This project demonstrated that radiant panel cooling/heating can be combined with envelope thermal mass and convective dehumidification/ventilation for year-round comfort in the hot arid climate. The final report provides extensive data that can be used by researchers, simulation developers, and design engineers. A control strategy was developed that was able to maintain conditions within the ASHRAE standard for thermal comfort for the continuous annual cycle monitored and at less than half the operational costs of a typical system.

RADIANT TECHNOLOGY BEST UTILIZES THERMAL MASS
With proper design, most, if not all of the residential cooling can be accomplished off peak. The passive adobe walls were not as effective during the latter parts of the heating and cooling seasons as the active thermal mass of the concrete/flagstone floor in shifting the load from on-peak to off-peak. But the adobe walls play an important role in the early summer and winter seasons and during the thermal sailing seasons.

UTILITY RATE IS A KEY TO LOWER OPERATIONAL COSTS
This demonstration came very close to shifting the entire cooling load to off-peak. It still may be possible, but the rate structure is one of the key factors to making this happen. The electric utility might consider reducing its 12-hour on-peak window to maybe 10 hours or even 8 hours to encourage designers to use thermal mass for shifting the load to off peak.

HYDRONIC SYSTEM SAVES ENERGY
The efficiencies of moving energy by pumping water through pipes with fractional horsepower motors rather than by blowing air through ducts with fans are significant.

ALTERNATIVES TO THE HEAT PUMP
The water to water heat pump provided the hot and cold water needed for the hydronic system. The ground loop for the heat pump was adequate for the winter operation but not for the summer operation. Low cooling capacity of the ground loop necessitated installation of a closed loop evaporative cooler, described below. The ground loop proved to be too expensive for what it provided.
An alternative plant would include a separate chiller for cooling and a solar panel/boiler backup for heating. The water-cooled chiller would reject heat to an evaporative condenser such as is currently being used as a closed loop evaporative fluid cooler. The fluid cooler proved very efficient, reducing the condensing temperatures by over 30F. Then, in the winter, solar panels would be the primary source of heat to the hydronic system, with a small gas fired boiler for back up.

EVAPORATIVE CONDENSER/FLUID COOLER
This unit was used as a fluid cooler rather than an evaporative condenser to boost the capacity. It proved to be an extremely good investment. It reduced the condensing temperature of the heat pump in cooling mode by over 30F. It boosted the cooling capacity of a three-ton unit by over 25%. It also proved to require very low maintenance, with simple end of season cleaning and no corrosion.
If used as an evaporative condenser, replacing an air-cooled condenser on the conventional air conditioning system, it would have similar benefits and would have a quick payback on investment. A research project should be conducted to quantify the advantages of using such a unit.

PROVIDING A SEPARATE AIR SYSTEM FOR DEHUMIDIFICATION AND VENTILATION IS COST EFFECTIVE
Decoupling the sensible and latent equipment improves control response and prevents unneeded dehumidification (Mumma 2002). In an all-air convective system, if it is oversized, as is frequently the case, the relative humidity can vary widely and be above the upper limit. By controlling the humidity with separate equipment controlled by a separate humidistat, the humidity level will always be under control and there will be no danger of condensation.

USE OF LIGHT WEIGHT RADIANT CEILING PANEL PROVIDES QUICK RESPONSE
The ceiling panel is a very efficient use of compressor time, particularly during on-peak hours. For this extreme climate, the high mass floor absorbs much of the sensible load, but can't cover all of it. When additional capacity is needed, higher temperature chilled water through the ceiling panel can quickly absorb the peaks.

CONDENSATION DOES NOT APPEAR TO BE A PROBLEM.
In this project, the temperature of the chilled water flowing into the house was adjusted, as necessary, to be above the interior dew point. Thus, supply pipes and panel surfaces were always warmer than the dew point in the space. However, if the dew point would rise above the 62F upper limit, the humidistat would operate the dehumidifier.

THE ULTIMATE COMFORT CONTROL
A system that uses radiant surface control in combination with thermal storage of the building's mass, and a separate system for dehumidification and ventilation would appear to be the ultimate method for providing thermal comfort. It would provide the type of comfort, on a year round basis, that one experiences on that "perfect" spring or fall day when the climate and the structure provide the ideal conditions for the body.

THE "SEASONAL TEMPERATURE"
This has proven to be a good indices for making control decisions. The sensor, buried in the wall mass, gives a good indication of the season and provides a close approximation of the average daily temperature over the past 24 hours. Burying a sensor in a "standard mass" would be worth considering for the more complex residential and small commercial control systems as a reference temperature, and the basis of making decisions.

HEAVY MASS CONSTRUCTION - ADVANTAGES AND DISADVANTAGES
Mass construction can be a passive component or an active component of the environmental control system. In the Carefree project, the exterior and some interior walls were a passive component. The exterior passive walls could, at some periods of the year, be a thermal liability. During the late summer, their temperature did not drop much below 80F. So, from the comfort standpoint, they were a slight liability.
Passive heavy thermal mass construction
Heavy mass construction has advantage during a thermal sailing season and during winter and summer periods when the seasonal temperature is ramping toward the extreme. For instance, in the early summer, there is an advantage when the temperature of the mass of the walls is lower than the outside daily mean and ramping up. Likewise, there is an advantage in the early winter when the mass temperature is higher than the daily mean. However, there is a disadvantage in the winter when the mass' temperature is consistently lower than the daily mean, and in the summer when the mass' temperature is consistently higher than the daily mean.
Active Heavy Thermal Mass Construction
In the Carefree house, the heavy mass floor was capable of active control. It was originally meant to be used actively for winter heating and passively during the cooling seasons, but half way into the second cooling season it began to play a minor active role (it was cooled to about 76°F). Then, in the third cooling season, the floor took on a greater and greater role as its temperature was further reduced (finally to 73°F) to achieve increasing amounts of thermal storage. The strategy of the third cooling season was to keep the optemp below 78.8°F (26°C) with a minimum amount of on-peak compressor run time.

STABLE TEMPERATURES
Stable temperature and humidity levels reduce the deterioration of materials. Inside the insulated envelope of the Carefree house, during the entire year, very moderate temperatures exist. That should extend the life of both the system and the surrounding construction materials. In the heating season, the highest water temperature used (because water is heated by heat pump and not a boiler) is less than 105°F going to the floor, and less than 85°F going to capillary tubes in the plastered ceiling. During the winter, the ceiling assembly is maintained above 68°F. During the summer, the ceiling assembly is maintained below 85°F. Thus, the largest annual temperature variation in the ceiling is less than 20°F. This will prolong the life of the capillary tubes in the ceiling. For the floor, it appears that a surface temperature of between 71-73°F is the ideal temperature for both summer and winter. This should extend the life of the tubes in the floor. The interior plaster of the adobe walls will remain between 65°F and 82°F, a 17°F swing from winter to summer.

CONTROL SYSTEM RELIABILITY AND COMPLEXITY
A reliable programmable control system is essential if advantage is to be taken of thermal storage and low energy strategies. The system must provide for multiple analog inputs, must adjust to a varying utility rate schedules. Condensation control is most critical, so the determination of dew point temperatures must be based on high quality instruments.
The control system for a radiant/convective system requires greater sophistication than the traditional home thermostat. It has the advantage of providing for varying zones and activities and monitoring more variables that allow taking advantage of low energy opportunities can lead to greater energy savings
The control system for this prototype demonstration project was a fully programmable commercial grade installation. In this project, complexity was required for the following reasons:.
1. Dehumidification requirements to prevent condensation must be a top priority. This would necessitate the use of high quality humidity sensors and the calculation of dew point temperatures.
2. Because a radiant system can only transfer sensible heat, there must be a separate dehumidification system requiring control. The conventional convective system often removes latent heat, whether it is needed for comfort or not (an unneeded expense). The radiant system's separate dehumidification system only removes the amount of latent heat needed to keep the space dew point below 62F (comfort requirement), or to keep the dew point below the lowest surface temperature in the space (condensation prevention), which ever of the two is lower.
3. Taking advantage of the time of day rate structure requires scheduling and the use of changing set points for on-peak and off-peak periods. This allowed a reduction in the energy costs for environmental controls by over 66%.
4. Zoning provides for the changing loads experienced in various areas of the house and provides opportunities for capacity reduction and energy savings.
5. Energy savings can be achieved in the operation of the Energy Recovery Ventilator by comparing the enthalpy conditions in the indoor and outdoor air.

LEAKS -- RISKS OF A RADIANT SYSTEM.
Burying tubes or pipes in inaccessible construction is a risk. No material will last forever and provisions should be made when such a system is no longer serviceable. Plastics loose flexibility over time, particularly when exposed to higher temperatures or large swings in temperature. Access should be provided to service such a system, and to replace it with another type of environmental control system when its life is finished. Deterioration of materials is accelerated by temperature extremes and large variations in temperatures over a day or over a year.

PROVIDE BACK-UP
Providing a conventional duct distribution system, sized for a conventional convective system load, should be provided when the house is new. During the life of the radiant system this ductwork could distribute air for ventilation and dehumidification requirements. If and when the radiant system needs replaced, hopefully 40-50 years (up to 100 years), space provisions have been made for the replacement equipment.