.
On the other hand, these combination appliances have a number of disadvantages that affect their popularity in Canada:
- The drying function is very slow and not very efficient.
- The duration of a complete wash and dry cycle is much longer than for conventional laundry pairs. (Two to four hours have been reported) Users indicate that only half a load can be dried at one time due to the small drum size and low dryer performance.
- Unlike a laundry pair, the combination washer-dryer cannot be used to dry one load while washing the next load at the same time, an inconvenience for people who save all the laundry for "laundry day" and want to get it done as quickly as possible
- All condensing combination washer-dryers use cold tap water to condense moisture removed from the clothes, at additional cost
- Because of the long wash-dry cycles, manufacturers recommend not saving all the laundry until the weekly "laundry day", but rather to do one load per day as needed; stretching laundry days across the week may not be acceptable to some people.
Energy Consumption of Condensing Clothes Dryers
It is estimated that that an average family using a standard size vented dryer will go through 416 laundry drying cycles per year, consuming about 925 kWh of electricity to operate the heater, motor and controls. This information is based on a 3.17 kg average laundry load.
The energy consumption of condensing dryers has not been established because there is no standard test method. However, since vented dryers remove moisture more efficiently than condensing dryers, we expect condensing dryers to be somewhat less efficient than vented dryers, as far as the drying of clothes is concerned. However, condensing dryers that are part of a combination washer-dryers is likely much less efficient than vented dryers for a different reason described below.
Typical combination washer dryers are designed to take standard size wash loads and dry them in the same drum that effectively is undersized for drying purposes. In this case, the efficiency of the dryer will be well below optimum for the reasons described below.
The size of the drum of most combination washer dryers available tends to be around the lower size limit of a "standard" washer. A washer above 45 litres is classified as a "standard" size. Standard washers currently in the market range between 45 and 102 litres in drum capacity.
On the other hand, as a dryer, the drum size puts these machines near the lower end of "compact" sized dryers. A dryer below 125 litres is classified as a "compact" dryer.
Dryers rely on the tumbling action to move the clothes through the warm air in the drum to dry efficiently. However, since combination washer dryers have a severely undersized drum size for drying, clothes tend to pack and dry unevenly, taking longer and more electricity to dry than properly sized dryers.
Combination washers-dryers have one inherent shortcoming: as a washer, the drum can take a certain size of load. As a dryer, however, the drum would be too small to dry the same amount of clothes efficiently.
With combination washer-dryers it is important to wash natural fabrics such as cotton towels separately from synthetic fibres, because during the drying portion of the wash-dry cycle, natural fabrics retain a lot of moisture and dry slowly. Synthetics hold little water and dry quickly. Therefore, for best efficiency and shortest drying time, wash and dry natural fabrics together and wash and dry synthetics together, but avoid washing and drying natural fabrics together with synthetics.
One manufacturer of combination washer-dryers specifies that their ventless washer-dryers consume 15 litres of cold water per load to condense the moisture removed from the clothes. Users have reported these appliances consume between 8 to 40 litres of cold water per load for condensing the moisture depending on brand, model and size of the load.
In addition to this limitation, condensing dryers have a much reduced capability of removing moisture from the hot air than a vented dryer, further increasing the amount of time and electricity required to dry the clothes.
Stand alone air-cooled condensing dryers are the only dryers that safely recover the energy used for drying clothes and release the heat (but not the moisture from the clothes) indoors. This heat energy will be useful during the cold months to heat the building, but may add to the air-conditioning load during hot days. The condensed water retained in the holding tank can be re-used in steam-irons, since the water is distilled and very clean, leaving no scale or sediment in the iron or on the clothes.
In summary, condensing dryers take considerably longer to dry than vented dryers, consume more energy and may result in more wear on the clothes as a result. Water cooled condensers discard the recovered heat and water from the condenser down the drain with no further re-use.