Difference between revisions of "Radiant Floor Heating and Cooling"

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===== Default Settings =====
 
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The default setting is that heating/cooling to all zones. This results in the following default settings for the pumps and valves:
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The default setting is no heating/cooling supplied to the floor zones. This results in the following default settings for the pumps and valves:
 
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*** Open - 6 (adj to last temp)
 
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Revision as of 10:28, 27 April 2011

return to HVAC 2.0 Design Center

return to Living Building Design Studio

return to Sustainable Detail Design Center

What is It?

A Radiant Floor Heating and Cooling System is used to heat and cool the Green Garage building. PEX (cross-linked polyethylene) tubing will be placed below the finished floor material, in zones sized to meet the heating and cooling demands of the zone. A current ASHRAE study showed that these radiant floors can be used for cooling if they are kept no cooler than 68F. (Lower temperatures can create moisture issues in the floor.)

A Radiant Floor Heating and Cooling System can include:

  • PEX tubing. PEX comes in various diameters, with larger diameter tubing being placed at wider spacing than smaller diameter tubing.
  • With a new concrete slab, tubing is typically poured in the concrete.
  • Tubing in a floor joist system can either be applied under the sub floor between joists or over the joists in grooves of the sub floor system. With joists, a heat emission plate is typically used as well to disperse the heat over an area of the floor.
  • Also known as: Radiant heating, Solar radiant heating, Hydronic radiant heating

Why is it Important?

A Radiant Floor Heating and Cooling System is important to a building's sustainability because it:

  • Reduces energy operating costs because it is a more efficient method for heating spaces with high ceilings.
  • Adds to the comfort of the occupants by providing a more even heat.
  • Is an excellent application for the use of solar panels, used for heating the fluid circulating in the radiant floor tubing.

When to Use It?

It is appropriate to use a Radiant Floor Heating and Cooling System when:

  • The building envelope has already been improved to reduce the heating and cooling demand. In the case of super insulated buildings, radiant flooring may not produce much value for their cost, unless the building has high ceilings. See resource below.
  • It is particularly efficient in situations where there is a high ceiling, as radiant floor heating puts the heat where the people are... heating approximately up to 7' above the floor surface.
  • You have professionals available with the experience to properly install the system.
  • Sufficient space is available for solar panel installation. Radiant floor heat is a great way to utilize free energy from the sun.

Green Garage Use of Radiant Heating and Cooling

Sustainability Goals

The sustainability goals for the Radiant Floor Heating and Cooling system are:

  • Integrate the radiant floor heating with the solar panels and mass thermal storage to maximize the use of the sun's energy.
  • Meet the Green Garage heating and cooling loads per Energy-10 modeling results.
  • Our heating and cooling energy usage would be only 10% of an equivalent commercial building (per ASHRAE data.)
  • Connect the building and the occupants to natural systems.
  • Ensure a healthy indoor environment.
  • Allow components of the system to be bypassed when they don't contribute to these goals.
  • The system should be simple to maintain, adapt and control, and should position the Green Garage for a net-Zero energy future.

Strategy and Conceptual Design

Radiant Floors

The radiant floor system will be used to heat and cool the Green Garage building. PEX (cross-linked polyethylene) tubing will be placed in the sand base of the floor, in zones sized to meet the heating and cooling demands of the zone. A current ASHRAE study showed that these radiant floors can be used for cooling if they are kept no cooler than 68F. (Lower temperatures can create moisture issues in the floor.)

  • Overall Floor Designs
    • Historic
      • Existing concrete floor
      • Vapor barrier or sealer.
      • Leveling course of slag/sand on top of the existing concrete floor.
      • Two layers of 1" XPS with seams staggered. (2" total thickness)
      • PEX tubing will be placed between the sheets in the bottom layer of foam, to serve as a heat dump to help cool the mass thermal storage in the summer. This will be done only in the center of the building where the floor temperature is nearly constant, at least 10' away from the exterior walls.
      • Reflective radiant barrier (could be foil on the XPS foam boards or roll product).
      • 1.5" wood sleepers
      • PEX_Al_PEX tubing for heating/cooling loops.
      • Solid core flush wood doors for flooring. (Click here to see doors used in this application in Oregon).
  • Annex
    • The annex portion of the Green Garage is intended for use as work shop/studio. For comfort, temperatures in a workshop area are typically kept lower than those in an office environment. This, coupled with the probable need of moving (heavy) materials on some type of lift lead to the decision to keep the existing concrete floor as the finish surface.
      • Cut out 2' of concrete floor at the outside wall. Install 2" (horizontal) rigid insulation. At exterior wall, bring insulation through concrete, to finish floor elevation. This provides a thermal break to the outside block wall.
      • Place PEX tubing in area of removed concrete, and pour into new concrete.
      • Construct new wall system at exterior perimeter.
      • Use moisture resistant drywall for bottom 4', with radiant barrier on inside.
      • Install PEX tubing horizontally on inside of lower wall, with horizontal firring. Use fiberboard or plywood on inside as wall finish.


  • Fluid temperatures in floor tubing:
    • 90F maximum in the winter...higher tempeatures may harm the floor material.
    • 68F lowest temperature for summer cooling. The coolant temperature in the radiant system should not go below 68F. This eliminates any risk of condensation and the human comfort is good (i.e. no cold feet). See ASHRAE article cited below.

Integration and Controls Design Requirements

Overview

Integrating the radiant floor heating and cooling system requires significant design effort. Some of the controls will be manual and some will be automated. The key integration and control areas are:

  • The supply-demand mixing valve for the radiant floors will control the temperature of the fluid in the radiant floor tubing (PEX).
  • Integration with heat exchanger measuring the delta T of the radiant water entering and leaving the heat exchanger.
  • There are four zones in the radiant floor system:
    • Historic - Front
    • Historic - Center
    • Historic - Back
    • Annex
  • Zones are thermostatically controlled and designed to keep the flow rates of the water within acceptable boundaries.
  • Zones can heat and cool. One, two, three or four zones can heat at one time. One, two, three or four zones can cool at one time.
    • The heat exchanger can provide heating or cooling, but not both within a season.
    • If cooling is needed in the heating season the geothermal heat pump does it directly, by-passing the heat exchanger.


Default Settings

The default setting is no heating/cooling supplied to the floor zones. This results in the following default settings for the pumps and valves:

  • Pumps
    • Off - Pumps 2,3,4,5,6,7
    • On - None
  • Valves
    • Manually Adjusted Balance Valves
      • Fixed Open Position - Valves 3, 9
      • Closed - None
    • Manual Valves
      • Open - Valves 8, 10, 11, 13 - 16, 21 - 24
      • Closed - None
    • Motorized Valves
      • Open - 6 (adj to last temp)
      • Closed - None
Heating (Winter) Modes
Geo-Solar Hybrid Heating and Cooling - Shown in Heating Mode (01/22/10)
  • Occupied - Closed
    • During heating modes, radiant floor supply water 3-way mixing valve, V-6, blends hot water from the mass thermal storage tank via the heat exchanger with the return water from the radiant floor distribution system to maintain heating hot water supply temperature T-7 setpoint (90 deg F, adj).
    • Pump P-3 operates to distribute the mixed hot water to the various thermal zones.
    • Manifolds supply water to the various spaces zoned with individual thermostats.
    • When zone space temperature stat calls for heat or cooling, the pump for that zone (P4, P5, P6, or P7) is activated until the space temperature setpoint is reached (Heating 68F, Cooling 76F, adj.) Only the pump for the zone calling for heat is activated. Example, if zone 1 - historic front is calling for heat, only the pump for that zone is activated the pumps for the other zones remain off.
  • Occupied - Open
    • During heating modes, if Occupied - Open hours are designated, radiant floor heating and cooling system is deactivated and locked out from operation.
  • Unoccupied
    • Same as Occupied - Closed hours heating mode.
  • Emergency
    • Radiant floor system allows for manual override to full flow for emergency operation during the heating season.
    • Supply water 3-way mixing valve discharge setpoint or valve itself may be overridden to increase temperature of supply water in emergency heating conditions.
    • If the pump is called to run and does not run as indicated by its status monitoring sensor (current sensor), an alarm is generated in the control system.


Cooling (Summer) Modes
Geo-Solar Hybrid Heating and Cooling - Shown in Heating Mode (01/22/10)
  • Occupied - Closed
    • During cooling modes, radiant floor supply water 3-way mixing valve blends cooling water from mass thermal storage tank via the heat exchanger with return water from radiant floor distribution system to maintain cooling water supply setpoint (68 deg F).
    • Pump controls, distribution, and space stat controls are the same as heating mode, except when cooling is called for during a time when the thermal storage tanks are in Heating Mode, in which case, the cooling is provided by the geothermal heat pump through a direct connection to the primary loop. (Please note, this capability will provide some cooling, but it is only approximately 80% of the total peak cooling demand.)
  • Occupied - Open
    • During Occupied - Open hours, radiant floor cooling system is deactivated and locked out from operation.
  • Unoccupied
    • Same as Occupied - Closed hours cooling mode.
  • Emergency
    • With minimum supply water set for 68 deg F and ventilation systems maintained low indoor humidity levels, there should not be condensation on the radiant cooling surfaces. If condensation is observed or if space temperature and humidity sensors indicate system is approaching dewpoint, supply water temperature setpoint may be raised temporarily until the humidity situation is resolved.


Shoulder (Spring - Fall) Modes
Geo-Solar Hybrid Heating and Cooling - Shown in Heating Mode (01/22/10)
  • Occupied - Closed
    • In the Spring Shoulder Mode the radiant floor system will automatically respond as it normally does in the Occupied - Closed for the Heating Mode.
    • In the Fall Shoulder Mode the radiant floor system will automatically respond as it normally does in the Occupied - Closed for the Cooling Mode.
    • Refer to details in the heating and cooling modes listed above.
  • Occupied - Open
    • During Occupied - Open hours, radiant floor heating and cooling system is deactivated and locked out from operation.
  • Unoccupied
    • Operation during Unoccupied hours is the same as during Occupied - Closed hours for the mode of operation, heating or cooling, selected by the building operator.
  • Emergency
    • Operation during Emergency conditions is the same as during Emergency mode of operation related to mode of operation, heating or cooling, selected by the building operator.


Controls - Open Design Points
  1. How does the "heat dump" in the Pex tubing under the insulation of the interior portion of the floor work? How pumped? What is the path of the fluid? Needs to be shown on diagram.
  2. May use old piping in walls for some shoulder season cooling on days when temperature changes require heating and cooling in the same day.
  3. Condensation in space is often in hidden places that cannot be seen by casual observation. Consider using space temperature and humidity readings to determine when dewpoint may be an issue rather than just observation or use contact temperature sensors?


Supporting Science / Experience

The detailed thermal calculations are shown in pages included here. We thank Laurie Catey for her great contributions to our understanding of the science behind radiant floors.

Proposed Materials / Suppliers

  • Radiantec A number of good installation manuals are available here, including a towel

warming rack!

Development Story

The Radiant Floor Heating and Cooling System - Development Story page contains many images and videos documenting the process used at the Green Garage to design, build and operate our Hybrid Ventilation System.

Related Internal Links

Resources

  • Radiant Floor guide... great guide...diagrams
  • Radiant Design Software from Viega
  • Radiant over Existing concrete Design Guides
  • Building Science Report on Concrete basements...also good for walls.
  • Over existing concrete forum reply
  • Gypcrete over existing concrete is an accepted and common practice. Any "cementious" material designed for the purpose will do. If you have a walk-out or suffer from high ground water, then one inch of closed cell polystyrene would be in order if you live above the Mason/Dickson line. Each manufacturer will tell you how deep to pour but 1.5" is typical with a 1/2" cover over the tube.
  • Here's a great article showing that it may be overkill to use radiant floors in super-insulated buildings when the energy demands are already low. Environmental Building News The author states that the exception is in super insulated buildings with high ceilings.

To Do's

  • Laurie's data for floors
  • Resources
  • Short Video
  • Upload images onto Development Story page
  • Image for top of page - comes from Kevin


Gg.jpg

Peggy edited this page :)

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