Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
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Our best advice:

To prevent the unnecessary destruction of equipment efficiency and to optimize your indoor climate dollars, we recommend clients contact us for assistance during or prior to concept develop stages. At this point in the construction process we can still help you achieve high performance benchmark status for your project by suggesting concepts and executing design calculations and drafting services for inclusion in your architectural and construction tendering package.

Once clients have gone beyond concept and have engaged an architect and drafts person to begin construction docuements it is often too late.

As we like to say, "Begin with the End in Mind"

Forensic Services: For additional support visit our visitor services page.

Many of the inquires we receive are for troubleshooting issues which could have been prevented in the early stages of design.

Often these events are due to lack of research, mistakes, ignorance and ignoring basic fundamentals often in the pursuit of lowering costs or expediting project timelines.

Below is one example of a recently completed forensic study. In this case the dollar cost was not the leading cause but rather a hindsight requirement for sound attenuation between radiant conditioned floors on a LEED(TM) for Home renovation project (names and location removed for confidentiality).
 

Background:

  1. Client contracted with original service provider for a radiant floor heating system and subsequently required sound attenuation between floor levels adding to the overall flooring resistance.

  2. Project scope restricted to: Analyze modified radiant floor for performance and provide comments.

  3. Forensic models based on values from printouts done by others (CHC Certified Designer) dated month, day, year.

  4. Forensic models based on information provided by client via phone call on  month, day, year.

Conclusions:

  1. A finite element analysis (FEA) of the proposed modifications to the floor from the original assumptions used in the Sept 26th, 2011 printout show a floor capable of delivering the design flux (output) but only with considerable increases to the fluid temperatures (see concerns below).

  2. The values of the FEA study were checked against Figure 9. Design Graph for Sensible Heating and Cooling with Floor and Ceiling Panels from the 2008 ASHRAE HVAC Systems & Equipment, Chapter 6, Panel Heating and Cooling – values were congruent.

  3. At design loads of appx. 22 Btuh/ft2 flux typical of some areas on the main floor, the revised fluid temperature would now be estimated at appx. 160F average temperatures where as other main floor areas with loads approaching 30 Btuh/ft2 would require appx. 188F average temperatures.

  4. The basement was not evaluated. Zones selected for review were cursory based on representative surface and fluid temperatures.

  5. A zone by zone review was not performed. Should the system remain as planned to provide space heating, it is our opinion the change in floor R-value is substantive as such a new system design would be required. This could be performed by the original certified designer using the new information.

  6. These estimated temperatures are at maximum design conditions. While not evaluated in detail, it is also estimated that even at moderate winter loads the return temperature through a high efficiency boiler would likely be too high to take advantage of condensing technologies (requiring 136F or lower to deliver on maximum boiler performance).

  7. A more thorough BIN study of CWEC files for location would have to be performed to estimate hours of condensing versus non-condensing.

Concerns:

  1. Thermal suppression effects from beds, couches other large floor furnishings – due to the borderline performance this effect cannot be ignored.

  2. Thermal suppression effects from throw rugs if placed on floor - due to the borderline performance this effect cannot be ignored.

  3. Time lag effects from floor mass of 1.5” topping plus ” sub floor + ” hardwood + ” rubber (can be mitigated with reset controls).

  4. Expansion rate of freely suspended (not encased) PEX pipe due to larger differential temperatures (i.e.: leads to noise).

  5. Effects of such high temperatures on the special concrete topping are unknown to this evaluator (i.e.: tension stress)

  6. Effects of such high temperatures on the rubber underlayment are unknown to this evaluator (i.e.: off gassing).

  7. Affects on any other items susceptible the high operating temperatures.

Options:

  1. Abandon the radiant floors and install radiant walls (i.e.: radiant heated wainscoting)

  2. Keep the radiant floors and add second stage supplemental heat with panel radiators or baseboard or heated walls.

  3. Keep the radiant floors and add second stage supplemental heat to the ventilation air system via a duct coil

  4. In all three cases the changes are substantive and a new design and mechanical schematic would be required.

 

Forensic Study using Finite Element Analysis
 

FEA Study: Surface Temperature

Figure 1. Required floor surface temperature above tube at new design conditions.
 

FEA Study: Flux  Analysis

Figure 2. Upward and downward flux analysis.
 

FEA Study:Isotherm  Analysis

Figure 3. Isotherm analysis and required tube skin temperature.
 

FEA Study:Thermal Contour  Analysis

Figure 4. Colour contour plots showing temperature values within the system and the new average fluid temperature based on the client proposed modifications to the floor assembly.
 

Validation against ASHRAE design graph

Figure 5. Validation analysis using Figure 9. Design Graph for Sensible Heating and Cooling with Floor and Ceiling Panels, 2008 ASHRAE HVAC Systems & Equipment, Chapter 6, Panel Heating and Cooling. Shown is benchmark case for high performance home, typical and worst case scenario based on the client proposed modifications to the floor assembly.
 

Boiler efficiency study

Figure 6. Estimation of boiler efficiency based on the client proposed modifications to the floor assembly. Notice how the efficiency drops from its original benchmark potential of 97% efficiency to just above 85% or a destruction of appx 12%  efficiency - not exactly a trivial amount.
 

Commentary:

The results of the study demonstrate the destruction of the potential high boiler efficiency due to the client proposed sound attenuation modifications.

Though there is limited studies on sound attenuation strategies and radiant floor heating systems, there are acceptable alternative methods which could be considered prior to construction, and prior to choosing flooring materials and floor assembly methods.

To prevent the unnecessary destruction of equipment efficiency and to optimize your indoor climate dollars, we recommend clients contact us for assistance prior to or during concept develop stages.

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