Las Cruces is located in a high desert climate. The weather is characterized by low humidity and abundant sunshine. The low humidity and relatively high elevation contribute to the large temperature swings encountered during the year. The winter days are usually sunny and mild, with a substantial temperature drop at night.
The summer has hot days and cool nights with low humidity early in the summer, increasing in July and August. With the increase in population in Las Cruces and possibly influenced by global warming trends, both the humidity and ambient temperatures are slowly increasing. Homes are heated predominately with natural gas in incorporated areas and propane outside of them. The most common heating systems are forced air systems without return-ducts and wall-mounted heaters.
The most common cooling systems are evaporative (swamp) coolers, but the use of refrigerated air (air conditioning) is becoming more common. These systems usually use the same ductwork as the furnace uses in the winter. The ductwork is usually located in the ceiling or attic where it is subjected to extremes of temperature and where air leakage from the pressurized ductwork is lost from the building “envelope.” 20% loss of heating and cooling is not uncommon with these systems.
Evaporative coolers commonly use over 10,000 gallons of water yearly and require at least twice-yearly maintenance because of the sediments and salts left after the water has evaporated. Pads have to be replaced and the units themselves have a limited service life. Moderately large houses of 2400 sq ft typically require two coolers.
Refrigerated air systems, a.k.a. air conditioning, require less maintenance but have a higher initial cost, typically $4000-$10000, and much higher energy costs, usually $300-$800 more per year on a moderately large house. However, electric generating stations consume a great deal of water, the additional use of which is invisible to the refrigerated air consumer while contributing to global warming.
The square footage cost was high compared to homes in this area, but that was due to high-quality stucco, roofing, insulation, and other features that have saved money over time.”
Elevation 3850 to 4500 ft
32°19’ N Latitude
Winter Design Temp 20F
Extreme Low Temperature 10F
Heating Degree Days/year ca 4000
New York City ~ 7000
Minneapolis ~ 10000
Summer Design Temp 97F
Extreme High Temperature 112F
Cooling Degree Days/year ca 1000
Daily temperature range 26F
Average Cloudy Days/year 9
Clear Day Solar Energy Available in January: 1900 BTU/Square Foot/Day (A BTU is approximately the heat released by a burning wooden matchstick)
Radiant Heating and Cooling
We always integrate the domestic hot water system with an active solar space heater. Then the system can produce savings 12 months a year. In this area domestic hot water heating requires as much energy as space heating.
Radiant Heating and Cooling can also be called hydronic heating and cooling because it uses water as the heat transfer medium instead of air. It can be called radiant because the majority of heating and cooling transfer in a home is actually through infrared radiation.
To illustrate why it is better to heat or cool with water imagine that you have 2 similar cups in front of you. One of the cups has air at 72 Degrees F and the other cup has water at the same temperature. If you accidentally burn your finger, which cup would you put it into? Correct, the cup with water in it, because water holds 3,500 time as much heat as an equal volume of air. This superior heat holding ability allows much more efficient transfer or storage of heat with water, uses relatively small diameter tubing, and its operation is virtually silent. Heat transfer with air requires 20 times as much power, requires much larger ducts, and is often noisy. A typical hydronic tube has a cross section of less than ½ square inch while a typical forced air duct is 200 square inches. Below is an aerial picture of the hydronic tubing in the floor of a 5,000 square foot building. The heating required in this building is distributed by a pump that uses less than 45 watts!
Radiant (Hydronic) Heating and Cooling System So what does this mean for the comfort and economy of a building?
In contrast to forced air heating, it is more comfortable, silent, draft free, clean, allows zone controlling of conditioned areas, and is much more energy efficient.
The main disadvantage of radiant heating is that it has usually been assumed that a separate system of ductwork would be required for cooling. With the availability of modern materials and technology this is no longer true. Duct work is not required for cooling but in some climates may be needed for humidity control.
Hydronic Radiant Cooling
We have an amazing new adaptation of a very old technology that is just perfect for cooling buildings in the arid Southwest climate. It provides such superior comfort and performance as to be difficult to describe.
_Up to 80% energy savings
-A greater comfort range.
-Operates in almost total silence.
-No adverse humidity effects.
-Greater Design Freedom.
-Almost no visible components.
-Easy Zone control.
-No Mold concerns.
-Great environmental benefits.
The term for it is hydronic radiant panel cooling, because it uses water instead of air to transport heat and, and it is accurate to call it radiant cooling, because the majority of the heat is removed from the building through radiant transfer from the occupants and other building loads to panels inherent and integral to the building, either the ceiling, walls, or floor.
We are accustomed to using fan forced air almost exclusively in the US for cooling, radiant is much more common in Europe. The Bank of England, built in the 19th century had radiant cooling. Water can carry 3500 times as much heat as an equal volume of air, with the energy cost for transport of heating and cooling 20 times as great in an air system as in a hydronic system.
If you have ever experienced the benefits of radiant heating versus forced air heating, then you have some idea of the difference between radiant cooling versus forced air-cooling. In a large building with conventional air-conditioning, 20% of the occupants are uncomfortable at any one time. You can understand why radiant cooling has become so popular in superior quality construction in Europe.
With radiant cooling you can take free cooling from the desert night skies and store it in the thermal mass of the building, providing dependable, super-efficient temperature control. Animals, native to the desert, store the cool of the desert night in their burrows. By taking advantage of the thermal mass inherent in buildings and cooling them between sunset and sunrise we can act like natives instead of fighting entropy and struggling to cool ourselves by pumping heat out of the building at the hottest part of the day. Almost all buildings in the Southwest are built with concrete floors that can be readily used for heat, or cool storage. Thermal mass for cooling works even better than it does for heating, as in solar design, because, while you may sometimes have days without sunshine, you never have nights without darkness.
The total amount of cooling will depend on the dew point outside and the temperature of the water going to the cooler. In some buildings and climates there will be a need for supplemental refrigerative cooling, but the same thermal storage strategy will provide considerable energy savings. The energy costs for the operation of the systems described above is only about 10-30% of that of a conventional refrigeration system and with proper design provides similar energy savings in most climates.
Benefits to the local and global climate are very large. Besides using so much more electricity, refrigerated air conditioning heats and dries the immediate environment. For example, the current summer temperature in Phoenix is 20 degrees higher than it was historically, and most of that change has come about since the introduction of refrigerated air-conditioning to the area. Refrigerated air-conditioning pumps heat from the inside of a building to the outside, plus the waste heat. The fans alone account for about 30% of that waste heat generated. A hydronic system only uses 1/20th as much power for the same function. Compared to a conventional AC system, a hydronic radiant cooling system can save 114 gallons of water, reduce local heating by 683,000 BTU, and reduce carbon dioxide emissions by 338 lbs a day for a typical size house in the Las Cruces area.
In areas that are more favorable, where there is no need for dehumidification or supplemental cooling the payback period is minimal, and the savings impressive, but the most important aspect may be the superior quality of the interior environment.