Backup Heater For Radiant & Hydronic Heating System Variable Capacity Modulating Automatic Backup Heat For Air-To-Water Heat Pumps (Hydronic Heat Pumps)

The V18-B dynamically variable capacity inline (tankless) backup heater is designed for use with intelligent variable capacity hydronic (air-to-water) heat pumps such as the Chiltrix CX34. The V18-B variable capacity backup heater automatically adjusts its BTU (Watts) output to target an exact match to any shortfall of heating, in real time. The V18-B backup heater provides between 0 – 18,766 BTU, depending on the requirements of the moment.   Depending on your location, building envelope values, and other factors such as weather, you may need to consider an integrated backup heat solution. If backup heat is needed in your climate, the V18-B backup heater will save energy compared to the typical options, by providing only the amount of backup heating BTUs needed. As a fully integrated and automatic system, the V18-B also avoids the need for unsafe “portable” heaters, has a tiny footprint and little pressure drop. Consult with your Chiltrix sales engineer or HVAC professional to see if backup heat is needed for your application and location. The V18-B dynamically variable backup heater maximizes the percentage of compressor-generated high efficiency heat (COP ~2.5 to 3.5 or higher) and reduces the consumption of less efficient resistance backup heat (COP = 1.0).		Model V18 & V18-B Dynamically Variable Backup Heater Tankless In-Line Backup Heat Solution For Air-To-Water Heat Pumps Practically No Pressure Drop: @ 7 GPM = 0.000427775 ft. @ 14 GPM= 0.001438843 ft. V18-B Spec Sheet (After Nov 2019) V18 Specification Sheet (discontinued)

Compare to the Standard Air To Water Backup Heating Approach:

Prior to the introduction of the V18, the typical and globally-accepted standard backup heat solution for air-to-water (hydronic) heat pumps has been to mount a small electric water heater tank, with thermostat & element, in series on the supply side of the loop, to add extra heat when the heat pump cannot keep up with the load. In this example a controller enables the tank thermostat/heating element when loop temperature goals are not met. While this works and is the common global technique for hydronic backup heat, 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.

While providing capability to supply heat under conditions where the heat pump compressor cannot by itself handle the heating load, in the standard solution, comfort is acceptable but efficiency is lower than it could be due to temperature over-shoot. For example, when the tank-type backup heater overshoots, any extra heat provided (low-efficiency resistance heat) unnecessarily lowers the overall system efficiency by providing heat that could have been provided by the compressor at a much higher efficiency.

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, commercially available tankless heaters are not compatible with cold water running through them during the cooling season and as a result, they suffer condensation problems.

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

The patent-pending V18 & V18-B dynamically variable inline (tankless) backup heater solution avoids overshoot or undershoot issues by matching its output to a capacity shortage (BTU shortfall). For example, if a certain BTU is needed, a V18 targets exactly that amount of BTU. 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 output to match the load shortfall. The V18 is always targeting the precise amount of extra heat needed, allowing the compressor to provide the highest possible percentage of the heating requirement and providing stable heat values in the hydronic loop. So aside from not requiring the footprint/space needed for a backup tank and avoiding the excessive pressure drop and condensation issues of a tankless heater, the V18 saves a lot of energy by keeping the loop temperatures stable and allowing the compressor to provide the highest possible percentage of the heat.

The V18-B is essentially the same system as V18, but it does not need a stand-alone controller, it uses the onboard CX34 controls. For CX34 produced after Nov 2019.

The charts below illustrate the efficiency gain of a dynamically modulating inline heater compared to the standard tank approach.

Above: Ref. building with V18 backup heater. Click to expand and see more info.	Above: Ref building with standard tank backup heater. Click to expand and see more info.

Contact Us        V18-B Spec sheet       V18-B Manual

How Does The V18 Hydronic/Radiant Backup Heater Work?

The patent-pending V18 uses a special long-life and replaceable Incoloy resistance heating element rated at up to 5,500w (18,766 BTU, rated at 230v). Actual maximum watts/BTU output will vary according the 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 shortfall. The element output can be adjusted on the fly, for example at 55w (187 BTU) or 110w (375 BTU), and so forth up to the full power of 5500w (18,766 BTU) 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 amount of such shortfall. When controlled by the Chiltrix heat pump, the V18 can be targeted to match its output closely to any BTU 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 of 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 >/= 30a circuit with GFCI breaker, 208-240v. Multiple V18 units (up to 3) can be installed with a single heat pump if needed.

V18-B Spec sheet

V18 Specification Sheet (old version)

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PATENT PENDING

Below, partially assembled V18 backup heater kit mounted to painted plywood.
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