Almost all housing in the US uses solely active systems for heating and cooling. The advantage is immediate fine-tuning of the interior climate regardless of exterior conditions. The disadvantage is a dependence on the use of costly, non-replenishable, difficult to harvest, and polluting fuels. UrbanEden is part of a new paradigm. First, overall system load demands are considerably reduced through implementation of a high performance building envelope. Next, passive and hybrid systems provide the lion’s share of these reduced loads, relegating active systems to essentially a supplemental and back-up role. This allows smaller, hyper-efficient active systems to be utilized to fulfill the remainder of the already tiny building loads.
Mini-Split Heat Pumps
The primary means for cooling UrbanEden is a hybrid hydronic fluid mat system of capillary tubes embedded in the walls of the house. However, in consideration of the high temperatures and humidity reached during the summer months in the southeastern United States, UrbanEden also makes use of two Trane Residential® Mini-Split Heat Pump units to supplement the capabilities of the hydronic mats. The units' combined 1.5 tons of capacity are used to affect dry-bulb temperatures and provide assurance that interior climate will be suitable for occupants, even in the region’s harshest climate-extremes. In this sense the mini-split heat pumps satisfy the peak cooling loads, which cannot be met through hydronic mat operation alone. Additionally, the mini-split heat pumps can alone meet UrbanEden’s peak heating load during the winter.
Though the Trane minisplit heat pumps effectively regulate relative humidity, the extreme demands of the Solar Decathlon competition, namely thousands of people touring the house continuously, require additional dehumidification capabilities. This anomalous load on UrbanEden’s interior spaces is controlled and monitored by a stand-alone Ultra-Aire 70H ducted dehumidifier unit which enables the home to regulate the relative humidity of its interior air independent of its temperature. This additional dehumidification capacity will also prove beneficial during public tours of the house at its permanent home as an education and research center at the UNC Charlotte campus.
Energy Recovery Ventilator
Most houses access fresh air through leaks around windows, under the sill plate, or through the insulation in walls, floors, and ceilings. However, as a consequence of UrbanEden’s tight building envelope, a supplementary means of ventilation is required to satisfy ASHRAE’s air exchange rate minimum requirements for residential structures. Compliance with these requirements is ensured and exceeded through application of a Trane Residential FreshEffects™ Energy Recovery Ventilator (ERV).
The Trane ERV is fundamentally a high efficiency fan that periodically exchanges stale indoor air with fresh outdoor air by moving it through an ingenious heat exchanger. During the air exchange process, a static-plate-energy-core within the ERV moves sensible heat (dry bulb temperature) from exhausted indoor to fresh outdoor air stream or vice versa based on the season. Simultaneously, during cooling seasons latent heat is passed from fresh to exhausted air streams resulting in passive dehumidification of incoming fresh air. The result is maintenance of a near consistent temperature and humidity level within the house while supplying and circulating fresh air throughout the interior spaces.