William AllenWilliam Allen, Ph.D., Associate Development Engineer and head of the WCEC Residential Radiant project 

Residential Radiant ceiling panel prototype. Designed by WCEC and tested in a Sacramento home

Residential Radiant chilled water storage tank to offset peak load demand. Designed by WCEC and tested in a Sacramento home  

Whether for environmental or monetary reasons, energy efficiency and reduced energy use concerns have permeated into the collective consciousness of most people. Today, most homes are outfitted with CFL light bulbs that use a fraction of the energy as yesterday’s incandescent lamps (many switching to an even lower energy-use LED lamp) and HVAC units with a SEER greater than 13 are much more commonplace. All of these energy efficient technologies are helping to reduce overall energy consumption, but most of these now ubiquitous products have only a marginal impact on peak load use.    

What is Peak Energy Demand?
Peak demand, or peak load use, is the 6 hour window typically between 2pm-8pm when the demand for cooling is highest. We leave the comfort of our offices, come home, turn on the lights and crank the thermostats in our homes to our desired temperature. This has a significant impact on our power grid and utility infrastructure that has to build and maintain inefficient, quick and dirty power stations just to meet this demand.

Click to enlarge

How Radiant Cooling Works
Radiant cooling works by actively chilling large surfaces in a space (usually either the floor or the ceiling). This allows them to absorb heat from surrounding surfaces, including the human body. Cooling is most often provided by cold water circulating in copper or PEX pipes. This type of cooling usually makes a room feel more consistently cool than a forced air system that may have cold spots near a vent. In a room with cool surfaces, people will tend to feel comfortable at a slightly higher thermostat setting than with a forced air system, thus saving energy. Radiant systems also aren’t susceptible to duct losses typical in most residential forced-air systems.

Click to enlarge

Peak-Load Shifting
A standard, forced-air system relies on the outdoor condenser to remove heat from the refrigerant. Unfortunately, at peak-demand hours, these systems are running at their least efficient because ambient outdoor-air temperatures are already so high, increasing power use on the system to remove the excess heat. A water-cooled condenser can help alleviate the inefficiencies of running a condenser during hot, peak hours reducing a typical HVAC’s system draw during peak by 30%-50%, but is nowhere near as substantial a peak-reduction as what can be obtained by radiant systems. With a chilled water storage tank, a radiant system can reduce peak-time demand energy use by 95%… using only a fraction of energy to move the water through the system and keep the sensors/thermostat on. Later on at night during off-peak hours, when the outdoor air temperature has dropped, the chilled water storage tank turns on its condenser to cool the water in the storage tank for the next day’s hot weather; dramatically reducing peak demand and increasing efficiency of condenser operation due to cooler ambient runtime temperatures.
WCEC’s own William Allen has been researching the use of radiant systems in residential applications for over 3 years now, looking into the economic and practical viability of this technology. His research implements 2 different radiant system designs in homes in Sacramento, including a chilled water storage tank for peak load shifting. The report also highlights the market challenges for new HVAC technology and proposes some solutions for these systems to gain a foothold in the greater HVAC marketplace. He is currently in the process of finalizing his findings for the CEC.

Q: What do you find most promising about radiant technology?
3 things:
1) The potential for energy savings is significant due to the elimination of duct losses typically found in standard forced air systems, and the fact that using water a heat transport medium saves energy due to low pump power rather than the relatively high power used by fans for blowing air.
2) A radiant system’s large active area cools or heats more evenly throughout a space, removing entirely the hot/cold spots typically found in forced air systems. This greatly increases occupant comfort levels.
3) The potential for load shifting through a chilled water storage system. This load shifting not only reduces peak demand load off the utilities, but it also increases efficiency gains due to the condenser running later at night, when ambient temperatures are much lower than during the peak demand hours. It can also allow the use of evaporative or hybrid cooling systems, which will also tend to run more efficiently during cooler night hours.  

Q: What was the main focus for this research project?
The main focus of the project is to investigate, design and implement a cost effective radiant system with peak load shifting for use in new build houses or as a retrofit. This effort required market research, including existing solutions, development of an integrated control system for heating/cooling and the development of a cost effective chilled water storage system. Traditionally, these types of storage systems are only cost effective for larger applications, so we set out to create something that could be economically viable on a smaller scale. 

Q: What challenges did you encounter?
The downturn in the housing market made it more difficult to find new-build test sites. Finding industrial partners for the storage elements and panels was also very difficult, again due to the market downturn, which led to manufacturers being reluctant to commit the R&D money to develop a product like this. This led to WCEC to design our own prototype panels which we predict would have an installed cost of less than $5/sqft, compared to the typical $12-$15 for existing systems. We have also worked with Uponor who are developing a panel designed for new build installation with a projected cost of less than $4/sqft.

Q: What are the next steps for radiant to become a more prevalent technology?
We need to do wider field demonstrations and work with utilities to add incentives for load shifting to bring down customer first costs, as well educating the public about the benefits of radiant systems.


Q: What should be the next technological challenge that WCEC should take on in order to further advance the implementation of radiant technology?
We need to work with a major player in the marketplace to develop a ‘plug and play’ control system, and turn-key radiant system solution. At the moment, radiant is treated as a custom install, and is therefore not part of the standard HVAC lexicon with builders, installers and contractors. Because of this, radiant systems are rarely recommended by builders because they simply do not know enough about radiant and don’t know many contractors willing to install these systems. This lack of awareness about these systems limits demand which keeps prices high and prevents cost reductions available due to economies of scale. If we can work together with builders and manufacturers to create more modular systems, radiant cooling could break out of the niche mold it has been in for 30+ years.