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Snowmelt slab sensor

RPK
RPK Member Posts: 95
Can anyone recommend a snowmelt slab sensor that can report slab temperature and surface moisture directly to a building automation system?  I like the heat timer and Tekmar sensors, but they have to be used with matching controllers.  Tekmar does make a device that connects to the slab sensor and reports to BAS via BACnet.  This is for a hospital ambulance area.  The current design utilizes an ETI slab sensor that senses temp and moisture but only provides a contact closure output (temperature and moisture setpoints are fixed) paired with a thermistor “glued” to the side of the slab sensor.”  Needless to say, affixing any old themistor to the side of the slab sensor, burying it in concrete and and trying to keep the terminations clean and dry sounds like a bad idea.   I have actually seen the Tekmar connected directly to a BAS, but Tekmar’s literature actually contains a disclaimer stating that using the sensor in this manner voids the warranty.  One nice thing about the Tekmar and heat timer sensors is that they come with nice length of  direct burial cable factory installed, so no terminations required under the slab.  

Comments

  • Zman
    Zman Member Posts: 7,435
    Trying to manage a Tekmar sensor like the 090 directly with a DDC system is problematic. You can read the slab temp and conductivity across the surface pretty easily. Where you get into trouble is the heater and heater sensor. The way those work together is a Tekmar trade secret. I have seen guys try to integrate directly, but have never seen one work right.

    The good news is that Tekmar has a solution. https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/176333-source/pf-t-681/pf-t-681 or https://www.watts.com/products/hvac-hot-water-solutions/controls/snow-melting-controls/680/680

    I have the 680 installed on several projects and they work great. I did not do the DDC integration, but the control guys that did rave about it (and DDC guys rarely have nice things to say about Tekmar :* )
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • RPK
    RPK Member Posts: 95
    Thanks ZMan! I have only used a Tekmar snowmelt controller once, but it worked really well and seemed a little more flexible than the Heat Timer.  Now I’m really curious about how the directly integrated Tekmar sensors I know of are being handled.  There are 3 that I know of at a school district, that have been working wonderfully for the past couple years.  As far as the current job goes,  my most trusted DDC contractor tells me that their preferred method involves a thermpwell epoxied to the housing of the ETI snowmelt
    sensor and assures me that it works quite well.  
  • hot_rod
    hot_rod Member Posts: 18,254
    HBX is the other player,

    https://hbxcontrols.com/sno-0110.php
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Zman
  • RPK
    RPK Member Posts: 95
    Thanks HotRod.  Any experience with the HBX?  
  • hot_rod
    hot_rod Member Posts: 18,254
    RPK said:
    Thanks HotRod.  Any experience with the HBX?  
    Just from the HBX folks😉
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream