Hi All I have a closed loop radiant heating system and i have read a little about turning it into a radiant cooling system in the summer. I have a well and the water coming out of it is 55 degrees. can some one help explain to me in more detail than I have read on how I would go about making my system cool in the summer. I live in Northern Maine so I usually dont need a lot of cooling. thanks Larry

The issue with radiant cooling systems in most climates is dehumidification - humidity needs to be kept low enough that you don't get mold - even in places like under the rug on a radiant floor.

On the other hand, making the floor a few degrees cooler can sometimes be OK (ie, susceptible places remain above mold inducing humidity levels) and helps with both air temperature and mean radiant temperature (ie, will make you more comfortable). Mold won't grow in places that dry out daily.

The most common myths about HR floor cooling are that it will cause condensation/mold and that you will have uncomfortable cold floors. To understand how to successfully accomplish HR floor cooling you first need to understand the difference between latent and sensible heat transfer, understand how to keep the floor surface temperature slightly warmer than the dew temperature point and understand how cooling comfort is actually achieved.

Cooling comfort is achieved when your body loses more heat than it is generating. To achieve cooling comfort we only need to lower the interior thermal mass temperature of the building to be a few degrees cooler than our skin temperature. This achieves the same sensation that you feel when you walk into a cool basement on a hot day. A person at rest loses about 62% of their heat via radiation when the interior mass temperature is a few degrees cooler than than their skin temperature (reference ASHRAE Fundamentals Handbook).

The aforementioned radiation heat loss is accomplished entirely by sensible heat transfer. Sensible heat transfer is heat transfer without changing the moisture content of the air. What you need to avoid is having the interior thermal mass surface absorb the heat that is being held by the moisture content in the air (i.e., the relative humidity of the air). This type of heat transfer is latent heat transfer. To avoid having latent heat transfer and resulting condensation on the floor, you have to keep the floor temperature warmer than the dew point temperature. For many climates, the dew point temperature is naturally much cooler than our skin temperature. The actual dew point temperature depends on the dry bulb temperature and relative humidity (or the wet bulb temperature) in a very predictable manner that can be precisely determined by using our psychrometrics software:

Borst Psychrometrics Software

A good example of the engineering procedure and the math required to successfully accomplish HR floor cooling may be found here:

Healthyheating.com

So HR floor cooling is typically successfully accomplished with some combination of dehumidification and the use of either a dedicated chiller or dedicated heat exchanger to an environmental lower temperature source that will enable cooling the floor temperature to about 2-3 degrees warmer than the dew point temperature. We often use Programmable Logic Controllers (PLCs) as our building HVAC controller (e.g., Allen-Bradley Micro 800) for our integrated HR floor heating and passive solar heating designs which also facilitates precise real time determination of the actual dew point temperature to enable successfully accomplishing HR floor cooling too. Here's a discussion about PLCs from about two years ago:

PID Control & Sensor System for Modular Configurations

I should also mention that if you have a low humidity diurnal temperature summer climate like we do in southern Oregon, you can easily keep low occupancy residential buildings very comfortable by just having a well insulated and well sealed building envelope that incorporates adequate interior thermal mass by just minimizing ventilation during the hot hours and maximizing ventilation during the cold hours.

Another reason is radiant heating has been around longer, and we understand it. We are familiar with radiators and baseboard heating. Those appliances are not designed for cooling. You need to understand it procedure of its working. Learn more about here

In our new house build we will be cooling the floors, but the water will first go through a fan coil in each room to do the dehumidification.

We are planning on using the fan on the fan coil to quickly heat or cool the air in the room and then the water will travel down stream and through the floors to maintain the room temp by getting the floor mass to the right temp.

Search "fan coil" if you are not sure what they are.

Balance (between dehumidification and cooling) could be an issue - water has to be pretty cold for dehumidification where water going to a radiant floor should be relatively warm (or you will get excessive sensible cooling, then flow will stop and then you will have no dehumidification). Fan coils only is likely to be a better balance (with a single water source).

Consider DOAS - use the ventilation air to reduce humidity and any sensible load can be handled by the radiant system. Only one fan coil needed. Works best if the building is very slightly positive pressurized (which is also good for your walls) or very tight.

Radiant ceilings and walls have some advantages (no rugs, convection is in the right direction) for radiant cooling.