The ability to extensively zone heating distribution has long been heralded as a major advantage of hydronic systems. At first, the concept appears so simple: Just install an electrically operated valve for each zone and open a given valve when its zone needs heat. Too often overlooked is the increased pressure differential across the circulator each time a zone valve closes. Left unchecked, high differential pressures can lead to flow noises, overheated pumps, flow leakage in other closed zone valves, and even erosion of piping materials.
The solution in small to medium size systems is to install a differential pressure bypass valve across the supply and return mains of the distribution system. In effect, this valve "caps" the upper differential pressure across the mains. On larger systems, circulator speed can be adjusted using a variable frequency drive VFD to maintain differential pressure within prescribed limits. In addition to regulating pressure, this approach reduces energy consumption of the pump under partial load conditions.
Look for variable speed distribution pumps to be available for smaller residential and light commercial applications in the near future. Use valves with equal percentage characteristics when controlling heat output by varying flow rate. The heat output from most hydronic emitters--be they baseboard, radiant floor circuits or air handlers--doesn't vary in proportion to the flow rate passing through them.
The graph in Fig. This implies that heat output control during part load conditions requires extremely small and precise changes in flow rate--a task that some throttling valves don't handle very well.
To counteract this non-linear characteristic, many manufacturers offer control valves with "equal percentage" characteristics. The plugs in these valves are shaped so that the gap between the plug and its seat opens very slowly as the stem begins to lift. The farther the stem lifts, the faster the gap between the plug and seat opens. A typical flow rate versus stem lift curve for an equal percentage valve is shown in Fig.
The curve is essentially the mirror image of the heat output versus flow rate curve for the heat emitter. When these two characteristics are paired together, the result is an approximately proportional relationship between heat output and stem lift. Don't 1. Don't forget to account for temperature drops along series connected loads. Whenever a stream of water gives up sensible heat, its temperature drops.
When several loads--be they individual heat emitters or complete secondary circuits--are connected in series along a common piping path, the temperature drop gT across each load should be calculated, and then used to determine the supply water temperature available to the downstream heat emitter.
Not doing so leads to undersized heat emitters near the end of the circuit. Don't 2. Don't route several independently pumped circuits through a common component having high flow resistance. The situation depicted in Fig. The bigger circulator is capable of setting up a large gP across the high flow resistance heat source.
The gP may even be higher than the shut-off head of the smaller circulator, preventing flow in the circuit it serves. The common header piping in a system employing parallel circulators should also be generously sized so that pressure variations along the headers are minimal as various circulators turn on and off. Don't 3. Don't use high head pumps on zone valve systems. Every time a zone valve closes, the system curve gets steeper, and its intersection with the pump curve moves higher.
Differential pressure across the pump increases. The "steeper" the pump curve, the greater the incremental rise in pressure as each zone valve closes. A high-head pump with a steep curve can create high velocity flow in piping when only one or two zones are operating. The high gP can even lift the plugs of zone valves that are supposed to be closed, causing heat migration into inactive zones. Circulators with flat pump curves are best for zone valve systems.
If you can't find a circulator with a suitable pump curve, consider pairing up a couple of small circulators in parallel. The curve representing the net performance of parallel circulators becomes increasingly flat as more circulators are added. Still another solution is a variable speed distribution circulator, as mentioned earlier. Don't 4. Don't short-cycle boilers by "microloading. The math adds up at design load conditions when all loads are presumed on. But, what happens when only one of those loads is calling for heat?
At HydronicHeating. Hydronic radiant heating fulfills that need and provides a smart residential heating alternative that will help lower your energy costs and impact on the environment. The articles below are designed to help you understand the benefits of this method of heating and answer any questions you might have. Home About Contact. What is Hydronic Heating? For those who are completely new to hydronics and would like to get an overview of why this type of heating system has become so popular over the last several years, this article will help you understand the advantages that radiant heat provides, and how your family can benefit from this modern energy efficient system.
How Does Hydronic Heating Work? The principles of how hydronic heat actually works are explained here. Heat transfer, especially when it comes to heating a home, can be completed in many ways. The two different types of wet application are for: Slab on grade foundations : During this process the radiant tubing is secured to the rebar or reinforcing structure within the slab before the wet concrete is poured into the foundation. Thin Slab: These are created on top of subfloor systems where the tubing is attached to the subfloor and a thin layer of self leveling concrete is poured over the top.
The bonus of this installation is that it allows second floor rooms, as well as areas above basements and crawlspaces to have radiant floors installed. Dry — Dry systems of radiant flooring installation, often called plate systems, utilize prebuilt panels that have tracks for the radiant tubing within their design.
This makes it easy for installers to loop the tubes as needed before covering with flooring material. Without the thermal mass provided by concrete, a dry installation method can require more careful placement of insulation and the addition of heat reflectors to help separate the heating zones and direct the warmth in the right direction.
Hydronic Radiator and Baseboard Installation Radiators and baseboard hydronic heaters are much simpler to install because there is far less piping to utilized overall. Site Navigation: What is Hydronic Heating?
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