| This is another often misunderstood topic. Some | | | | If we are unable to deliver enough heat through |
| people insist that all geothermal heat pumps will | | | | the floor to meet the demand we could think |
| need back up heat during extreme cold. | | | | about adding forced air distribution. This forced air |
| First lets separate back up heat from | | | | distribution could have a fan coil that is getting 120 |
| supplemental heat. Back up heat refers to a | | | | degree water from the GSHP and this combined |
| way of heating if the GSHP is down and out. It | | | | with the radiant might satisfy the demand. The |
| means that there is a second conventional source | | | | other solution would have been to raise the temp |
| of heat that is there to take over if the GSHP is | | | | of the heat transfer fluid over 120 F with a |
| totally out of commission for whatever reason. | | | | conventional energy source but this has it's own |
| Now that may seem ridiculous but I can assure | | | | problems and limitations. |
| you there are a lot of custom homes in the | | | | We are limited to making the floor surface temp |
| rocky mountain west that have both GSHP | | | | no hotter than 85 degrees. Hotter than that can |
| systems and a boiler that is sized to handle the | | | | cause problems with the floor coverings and is |
| full load. | | | | uncomfortable to the occupants of the space. |
| Supplemental heat refers to a secondary heat | | | | Because of this limitation the "problem" is not |
| source that can assist the operation of a GSHP | | | | that the heat pump can only produce 120 F it's |
| during peak loads. It could be an electric plenum | | | | that even if it could be hotter we would not want |
| heater on a water to air heat pump or it could be | | | | to send hotter than that to the floor. In these |
| a small boiler or even a water heater tied into a | | | | situations a boiler would not help the situation. |
| radiant distribution system. | | | | The solution is adding distribution capabilities. |
| The real answer as to if GSHP's need back up | | | | In summary, a GSHP can be designed to deliver |
| heat has less to do with the GSHP and much | | | | more than enough BTU's to match the peak load |
| more to do with the heat loss of the structure | | | | of the project. The challenge is in delivery of |
| room by room and the type(s) of distribution. | | | | that heat energy to where it is needed and for |
| Rooms that have garage door sized windows | | | | that there are basically two options. One is to |
| and 20 foot ceilings have very high heat loss. | | | | add more distribution capability that is compatible |
| We need to meet this heat loss by delivering | | | | with low temp 120 F max. The second way is to |
| BTU's at a rate as fast as they leave the room | | | | increase the temperature of the delivery keeping |
| If the room has radiant floors we will need to | | | | in mind the other limitations that exist with regard |
| determine how many BTU's we can deliver | | | | to max temp of floor surfaces. |
| through the floor. This delivery will depend on | | | | For more information on this and other |
| type of radiant floor (slab, thin slab, staple up, | | | | geothermal topics, please visit |
| Warmboard etc), floor coverings, and | | | | GeothermalHelp.com, your online resource for |
| temperature of heat transfer fluid (120 F max | | | | everything having to do with geothermal heating. |
| with GSHP) | | | | |