V18-B

Compare to the Standard Air-to-Water Backup Heating Approach:

The typical and globally accepted standard backup heat solution for air-to-water (hydronic) heat pumps has been to add one or more electric water heater elements into an inline or buffer tank, to add extra heat when the heat pump cannot keep up with the load. When the heat pump cannot keep up, the elements start working, cycling on/off according to a thermostat. This is the way the entire industry does it. Except for Chiltrix. While this method provides backup heat, it is grossly inefficient by comparison to a V18.

Importantly, an electric backup resistance heat source has a COP 1.0, thus dragging down the system average COP when the heat pump and backup are both running. That’s bad enough, but when heat gets added to the buffer tank, the variable speed heat pump controller sees this as a reduction in load and slows down, causing a recursive need for more backup. Eventually, the backup becomes the primary. The heat pump may cycle off entirely.  Further thermal lag in the backup heat tank and hysteresis of the element/thermostat generally cause significant overshoot and undershoot of the temperature settings, with swings of up to 10 ºF above or below the target being common. Modulating tankless heaters have also been tested for radiant and hydronic backup applications but severe pressure-drop issues have proven them to be an undesirable alternative. Further, most of the available tankless heaters are not compatible with cold water running through them during the cooling season and as a result, they suffer condensation problems. These are the problems experienced with our competitors’ backup solutions.

What’s New & Different About The V18 Variable Backup Heater?

The unique, exclusive, and patented V18 fully solves the problems. The Chiltrix V18B is a dynamically variable inline (tankless) backup heater solution that avoids overshoot or undershoot issues by precisely matching its output to any capacity shortage (BTU/h shortfall). For example, if a certain BTU/h is needed, a V18 targets exactly that amount of BTU/h. The V18 can dynamically adjust its output in real time. As the load changes, and heating shortfall changes, the V18 changes with it dynamically, reconfiguring its BTU/h output to match the load shortfall. The V18 is always targeting the precise amount of extra heat needed, allowing the compressor, which is the more efficient heat source, to stay at full speed and provide the highest possible percentage of the heating.

The Chiltrix heat pump unit itself is a smart, patented, “load-aware” unit – it continually monitors its inlet and outlet temperatures, it knows the flow rate, and therefore, it always knows the exact BTU/h of load. If the Chiltrix heat pump cannot meet the load, it knows in real time exactly how many BTU/h it is short and commands the V18 to output that exact amount of power. The Chiltrix compressor is still performing all it can do, and does not slow down, the V18 incrementally injects any missing heat that’s needed. The charts below illustrate the efficiency gain of a dynamically modulating inline heater compared to the standard tank approach. The improvements are understated, giving maximum benefit of the doubt to the standard method.

How Does The V18 Hydronic/Radiant Backup Heater Work?

The patented Chiltrix V18 uses a special long-life and replaceable Incoloy resistance heating element rated at up to 5,500w (18,766 BTU/h, rated at 230v). Actual maximum watts/BTU/h output will vary according to the actual line voltage of the installation location which may be from 208v-240v. The element is installed in a linear configuration inside a 2″ stainless steel tube with 2″ NPT female threaded connections on each end. The tube is heavily insulated and wrapped by a stainless-steel outer cover. A special solid state relay controller is used to vary the watts of the element from 0w to 5500w in increments of 1%. The solid-state relay is controlled by information from the heat pump to accurately target the BTU/h shortfall. The element output can be adjusted on the fly, for example at 55w (187 BTU/h) or 110w (375 BTU/h), and so forth up to the full power of 5500w (18,766 BTU/h) as needed to match the requirement. The Chiltrix heat pump, which is a variable capacity unit, modulates its capacity based on continuously recalculating and adjusting its output to match the load. In this control process, the Chiltrix unit is also aware of any heating shortfall and knows the BTU/h amount of such shortfall. When controlled by the Chiltrix heat pump, the V18 can be targeted to match its output closely to any BTU/h shortfall in real time.

In all heat pump systems including Chiltrix, ultimately the “return” water temperature (or buffer tank temperature) directly or indirectly generates a call for a capacity increase or decrease. If a backup heater overshoots its target as is common with the standard tank approach, return water is at that time artificially higher, causing the heat pump to think the load has decreased, causing the heat pump to slow or stop. This action recursively creates the need for more backup heat and ultimately means a much higher than needed percentage of heat comes from the low efficiency backup unit than would be used if overshoot did not occur.

The V18 dynamically modulating heater eliminates this problem by avoiding overshoot. This allows the higher efficiency heat source (the compressor) to provide a much larger percentage of total heat during this time and minimizes the amount of lower efficiency resistance heat applied by the backup source which raises the average system COP significantly.

Installation & Safety

The V18 heater has a small footprint in a compact tubular form factor ~19″ in length and ~6″ in diameter and is connected to a small low voltage control unit measuring approximately 5″ x 5″ x 1.5″. The design of the V18 is such that it cannot operate if there is no heating shortfall, if outdoor temperature is above a predefined setting, if water flow is below a minimum GPM required, or if the water temperature (or the unit itself) rises above a maximum set point. Low voltage controls in communication with the Chiltrix heat pump send power modulation signals to the solid-state relay. Within the V18 there is a thermal overload safety switch that will interrupt power to the backup heater and must be manually reset if a maximum backup heater internal temperature is reached. The Incoloy heating element, the solid-state relay, and the thermal over-limit switch are all UL Listed. The V18 is shipped as a kit. Assembly and installation by a qualified and licensed installation professional is required.

Each V18 requires >/= 30 A circuit with GFCI breaker, 208-240v.