ASHRAE Journal - February 2012 - 30

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Outside

Inside

Heat Storage

Boiler

Collectors Solar Thermal Collector Primary Loop Primary Pump Secondary Loops Tempering Valve Pump Glycol Side Ice Melt Zones Heat Exchanger Water Side (Boiler Fluid)

DHW

Non-Mass Zones

Solar Loop Outdoor Pool and/or Spa Indoor Pool and/ or Spa Mass Zones

Domestic Hot Water Out Tempering Valve

Figure 2: Dual primary loop system block diagram.
Water Storage Tank Domestic Water Supply

Boiler (Backup Heat) Hot Water Pump
In-Tank Heat Exchanger

Floor Boiler Pump Pump

heat, preheat or no heat to any other device mounted on the primary loop. Each component can be added or deleted, during initial installation or at any time in the future using a two-pipe connection to the primary loop. Modular pump stations can be used with this two-pipe standard to speed up assembly on the job. Using this modular conﬁguration for pipe connections also allows for modular controls. Both the components and the controls can then plug and play together.

Foam Insulation Under Radiant Slab

Solar Heat Storage in Masonry Floors
Direct active solar heating of masonry warm ﬂoors has been done in our region dating back at least to the 1950s.2 This technique has enjoyed renewed popularity in recent years, thanks to the widespread use of PEX tubing in concrete radiant heated ﬂoors. The idea is to pump heat directly from a solar heat collector into the heat storage capacity of a masonry ﬂoor. The ﬂoor warms up slowly and stays warm well into the evening on cold sunny days. The challenge is to size the collectors and tilt them so that the ﬂoor is provided with a quantity of heat that does not cause overheating at any time of the year. This has a lot to do with the speciﬁc heat storage capacity of the masonry material in the ﬂoor, which has about one-half to one-third of the heat storage capacity of the same volume of water. Fortunately, there is an enormous volume in the radiant mass ﬂoors in a typical home construction, capable of storing about ﬁve times as much heat as a properly sized heat-storage water tank system. Another way of saying this is that the masonry warm ﬂoors will operate with temperature ﬂuctuations about ﬁve times lower than a typical water tank heat-storage system (when solar heated directly using common design strategies). This puts the ﬂoor temperature within the range of human comfort, and the lower temperatures result in lower rates of heat loss and higher thermal efﬁciency. This temperature performance has been observed and conﬁrmed in many ﬁeld installations. By some estimates, a 25% bonus can be realized in fuel savings by bypassing the storage tanks and heat exchangers whenever possible. If you take this into account and control the heat in the ﬂoor within the comfort range, you realize that you can often elimiashrae.org February 2012

Figure 1: Primary loop flow center. placed before the radiant ﬂoor tees, and swimming pool heat should be taken after the radiant ﬂoor connection.

Dual Primary Loop Heat Exchanger System
Figure 2 shows a block diagram of what has become our standard plumbing conﬁguration for solar combisystems in recent years. It provides all the pipe connections to deliver comprehensive solar hydronic heating to even our larger building projects and solar retroﬁts (typically up to 10,000 ft2 [929 m2]). The piping connections are divided into the outdoor components using glycol, and the indoor components using water as boiler ﬂuid. A primary heat exchanger provides a thermal pathway to deliver heat into or out of the building as required by the control system. The proper thermal sequencing is shown on the diagram in the order that the components are placed around the primary loop. In projects where some of the components are not included, or will be added later, the tees can be included, deleted or capped to match the needs of the job.

Primary Loop Configuration Provides Plug & Play Design
The piping conﬁguration seen in Figure 2 provides everything on our wish list mentioned earlier. Any heat source may be connected to any load or bypassed easily by the control system by simply turning secondary circulators (and zone valves) on or off. Any heating component can provide direct
30 ASHRAE Journal

ASHRAE Journal - February 2012

Table of Contents for the Digital Edition of ASHRAE Journal - February 2012