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