Installing SlabHeat

Installing SlabHeat^™.

The spacing of the SlabHeat cable will help determine how much heated area can be covered by a single SlabHeat coil. SlabHeat can be installed on either 4” (15 W/sf) or 6” (10 W/sf) centers, depending on the amount of heat required for the area. A heat loss calculation is required to know which spacing is right for the project. If the SlabHeat system is to be used for floor warming only, installing the cable at 6” on center is sufficient.

Another consideration to take into account when designing a SlabHeat system is to know the available amperage. A 120 VAC system will pull twice the amps as a 240 VAC system. If amp capacity is a factor, it may be better designing for 240 VAC. Make sure the voltage supplied matches the voltage requirement of the SlabHeat cable. Failure to do so may result in either an over-heating or under-heating condition.

SlabHeat can be installed in either a new slab pour or over an existing slab with a concrete cap. For new concrete pours, just zip-tie the cable to the rewire/rebar and elevate to the middle of the slab. If installing over an existing slab, it will be necessary to install CableStrap^™ to hold the SlabHeat cable in place.
When finished the only visible part to the system is the wall mounted SunStat thermostat.

A nice feature of the SlabHeat system is there is no annual maintenance required. Hydronic systems can require periodic cycling of the circulators to prevent the impellers from locking up during periods of non-use. Hydronic systems may also require fluid testing, treatment, and periodic system purges. SlabHeat systems are simple and easy.

Selecting the right product for the application is a breeze with SlabHeat. Since there are fewer parts needed to run a system, just thecable and control, ordering is easier than with a hydronic system. Just make sure to purchase the correct voltage, either 120 VAC or 240 VAC, and the correct number of thermostats or relays.

Controlling a SlabHeat system is also simple. Choose between two types of SunStat controls: programmable and non-programmable. Either one can be set up to respond to either a set floor or air temperature. SunStats are also dual voltage, meaning a single SunStat control can operate either a 120 VAC or 240 VAC system directly (one or the other, not both at the same time). This eliminates the need for cumbersome contactors, transformers, and complicated wiring as seen with other types of heating systems.

Whether heating a small sunroom or an entire warehouse, SlabHeat is the simple solution.

Christopher Campfield
Watts Radiant System Designer

Introducing SlabHeat

Introducing SlabHeat^™.

SlabHeat expands upon our successful electric floor warming product lines. Designed as a robust, job site resistant cable, SlabHeat is an electric radiant system installed directly in concrete. A combination of strength, durability, and simplicity lies at the heart of SlabHeat. Engineered to provide room heating as well as floor warming for a wide range of applications, SlabHeat is the perfect solution for even the toughest heating project.

Why choose SlabHeat over a traditional hydronic radiant system?

One of SlabHeat’s benefits is the lack of a complicated mechanical room. With SlabHeat there is no need for a heat source such as a boiler; the cable is the heat source! For new construction, as well as remodel, trying to add a dedicated heat source can create its own set of challenges. Hydronic heat sources require a dedicated space, venting, power, and fuel. Hard piping is also needed to circulate the heated water. SlabHeat has none of these obstacles. With SlabHeat all that is required is to run the cable across the space and connect to the SunStat^® thermostat. Then, simply pull dedicated 120 VAC or 240 VAC power to the area to be heated. When using a SunStat thermostat, the rest is as easy as wiring a light switch.

Designing a SlabHeat system is much simpler than designing a typical hydronic radiant system. First, figure the gross square footage (wall to wall), then multiply that number by 90%. This square footage will be your heated area. The area to be heated will help determine if a 120 VAC or a 240 VAC system should be used. For a 120 VAC system this is approximately 115 square feet of heated floor area at 4” on center. For a 240 VAC system this is about 225 square feet of heated floor area at 4” on center. This is determined by the SunStat 15 amp limit. If larger areas are to be heated one of two things need to happen. Either add additional SunStat thermostats (one for each additional 115 or 225 square feet of heated area) or add SunStat Relays to the control strategy (one Relay for each additional 115 or 225 square foot of heated area).

SunStat Relays are specifically designed to work with the SunStat thermostat. Each Relay wires back to the SunStat thermostat and acts as an extension of the thermostat. A total of ten Relays can be daisy-chained off of a single SunStat thermostat. Refer to the SlabHeat installation manual for further details on setting up the SunStat or SunStat Relays.

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Christopher Campfield
Watts Radiant System Designer

Basic Design of Hydronic Freezer Panel Systems

Description:
A typical freezer application consists of an industrial sized, permanent freezer above a soil or compacted base. One issue resulting from this application involves the ground directly below the freezer heaving due to the moisture in the soil freezing. This heaving can sacrifice the integrity of the structure and should be avoided or mitigated if possible.

Solution:
To remedy the freezing and subsequent heaving of the soil, circulate hot water through piping in the soil to maintain a temperature above freezing. The ideal solution is to heat the soil enough to prevent freezing, while not causing excessive heat to transfer to the freezer itself, reducing efficiency and increasing load on the mechanical systems.

Design:
The design for the necessary supply fluid temperature is extrapolated from ASHRAE heating load calculations. The output of the surface of the soil is dependent on the freezer design. Freezers with internal temperature ranges between 20 °F and 30 °F are designed with loads of 3 BTU/h-ft², the ambient temperature is set at 50 °F directly above the soil, with a maximum ground surface temperature of 55 °F. These assumptions yield a solution that results in the soil staying above freezing (32 °F), while limiting the surface temperature of the soil as to minimize the negative effects on the freezer mechanical system. As we are not concerned with striping or stratification on the surface, as we would be in a standard heating application, designs are computed around 36” or 48” tube spacing. NOTE: The diameter and length of the tubing are irrelevant when determining a supply fluid temperature and should be selected to optimize cost, availability, and mechanical room and pumping solutions.

Results:
Empirical data shows that the resulting supply fluid temperatures within temperate climates range from 60 °F to 65 °F. With supply fluid temperatures that range close to the ground temperature, the back and edge losses from the soil are negligible. Dozens of these systems have been designed by Watts Radiant and are performing as expected for many years. The best results have been realized when combining intelligent controls that monitor ground temperatures with a heat source that harvests the waste heat produced from the freezer system. By doing this, a hydronic freeze protection system can be an attractive, simple solution that can be run with minimal cost to the owner.

-MDR

Sludge in Radiant Systems

Black sludge and other debris is often the initial sign of trouble for a hydronic system. Left untreated, corrosion will drastically shorten the life of any hydronic heating system. But how is corrosion treated? To answer this question it is important to understand what corrosion is and how it is caused. Different types of corrosion will require different types of treatment.

The most common cause is basic oxidation, or rust. Oxidation happens when oxygen, which is entrained in the water, reacts with ferrous (iron based) components. The rate in oxidation is doubled with every 18 degree rise in water temperature. Being a closed-loop radiant system, the internal water generally operates in the 100°-140°F range. Even a small amount of oxygen can cause significant corrosion. A simple field test can be used to visually verify corrosion. Partially fill a clear, clean glass with system fluid and then hold a magnet up to the side of the glass. Watch as the floating black particles migrate towards the magnate. This happens because the black particles are rust, composed mostly of iron, which is naturally attracted to the magnet.

Another fairly common cause for corrosion is an improperly balanced pH level. An ideal pH level is 7 on the pH scale, which is neither acidic nor basic. A low pH level will turn the system fluid acidic, causing the fluid to “eat away” at the ferrous components. Conversely, a high pH level is basic. Basic levels can be equally aggressive depending on the metals used. For the most part, basic pH levels do not adversely affect hydronic components themselves. Instead, a high, or alkaline, pH level tends to cause unwanted scale deposits. All the dissolved materials naturally present in the water supplied to the system will more likely precipitate out at higher pH levels, causing potential obstructions or reduced system performance over time. An example of a high pH system generally involves glycol. Most glycol based systems tend to start out more towards the basic pH range due to the inhibitors used.

The downside to glycol is the pH level is not constant and will drop as the glycol ages. Aging is a result of the glycol solution absorbing oxygen (which makes it an effective tool against oxygen permeation). A good practice to follow is to perform a yearly check of the glycol and re-fill with a new solution or add inhibitors when needed.

If the corrosion takes on the form of orange sludge, or has a pungent order, the system might be experiencing microbial growth. With water temperatures below 160 degrees, oxygen, and a food source such as glycol or sulfur rich water, microbial life can begin growing in the system. The resulting sludge is created when these microbes die. This is a particular problem with areas using artesian wells, which tend to be a good source of sulfur.

The last main cause for corrosion is electrolysis due to dissimilar metals. Because of all the trace metals present in city water, the possibility of these different metals reacting with each other and various system components is fairly significant. Metallics suspended in water create an excellent electrical conductor, increasing the chance of corrosion in systems with high ferrous content.

The best solution to any of these conditions is to ensure the system has been properly treated. To better evaluate the situation and determine which problems are causing the corrosion a fluid test should be performed. Companies which conduct these tests will be able to determine the nature and root-cause of the corrosion as well as offer a means of correction. Most “cures” include adding a specially formulated additive to the system. Although these additives will cure the current corrosion issues they won't eliminate the need for regular system maintenance and fluid checks. Inspect the hydronic system before the beginning of each heating season and take the necessary steps to ensure a corrosion-free season!

Christopher Campfield
Watts Radiant System Designer