Radiant Loop Layout Patterns
By MIKE MILLERHeating Hydronics
A review of radiant loop layout patterns with their differences, as they best represent the heat distribution into spaces with different heat loss characteristics.
There are four most common loop layout options when dealing with an over pour installation. These are referred to as single-wall serpentine, double-wall serpentine, triple-wall serpentine and counter flow (as shown in Figures A-D). Depending on the application, any one of these should be applied in order to maximize the radiant systems efficiency and heat distribution effectiveness.
The single-wall serpentine pattern is commonly applied when only a single exterior wall represents the majority of the heat loss of a room. The warmest water is sent to the perimeter of the outside wall first and returned at six in. on centre (OC) for the first four runs (two in each direction) before the spacing can be widened to nine in. or beyond. For all future references, it is my personal preference to not have greater spacing than nine in. OC in any liveable space that would be enjoyed with bare feet.
Applied when two adjacent exterior walls represent the majority of the heat loss of a room, a double-wall serpentine pattern results in the warmest water being sent to the perimeter of the two outside walls first and returned at six in. OC for the first four runs (two in each direction) before the spacing can be widened to nine in. or beyond. The loop layout would continue with this pattern until completion.
A triple-wall serpentine pattern is applied when three adjacent exterior walls represent the majority of the heat loss of a room. The warmest water is sent around the perimeter of the three outside walls first and returned at six in. OC for the first four runs (two in each direction) before the spacing can be widened to nine inches or beyond. The loop layout would continue with this pattern until completion.
When the heat loss of the room is evenly distributed and/or no outside walls exist counter flow is the appropriate pattern. The warmest water is sent around the perimeter of the room first and spiralled at 12 or 18 ft. OC to the centre of the room before being returned at halfway in between in parallel runs, finishing off the loop at equal spacing throughout.
If the initial loop centre spacing was at 18 ft. OC prior to returning from the centre, the tubing would end up at nine in. OC when completed throughout the space.
There is no such thing as having too much tubing in a slab. The more tubing is installed, the lower the water temperature to heat the space. Having said that, tube spacing can be considered when designing a system in order to keep the number of mixed water temperatures required to a minimum. Should the heat load room by room end up with water temperature requirement spreads greater than 20F (-6.7C), adjusting the OC loop spacing in some areas could bring those water temperature needs within the whole system closer together. Most radiant manufacturers use this practice in order to design the most efficient systems possible, while keeping the end result most cost-effective. <>