Tube Placement & Spacing

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Depending upon the electric rate requirements, off-peak rates, length of on-peak interrupt, etc.; tube placement and spacing needs to be a prime consideration. Electro Industries has various training tools or insulation guides relating to length of interrupt and ETS storage requirements. If needed, request assistance.



Typical Tubing Install - by far the most common installation technique. Very little storage (2-4 hours). Fairly quick temperature response time. Typically requires low water temperature, slab thermostat recommended.
BC016 Under-Slab Install, without board insulation - if the peripheral insulation is in place and high priority, there is minimal requirement for the insulation under concrete. This illustration is just as efficient and just as effective. Plus this illustration provides more earth storage and can be used with off-peak storage rates. Often the justification for the insulation board is "a place to fasten the tube". The reduced labor for walk around staple gun may justify the insulation board. However, realize installing insulation board destroys earth storage and if off-peak storage rates are to be applied (now or in the future) see below - ETS Radiant Storage techniques.
BC014 Sub-Floor Install - additions, remodeling, and whole home applications. Virtually no storage capability. Very quick response time. Typically requires low water temperature and multiple zones. In order to prevent floor overheat and maintain low water temperature, recommend EMB-W-9 or EB-S=** series boilers. Air or slab thermostat is okay. New Electro digital is ideal.
BC015 Under-Floor Install - use manufacturer's recommendations and installation technique. Diagram is typical in illustration, emphasizing the important components and basic placement. This is not as effective or as efficient as BC014 and requires considerably higher water temperatures. Recommend EB-WX-** series boiler with outdoor reset.

ETS Radiant Storage

When we think of ETS (Earth Thermal Storage), our first thought doesn't necessarily go to hydronic systems. Over several decades, heating systems have used the earth to store heat based on a lowest-cost electric (off-peak) rate. With the popularity of using hydronic tubing as the preferred method of new construction heating, why not heat the water using your electric utility's off-peak rate? Combining an electric boiler and burying the tubing in a bed of sand can provide a very economical primary heating source.

The diagrams shown below can give you a better feel for how to install tubing specifically for your utility control program. Whether your utility offers a 4-8-16 hour control strategy, a system designed properly can provide 24-hour a day comfort with interruptible electric power.

BC011 ETS Storage Install - most economical form of heat, lower levels, slab on grade applications. Works well with longer control stratedy. Slow response time. Typically requires low water temperatures. Slab thermostat is necessary and required.
BC012 ETS Storage Install - same as BC011 except more sand for longer off-peak interrupts.
BC013 Floating Slab Install- there are various techniques used, this illustration simply shows the basic requirements. By using a sand bed installation is simpler and provides the storage without affecting annual efficiency or comfort.

Note: Common to all diagrams is the barrier between the slab and foundation or outside block wall. This is very important to prevent the slab from conducting directly to the outside.

Vapor barrier is optional, Electro Industries always recommends because we've seen problems with too much moisture coming through the floor. However, the insulation board may be adequate in many areas.

The peripheral insulation is significantly more important than the insulation under the slab. The key factor is keeping the heat energy from escaping horizontally. Heat energy will not go down more than about 18" to 24" and becomes stable at that point.

Slab thermostats can be added at any time using Electro Industries' electronic sensor. Sensor can easily be drilled in with a 1/4" hole at a surface sensing point.

Reference sand bed technique, the domestic plumbing and drain system can actually be in the sand above the tube/insulation board. Often this simplifies the basic plumbing task and allows simpler concrete installation techniques.

Tube Spacing

The rule of thumb and most common installation is 12" on centers, with perhaps the outside first row or two being closer. This is adequate for basic heating and basic heat loss requirements.

However, in the case of ETS storage (again depending upon the charge time versus storage time) the heating source needs to be oversized by a factor of 1.2 to 1.5 to make sure the energy can be "pumped into" the storage bed during the shorter off-peak hours. If this is the case spacing also needs to apply to the multiplier. In many cases 12" spacing just simply will not provide enough tubing surface area to "pump in" the required energy during a typical 12-hour charge time. Electro Industries recommends 9" spacing or the installer go through the actual calculations to make sure the tubing can indeed produce adequate square foot Btu's for the storage recharge requirement.


Electro Industries, Inc., 2150 West River Street, PO Box 538, Monticello, MN 55362 (Map)
Phone: 800.922.4138 or 763.295.4138  Fax: 763.295.4434

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