Solar Decathlon is changing with the times

Jan. 1, 2012
With energy use being closely monitored and judged for the Solar Decathlon competition, the entire home’s systems-package must be one that enhances efficiency while still maintaining comfort and required dehumidification.

With energy use being closely monitored and judged for the Solar Decathlon competition, the entire home’s systems-package must be one that enhances efficiency while still maintaining comfort and required dehumidification. For example, at 2:00 P.M. each day, the students’ homes at the Solar Decathlon have just one hour’s time to restore temperature and humidity to pre-determined levels. The week’s wet weather created foot-traffic that deposited soggy trails inside each of the homes. Inverter mini-splits throughout the homes were able to meet, or beat, the required humidity-level standards. While it’s unfortunate that hydronic radiant floors were a casualty of the cost factor, I believe we are also witnessing the advent of a new mini-split revolution that will include lots of air-to-water hybrid radiant heating/cooling systems that utilize the same condenser to target humidity while using an ultra-quiet and much smaller recessed-and-concealed variable-speed air-to-air mini-split air handler, which incorporates high-efficiency fresh-air exchange. As an added bonus, that same air handler will be able to serve as second-stage heating/cooling, so that programmable controls will allow the heating/cooling to hibernate while still maintaining dehumidification and freely exchange indoor with outdoor air to enhance the indoor environment.

Gazing into my crystal ball, I’m going to suggest a fundamental shift will have occurred by the time the next Solar Decathlon arrives in 2013. Radiant cooling has begun to gain traction in the U.S. We all know that radiant heating works as well installed in ceilings and walls as it does when installed in floors. (My brother and his wife are enjoying a cocoon of comfort in their newly remodeled kitchen: from steam heating to hydronic radiant in the ceiling, remodeling left no room for any radiators.) Radiant cooling installed in ceilings is simply amazing to experience first-hand and extraordinarily economical to operate if it is designed and installed properly. Been there, done that in hostile hot and humid indoor conditions during a small business grand opening. The office-side central ducted air conditioning system was unable to keep up with the constant opening/closing of the main entry door and gathered throng. However, the packed conference room immediately adjacent via its open double doorway was a stark contrast in comfort: with 65°F water circulating, above the dew-point, through the radiant ceiling, the room was perfectly comfortable.

The Solar Decathlon students’ response: Operating efficiencies for Daikin’s Altherma air-to-water inverter heat pump come close to top-end geothermal model efficiencies, and at a fraction of the cost. As you would expect from engineering students, they studied the operating costs and correlation between water temperatures for heating/cooling as they relate to COP. One team concluded that production of DHW would be done exclusively via their Altherma and that their analysis of total lifetime costs resulted in the elimination of the solar thermal side of the DHW! However, bear in mind that the PV solar panels were designed to offset 100% of the electricity required to power the Altherma during peak-load in daylight while the indirect was sized to store sufficient DHW until the next day’s sunshine would be available. Given that the Solar Decathlon homes are grid-tied, a return to hydronic radiant heating with cooling included could provide the teams with thermal storage batteries sized to provide comfort between sundown and sunup while utilizing an ECM circulator sipping less than 10-watts per hour.

Other mini-split manufacturers tell me they too have beta-test air-to-water units in place undergoing real-world studies and plan on bringing systems to market in the near future. Our world is changing and this year’s Solar Decathlon competition mirrored those changes with a glimpse into the future of blended systems technology. Our second Daikin Altherma hybrid system is sold and scheduled for installation.

2016 is not very far off in the distance when the 30% federal tax credit for geothermal systems expires. Bear in mind that a customer can only get back the taxes paid in via withholding each year, and, as a result, they may find it’s necessary to carry-over the tax credit in multiple years to take full advantage of the program. That affects our opportunity for promoting a 30% tax credit that may be cut short and become a smaller percentage as we approach the Dec. 31, 2016 deadline. Visit for details on available tax credits and incentives available for your location. The 30% geothermal tax credit essentially voids the costs for the geothermal wells. If the tax credit is not extended, renewed, or enhanced, promoting and selling geothermal systems will face an uphill battle. It’s time to begin preparing for the one thing besides death and taxes that’s constant: change.

To quote Bob Dylan from The Times They Are A-Changin'

"Come gather 'round people
Wherever you roam
And admit that the waters
Around you have grown
And accept it that soon
You’ll be drenched to the bone
If your time to you is worth savin'
Then you better start swimmin' or you’ll sink like a stone
For the times they are a-changin'"

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