Replace Furance with geothermal
craiginva
| Posted in Energy, Heating & Insulation on
Hi all!
I am new to this forum.
I have an older house with a rockwall cellar/basement..
The furnace is 19 years old. It is propane and getting close to end of life. The AC shares the same duct work.
2 questions but all input is welcome.
1. Can a geolthermal unit be installed using the same ductwork. I heard/read that it needs larger duct work.
2. Would a geothermal unit require more breakers than a traditional furnance unit? My electrical panel is full and will need expanding if needed!
Thanks,
Craig
Replies
Hi Craig,
I am new also to this forum. Last spring I installed a 5ton geothermal (running off well) in my house. Very happy with it so far!
1. Regarding your ductwork my manufacturer recommends one floor grill per 100 sqft, each with 6" supply. however, I have seen 5" used. ECM blower can be adjusted to compensate for less than ideal ducting.
2. Regarding breakers, yes you will need more room, especially if installing emergency electric backup. I think I put my geothermal pump on double 40a breakers, with double 100a for the optional electric backup.
Here is an exerp from the installation manual:
"Ductwork layout for a NORDIC® heat pump will differ from traditional hot air furnace design in the number of leads and size of main trunks required. Air temperature leaving the heat pump is normally 95º -105ºF (35-40ºC), much cooler than that of a conventional warm air furnace. To compensate for this, larger volumes of lower temperature air must be moved and consequently duct sizing must be able to accommodate the greater air flow without creating a high static pressure or high velocity at the floor diffusers."
Nathan
Thanks!
The exisitng ducting is probbly adequate
I am assuming that you are talking about a geothermal heat pump.
The ducting that worked for the propane forced air should work, if it is adequate for the heating load now.
If the propane unit was running nearly continuously to keep up you might need to increase the ducting.
The current AC unit is probably a heat pump, unless you have one of the really rare propane/ammonia units.
The existing heat pump used for cooling is adequate. So, you should be replacing a propane burner and a heat pump set up for cooling by an air to air exchange system, with an air to fluid system, that will either have a set of closed coils buried in the ground, or some water source, that exchanges the heat into the house to heat, and out of the house to cool. The new system will be considerably more efficient, so I would be surprised if it doesn't work with the existing ducting.
any heat pump solution needs to push more, lower temp air for heating than a furnace does. However, most furnaces are oversized, so your current ductwork may be adequate. "it depends". before doing anything this big dollar you should have a room by room load calculation done and an analysis of your existing ductwork.
definitely electrical equipment will need more power than your furnace, though perhaps not more than your AC, depending. We use a Daikin Altherma air to water unit that takes a 20 and a 30 amp breaker.
Disclaimer: we sell the Altherma. But that said, we chose that unit because we like air source better than geo. more predictable and less chance for major mishaps in the "source" design since it's just air.
Answers and speculation
You mention a gas furnace and AC. Assuming that your existing ductwork was sized to handle the air conditioning air flow (does the house cool well on 95 degree days?) then no need to upgrade duct sizes for a HP. Cooling will dominate your load and will drive the size of the unit, as it does in 95% of the lower 48. For a heating only system, a change from GFA to HP would most likely challenge the capacity of the existing ductwork.
Also, with a 20 year old AC unit, if sized properly, you should have all the necessary electrical capacity to replace the units. Again, this assumes that the existing equipment was installed correctly and that would include a dedicated circuit for the furnace/fan portion (1p, 20A) and a dedicated circuit for the condensing unit (2p, 30 or 50A depending on the capacity).
Making assumptions based on the professionalism of a residential HVAC contractor/installer is not a high success rate activity.
The only "wildcard" in the equation is the ground source. What is commony called a "geothermal unit" is more specifically called a watersource or groundsouce heat pump. This unit will have the fan, controls, compressor and heat exchanger in a single unit that would take the place of your furnace. All you need to do is provide a souce of water/glycol as the heat sink/source fluid. Closed-loop systems will involve a pump and like any closed hydronic system; air separator, expansion tank , auto-fill pcv, prv, etc. The pump should be a fractional horsepower circulator but still require a dedicated power circuit. If you are going to use an open system , there may be no extra pump required.
The power that feeds the existing AC should be good to feed the new unit, and the furnace power from before should be adequate to feed the circ pump. The existing ductwork will have no more limitations than exist now.
How can you say that "Cooling
How can you say that "Cooling will dominate your load and will drive the size of the unit, as it does in 95% of the lower 48.", when Craig never (that I can see) told us where he lives?
craiginva
craig in va
Ohhhhhh,"va" is a state!
I
Ohhhhhh,"va" is a state!
I thought.... he.... nevermind.
As the more observant
already noted, the name gave it away.
That and the experience of having designed/selected many gshp systems in IL and WI.
One prime consideration is usually how large the house is. There is a breakpoint (some say under 2000ft ) that it just costs too much to go GSHP over Air to Air to recover the additional cost in a reasonable period of time.
People who buy scooters new would likely learn the same thing. Despite how radically more efficient a scooter is over their vehicle, they will never recover the cost due to the limited miles they will put on the scooter.