HVAC GeoThermal Heating and Cooling

[davew26]

I have been using a geothermal heating/cooling system for thirty years and love it. I circulate water in 2,000 feet of 2" polybutyl pipe in a closed loop system. We decided to add on to our house and have added a second geothermal unit. It is installed in series in the closed loop system.

A problem I now have is when both units are running at the same time. The first unit will take the water temp down from 70f to 40f and then the second unit takes the water temp dangerously close to freezing. I have had to only run one unit at a time by manually turning the heat/cool/off switch to off on one of the units. The weather has been mild so far but it may be a problem when the weather begins to freeze.

I have a Arduino board i can use to control the cycle and i can detect when either unit is running. But to control the units I am using Crydom 5A 240v solid state relays. The relays operate with 3-30vdc. The ARduino board can easily control the relay. The unit transformers are 24vac and i can either break the 24vac or the 240 vac side to shut off one unit when the other one is running.

I like using the Arduino because it can read and record in my old computer the outside temp, unit 'Air In' and
'Air Out' zone temps and in and out water temps. Then i can check the performace of both units.

Which should I control? I thought about installing two Crydom relays in each unit breaking both sides of the 240 vac feed to the transformers. If i use one relay on each unit to control the 24vac control (red wire on most ac thermostats) is there a chance i will blow the transformer which will still be powered by 240vac?

Any thoughts would be appreciated.

Thanks Dave

[MrAl]

Hi there,


It depends on how long the transformer has to run for. If it has to run for short periods of time, then turn off the 240vac side, but if it runs for long periods then turn off the 24vac side. It's better not to have the transformer running for long time periods unless it has to run that way anyway.

[davew26]

Thanks for the reply.

I timed the unit running periods and it is usually 3 to 10 minutes.

I am afraid of leaving the secondary open. I remember how easily the audio output
transformers would blow if you power up an amplifier with no speakers attached. This
was on older amps but Would probably still apply to a power transformer.

The control transformer is powered by two 120vac lines. I will have to use two solid
state relays to kill all power to the transformer. But the Crydom relays seem to be
reliable.

Thanks again
Dave

[dacflyer]

what about running the system in parallel rather than series...? not possible or ?

[davew26]

what about running the system in parallel rather than series...? not possible or ?

I tried running them in parallel, didn't work well. The pipe is 7 ft underground and runs back and forth in a side yard. Luckly we have a long 3 acre lot so there was plenty of room. The engineers calculated everything for one-inch pipe but prices were good in 1980 so I bought two inch pipe for extra capacity. Inside the house I split the line into two one-inch lines and adjusted valves and pumps to feed both units. Water like electric current follows the path of least resistance and could never get the flow even. Series is better. But only one unit at a time. The air ducts and returns connect so actually when either unit runs it serves the entire house but the rooms closer to the unit get greater flow. There are separate thermostats for each unit.

I will try the two solid state relays this week. Will post the results.

Dave

[ltx71cm]

Just approaching from a different angle here, can't you use antifreeze? (GTF antifreeze)

I have no experience with geothermal systems so I may be missing something but from my viewpoint if they make the product, it's got a use. If there's a reason to not use it please inform me so I know why going forward.

[davew26]

Yes, I could use antifreeze and I do use some I dilute my water with about 5% Propylene Glycol. That lowers the freezing temperature some. My closed loop system contains about 350 gallons of water and Glycol. The heat exchanger is capable of dropping the water temp down to around ten degrees but heats best when the water/glycol temp is 40 f or better. In the summer it heats the water up to 110 f.

There are a few pin hole leaks in the closed loop system and I use a boiler fill pressure valve to keep the loop filled and under constant pressure of 15psi. Getting air in the line is a headache. I finally installed freeze proof water faucets on the high side (up a hill) of the closed loop and about once every three months go out and bleed the system.

I have to check the ph value of the water to keep my slightly acidic water from damaging the metal heat exchanger. I just pump in some baking soda.

With all the extra jobs it gives me it is still easier to maintain than oil heat as my neighbors use. They have servicemen out two or three times a year. Geothermal is a lot cheaper than oil or electric heat.

I got the idea from a Popular Mechanics article back in 1979. Trane, ComfortAire, and most other Heat Pump manufactures build geothermal heat pumps and the IRS gives a nice tax credit for buying one.

Dave

[Bob Scott]

I am afraid of leaving the secondary open. I remember how easily the audio output transformers would blow if you power up an amplifier with no speakers attached. This
was on older amps but Would probably still apply to a power transformer.

No Dave. Very old transistorized audio amps using output transformers may have had this problem blowing output transistors due to inferior early designs and old model failure prone germanium transistors, but you won't harm the 24V transformer by leaving the secondary open.

In 35 years of repairing home/industrial/broadcast electronics I have never seen an amp blown this way, which makes me suspect that the caution may be just urban legend.

The control transformer is powered by two 120vac lines. I will have to use two solid
state relays to kill all power to the transformer. But the Crydom relays seem to be
reliable.

Crydom and the other brands of solid state relays use triacs. They may not be as reliable as you assume. Our lighting control board at a TV studio used SSR's. They needed replacement quite often as the triacs failed "OPEN circuit". However I think they are good enough to use, if you keep a replacement on hand in case one fails in an HVAC system. They are easy enough to change.

Also, check the manufacturer's specifications of the 24 volt transformer to see if it has sufficient current capability to drive that extra relay. If not, just use a larger model.

[harlywalter]

HVAC GeoThermal Heating and Cooling combined with a VRF (Variable Refrigerant Flow) system is an excellent choice for residential applications. Geothermal heating and cooling leverage the consistent temperature of the earth to provide efficient year-round comfort. This system utilizes a ground-source heat pump that extracts heat from the earth during the winter and dissipates heat into the ground during the summer.

When combined with a VRF HVAC system, the benefits are further enhanced. VRF systems employ advanced refrigerant flow control technology, allowing for individualized temperature control in different areas of the home. The VRF system utilizes a single outdoor unit connected to multiple indoor units, which can be adjusted independently for personalized comfort.

The combination of HVAC GeoThermal heating and cooling with a VRF system offers significant advantages. Geothermal energy provides consistent and sustainable heating and cooling, while the VRF system maximizes energy efficiency and comfort. Additionally, the VRF system's zoning capabilities enable precise temperature control, reducing energy waste and ensuring personalized comfort in various rooms or zones of the house.

In summary, integrating HVAC GeoThermal heating and cooling with a VRF system in a residential setting delivers efficient, sustainable, and customizable comfort throughout the year.