How Geothermal Heating Systems Work
00:06 Hi, this is John Melvin. I’m your host for the How Great Buildings Work podcast. This is a podcast where we discuss all things buildings, from construction and build methods to architecture, engineering, and systems designs. This podcast is sponsored by JM Engineering, PLLC. JM Engineering provides innovated and integrated building systems designs including mechanical, plumbing, electrical and structural engineering as well as building commissioning services. Markets served are commercial including educational and healthcare and high-end residential projects nationwide.
00:48 Our guest today is Craig Fishbach. Craig is a Heat Pump Product Sales Manager at Daikin Applied. Daikin Applied, formerly McWane International, is a global corporation that designs, manufactures and sells heating, ventilation and air conditioning products, systems and parts and services for commercial buildings. Since 2006, McWane has been a subsidiary of and Industries Limited McWane World Headquarters are located in Minneapolis, Minnesota. Craig provides training and presentations for various heat pump projects and systems throughout the United States to engineers, sales representatives and dealers. Craig is a mechanical engineer with a degree in mechanical engineering from the University of Minnesota, home of the Golden Gophers. Craig currently lives in Denver, Colorado. Craig, welcome to the show. Thank you. You started out as a mechanical engineer. How did you end up in the geothermal field?
01:45 (CRAIG) Well, I was where I’m currently employed. It was back when it was called McWane and we were a manufacturer of water source heat pumps. Primarily it started out as the traditional commercial application on a boiler tower loop. And slowly but surely it gravitated. People got thinking and people started connecting these heat pumps to earth coupled systems, moving away from a more energy draining boiler tower system. So it gravitated from boiler tower over to a closed loop, a geothermal systems. (JOHN) And when did this first start to happen? (CRAIG) I would say in the late seventies or in the 80s somewhere. We were doing quite a bit of boiler tower work and I would say early eighties, it started to get an interest in earth coupled systems. (JOHN) So, how was your thermal first used in terms of for HVAC systems? (CRAIG) Well, I think there was definitely an element of residential, single-family homes, which we as a company did not distribute in that residential market. So for us in the commercial market, I would say one of the earlier applications were government facilities, dormitories or barracks. Then I think commercially we saw a lot of activity in the K-12 school area. So I think that’s where it started. Government and schools.
03:25 (JOHN) Interesting. It sounds like a great application for it. One of the common questions is how did geothermal systems work? What are the basics with the systems?
03:35 (CRAIG) Yeah. I think that question is kind of how do you heat with some sort of air conditioning compressor? Well, I can kind of relate it to a refrigerator. So, a refrigerator keeps the goods inside cold. But it also, on the back of the refrigerator, has to get rid of heat so that we call that the heat of rejection. So we’re just lucky enough to find the reversing valve where we can operate this water cooled air conditioner in the cooling mode in generate the cold air, and we have to reject the heat to the water loop in that cooling mode. Then the reversing valve just switches it. Instead of rejecting the heat to the water loop, now we’re going to reverse the evaporator and the condenser and we’re going to take this heat rejection basically and move it over to the indoor evaporator coil and now we can heat the air. Then at the same time, while we’re heating that air, the waterside is getting colder. So it’s kind of one of those thermal dynamic rules. Don’t remember which one, but it kind of says you can’t get something for nothing. So, we have the ability to reverse the heating and cooling direction of the unit based on space demand. And when we’re cooling, we’re rejecting heat and when we’re heating, we’re absorbing heat from the water loop.
05:02 (JOHN) Gotcha. That makes sense. So, then you can use these systems for both air and water, correct? So, you can have a forced-air system as well as a substitute for a boiler or chiller. Is that correct?
05:19 (CRAIG) Yes, that’s right. But not to be confused with an air to air heat pump. So on one side we always have air and we’re heating or cooling. And on the other side of the heat pump unit, in our case, we use water. So, not to be confused with an air to air heat pump, which is air on both sides and they’re absorbing and rejecting heat to the outside air atmosphere. So, we’re absorbing and rejecting heat to a water loop. I think that’s the key right there
05:51 (JOHN) That makes sense. But then you can also have a water to water heat pump?
05:58 (CRAIG) Yes, that is another type of heat pump that, instead of generating warm and cold air, we’re going to generate warm and cold water and use it for typical application which might be radiant floor heat. So there’s always uses in a building for mostly warm water, not so much cold water, but definitely there’s uses for all buildings where they need warm water. And a water to water heat pump connects up to your geothermal loop, just like the water to air unit. But we just generate the ability to make a warm water or cold water if we need it.
06:38 (JOHN) Sure. So you had mentioned closed loop. What type of loop systems are there? How do they end up transferring this heat to and from the ground?
06:52 (CRAIG) Yeah, I’m going to say there’s three basic loop systems. I’ll start with the simple one. It’s going to be an open loop and some of us use the term pump and dumps. So if we could simply look at a Florida type application, way back in the 80s they have a need for air conditioning. So someone took one of these water to air heat pumps and hooked it up to some groundwater and pump that water out of the ground and ran it through the heat pump unit and in the heat rejection mode. So, they maybe pulled 75-degree water out of the ground and dumped it at 10 degrees higher. So, we rejected heat out of the heat pump and now we’re at 85 degrees. And that gave us the ability to cool the air. So that would be the first loop.
07:42 We would call it a pump and dump. Those systems, the pump and dump, you have to be cautious. They are dangerous. So, someone thought on a bigger system instead of just dumping water, which seems to be a waste, let’s make it a closed loop system. So, I think we could look at the people at Oklahoma State in Stillwater, Oklahoma. They did a lot of research and they figured out how to put plastic pipe, how to couple that to the earth, either horizontal or vertical configurations and how to get the right amount of heat rejection out of that plastic piping, polyethylene it was, and build it into a loop and not have that environmental danger of dumping the water to the ground or back into the ground or into a pond.
08:38 So this closed loop, was environmentally safer. It worked. It was also, I think an energy saver. We could also loop the entire building and take advantage of some units in the heating mode in some of the cooling mode. So, there was a lot of good heat transfer calculations done by the Oklahoma people. And then the third loop, we’re going to call it a hybrid loop and that basically says, I’m going to have a closed loop geothermal system, but I’m cooling dominance. So, I’d rather put in a little bit less loop and supplement my heat rejection with a closed circuit of APP cooler or a cooling tower. So that might be a Los Vegas type of applications. There’s a lot of cooling, I just don’t want to put in that much plastic pipe in the ground. So, I’m going to supplement it with a cooling tower.
09:31 So we’re going to call that a hybrid system. I’m going to say those are three of the common loop systems today. (JOHN) Interesting. Does one mode, heating or cooling generally require more tubing in the ground than the other? (CRAIG) Yes it does. I’m going to say most applications, most buildings are going to be cooling dominant. The amount of plastic pipe is, in most cases, a larger demand for the cooling mode. I guess it would be different if I were going to put a system up in northern Canada or something like that. But pretty much for the lower 48, it’s cooling demand. So, the loops are larger for the cooling mode. (JOHN) So, with the closed loop system, you had mentioned a vertical or horizontal, can you describe vertical systems, what they consist of and horizontal?
10:28 (CRAIG) Sure. A vertical system, I’m going to say the bigger the commercial job, the higher the probability for a vertical system because it just takes less land area. So, someone is going to calculate how much polyethylene pipe is needed. So I’m just going to make some simple numbers. If we need 40,000 feet of bore hole, we’re going to come up with maybe 400 feet a hole in the ground, 400 feet deep, and we’re going to do a hundred of them. So that’s 40,000 feet of boreholes. So, each one of those 400 feet of bore hole, we’re going to put up polyethylene pipe; typically, three quarters or one inch in diameter. It’s going to go down the hole and that’s going to have a U bend at the bottom. It’s going to come back up. So, this 400 foot bore hole is going to have 800 feet of plastic polyethylene pipe.
11:27 And for all of these 100 holes that we drill, we’re going to then have two pipes coming out of each hole. And then we’re going to, we use the term header them, header to them together and then bring it all together into one supply, one return pipe going into the building to connect up all the heat pump units. So, the vertical system is a series of six-inch diameter boreholes, polyethylene pipe all the way down and back. And then each one of the boreholes after the pipe is inserted, it is grouted. So, we have a conductivity from the water inside the pipe through the plastic pipe. And then, through the grout, which then closes that conductive path to the earth. So that would be the closed loop. The horizontal configuration, we would look at maybe a trench, and I’m going to say the trench might be three feet wide and a hundred feet long.
12:37 And those trenches could have the polyethylene pipe just laid into the trench in a horizontal configuration and they may go back and forth. It might be two passes or four passes within each trench and the earth that was removed would just be put back in and closed up. We have a conductivity path between the water, the plastic pipe and the earth. You just have to do a number of those horizontal trenches. Instead of trenching it, they can also just bulldoze one large pit and lay down the plastic piping and then just bulldoze the earth back over the top of it. In general, the horizontal loop is going to take more land area. So, a lot of commercial buildings don’t have the luxury of a lot of land area, so they definitely revert to the vertical borehole configuration, which takes less land area. XX
13:37 (JOHN) Is it common at all for a vertical bore hole to actually be within the building footprint? (CRAIG) Yeah, it can. Typically, I would say 95% of those are going to be outside the perimeter of the building. You definitely can use the space under the building. However, a lot of geothermal people would look at it and would question what happens if one of the boreholes generate a leak? How do we get in there? How do we valve it off? Or how do we fix it? You just don’t get access to the boreholes if they’re underneath the building. So, I would still say most of it is done after the building foundation is created, then the looper will come in and drill the holes typically outside the perimeter of the building.
14:36 (JOHN) Sure. So then with that tubing, the polyethylene, I would imagine that has a very long lifespan. Correct? (CRAIG) It does. I would say most loop systems would come with a 50 year guarantee. That’s a pretty typical number we’ve seen in the industry. (JOHN) Then, with an open loop system, the pump and dump, that would in a lot of cases consist of a supply well and an injection well, correct? (CRAIG) They would, yeah. If they have enough funds to do that, I think it may have started a little bit more basic than that maybe in the Florida area where the pump and the dump side was just to a ditch or to a pond or it got a little bit more sophisticated, people got more environmentally conscious and then people started to do a return well, so we could put the water back into the ground.
15:31 But I don’t think it started that way. (JOHN) Okay. So, then what is the difference between a water supply well, and a vertical bore for a closed loop system? (CRAIG) Yeah, the vertical bore, that becomes a closed loop system where the entire plastic piping system is close. Nothing ever goes back into the earth, just a closed loop. We just keep using that water, pumping that water into this circuit in rejecting and absorbing heat from the earth. So, the waters never really wasted. (JOHN) Sure. And in terms of the cost and the construction, a supply well would have a casing? (CRAIG) typically it would. Yup. (JOHN) So with a closed loop, you just basically drill a hole in the ground, is that correct? (CRAIG) Yeah, obviously I think the closed loop system is going to be more, maybe even substantially more than just a supply and a return cased well system.
16:39 So, I would say the closed-loop system is going to require more material, the polyethylene pipe and more labor in drilling all those different holes. (JOHN) Great. Have you come across any government regulations where you’re not allowed to put in a geothermal system, whether it be an open loop or closed loop? (CRAIG) No, I haven’t seen any restrictions, government or likewise that would prevent anybody from actually investigating and doing a closed loop system. There may be some states that prevent one from doing a pump and dump system. You’ll require permits from the Department of Natural Resources in the state. But as far as federal things, I have not seen anything that would prevent someone from doing a closed loop geothermal system. (JOHN) How about geography? Geologic concerns. Is most boring equipment capable of drilling through rocky areas fine, and does that work as a good heat transfer?
17:47 (CRAIG) I think it kind of goes like this. It’s a little bit ironic in that it’s, I’ll kind of make up the numbers. But can I give you an idea if the material underneath your feet in the ground, let’s say it’s a rocky soil. So, I put 40,000 feet of boreholes, that’s 400 feet deep, 100 holes. If it was rock, I might be able to only require 30,000 feet of boring. In other words, rock has better heat transfer capability then gravel or dirt soil. However, the type of drilling equipment to continually go through rock is more rigorous, much slower. So it ends up to be more labor. So, geography does play a role in it.
18:49 If it was softer soil, it’s just less labor. I think the rock is little bit different drilling materials and a lot more labor to drill through rock. However, it requires less tubing, but I still think the labor outweighs the material costs. (JOHN) Okay. So then if someone is going to build a commercial or a residential building on a site, how is it determined how much tubing goes into the ground? (CRAIG) That is the best question. The answer is whoever is going to design that system, they must run building load calculations. So, the amount of polyethylene pipe required is totally based on the heating and cooling loads of the space or of the building. What we’re truly trying to find out is not the fact that we have a hundred tons of water source heat pumps, but really, we want to know for each one of those heat pumps, how long does it have to run to satisfy both the heating and cooling loads of the space.
19:59 So the short answer is you have to run the building loads. I’d say 95% of the cases, people will take that load data, combine it with thermal conductivity data of the ground underneath, and use that as inputs into a computer program that will calculate how much a polyethylene pipe is needed to satisfy the heating and cooling loads of this space. (JOHN) So, how is the ground conductivity tested? Is there data out there for general areas or is there a test that’s done on each site? (CRAIG) There is data available, but I would say in most cases, what is done, we’re going to call it a test borehole and they’re going to run a test called an in-situ test. Basically, they’re going to drill one borehole, down 400 feet. They’re going to put up some plastic pipe with a U bend in the bottom and they’re going to connect it up to a device, which basically has a water pump in it.
21:12 So they’re going to fill this closed loop with water and a pump. And it’s also got an electric heater. It heats the water. They’re going to run this pump with water and turn on the electric heater. The electric heater has a given wattage to it. So, we know how much heat is going to be put into the water. And we just, over time, after pumping that water for 24 hours or 48 hours, we’re able to see how the water temperature changes. We know how much energy is going in and we can measure the change in the water temperature. And from there we can develop equations that say thermal conductivity, which is going to basically describe how good or bad the soil is at removing heat from the water. We get a thermal conductivity number, so it’s called an in-situ test done before we put that thermal conductivity value into the computer program.
22:18 (JOHN) Oh, okay. That makes sense. So then how much more efficient is geothermal over conventional HVAC systems? (CRAIG) Somewhere in the area of, I’d say 25%. So, if we look at other HVAC systems, it could be a chiller air handler system. It could be a packaged air-cooled rooftop system. We typically see 25% to 35% energy savings with a closed loop geothermal system. (JOHN) Okay. And what sort of payback then, is there a general rule of thumb for payback on geothermal? (CRAIG) That’s one way of doing it. Payback for a simple payback depending on the building size, etc., I would say anywhere from 5 to 10 years on a payback. However, the bigger buildings would actually do like a 20-year life cycle cost. So, 20 years would be an approximate life expectancy of a water source heat pump unit itself.
23:26 So if we just do the analysis, we know the amount of money required to install the system and we would look at how that compares to how much energy we save with the system. We can actually run it for years and see what sort of a life cycle cost that that entire system would have. We could compare that with the competitive chiller boiler systems or packaged rooftop systems. So, it’s more commonly done on the larger buildings with a life cycle cost analysis. (JOHN) Okay. So ,then how about maintenance of systems? Is there any difference that people need to know about in terms of does a geothermal system require more or less maintenance? (CRAIG) Actually, yeah, that’s one of the inputs to the lifecycle costs. You know, we have the operating costs, we have the initial installed cost.
24:33 We have the maintenance costs. So, one of the big advantages of the closed loop geothermal system is that maintenance costs are probably one-fourth of what they would be for a chiller system. What that means is that on the closed loop geothermal system, we do not have a boiler. We do not have a cooling tower. Basically, what we have are a couple pumps maybe in the basement or up on the roof. And we have the water source heat pump units themselves. So, we can really make it simple and say that the maintenance is, other than the two pumps, you have two change the filters and keep the filters on each one of the heat pumps. That’s basically it. Just two pumps and the number of water source heat pump units to themselves.
25:26 It becomes a very low maintenance costs compared to a chiller system with maintenance contracts and a chiller system or air handling system with greasable fittings, ball bearings and larger filters, etc. That’s one of the big advantages of the geothermal is the lower maintenance costs. (JOHN) Yeah, that’s very interesting. What sort of tax credits are available or incentives from utility companies that you’ve seen? (CRAIG) That would be on a per utility basis. We’ll see co-op’s looking for ways to save energy and they’ll put incentives with lower electrical rates for closed loop geothermal systems. On the federal government side, we have seen in the past some tax credit benefits, but recently gone away. I know that several organizations are working very hard to get those tax incentives back.
26:36 They might come back. So, we’ll just have to see how the government responds. (JOHN) Do you see any areas where closed-loop systems are more prevalent than others? And why is that? (CRAIG) Yes, we do see areas more active on the geothermal side. If I could kind of look at the lower 48, I’m going to call it the Ohio river valley and the Mississippi river valley, just kind of defines a geographical area. And what we’re really looking for is areas where in the building, there doesn’t have to be an equal balance, but there has to be some need for cooling operation like most buildings have. The building has to have a need for heating also. If we can get a closer balance between the amount of cooling needed and the amount of heating needed, it simply makes the operating costs more competitive and it’s going to make the lifecycle costs look better.
27:47 It’s going to actually make the loops a little bit smaller. So, if I could kind of zero in central Pennsylvania, a good area somewhere around Harrisburg, we could look at a lot of K-12 schools that use geothermal. If we move our geography to Phoenix, Arizona, we don’t see a lot of geothermal there. Why? Because the demand for cooling is so much greater than the demand for heating there. There probably is zero heating demand. So, the loops required in Phoenix, Arizona would be maybe twice the size of the loop system that they would use for central Pennsylvania. We need a little bit of heating. We need a little bit of cooling load. So, that kind of puts us into that Mississippi river and Ohio river valleys in the United States.
28:45 (JOHN) That’s very interesting. So you mentioned schools. How does a geothermal system differ from a conventional system in a typical school? (CRAIG) I think there’s been a movement. If we looked at schools maybe 40 years ago, even when I grew up, if they were air-conditioned, I would say schools predominantly, were a chiller boiler application. There’d be a chiller in the basement, one or two, a backup and air handlers throughout the space. We could even look at fan coils and maybe our unit ventilators, furnishing the classrooms. The transition made maybe 30 years ago, people looked at just putting an individual watered air heat pump in each one of the classrooms, larger units for the gymnasium and cafeterias. So, actually K-12 schools have become one of the major markets for geothermal and water to air heat pump systems. For myself, our company and I would say my competitors, we all enjoy the amount of business we see from the K-12 schools.
30:00 Other applications, for heat pump systems, would be dormitories for sure. One watered air unit for each dorm, high rise for the elderly, any height, high rise apartment, condo type buildings, and definitely office buildings. The office building people, the advantage with the heat pump system is that I only need to install the heat pump if and when the building is leased out. So, if it was a leased office building, we only needed to start with the number of heat pumps for the first tenant. As the tenant signed contracts, we can add heat pumps to the water piping loop. That was a big advantage versus a chiller where you’d have to buy the entire chiller for the whole building, put it in the basement. It’s all about cash flow. So, the heat pump system is much better cash flow for the contractor.
31:02 (JOHN) Oh, that’s very interesting. That’s something that I think a lot of people don’t really think about there. Let’s go back to schools. Do you see many retrofit applications of rather than a new school construction, a remodel of a school where the conventional boiler and unit ventilator system would be removed and replaced with a geothermal system?
31:29 (CRAIG) We do see that. I would say not entirely common on a weekly basis or anything like that. But what we have seen our buildings, older schools that may have had fan coil systems, which we know fed from air-cooled or water-cooled chiller and a gas boiler. So, we see some fan coil systems that want to be retrofitted to a watered air heat pump system. I guess we could also look at the older unit ventilators systems the same way, retrofitting over to a water to air system. I think what we’re also seeing now is we’ve had so many good years of water to air heat pumps, we’re now seeing a lot of replacement of our water to air units. The units are becoming 25 or 30 years old and these water to air heat pumps need replacing.
32:33 In addition to retrofitting the entire system, we’re also seeing a good market for replacing older, worn out water to air heat pumps. (JOHN) I would imagine that the newer heat pumps are becoming much more efficient than the old ones. (CRAIG) They are becoming more efficient and those seem to gravitate toward newer construction. So, if we have a 25-year-old heat pump system where the units are becoming worn out and need replacing, let’s say it’s a three-ton heat pump, it’s up in the ceiling or it’s in a closet. That particular unit is relatively small in dimensions. So, one of the markets today is, can you as manufacturers, can you build me a unit that has approximately the same dimensions as my 25-year-old units, but maybe a little bit more efficient. If I’m going to make them extremely more efficient, the units just become too big to fit the dimensions.
33:47 There’s a good market now for an average efficiency watered air heat pump that have the physical size of the units from 25 years ago. (JOHN) Oh, okay. Okay. So, the higher efficiency units actually had a larger cabinet. (CRAIG) Yes, they do. (JOHN) Interesting. Are all of the new technologies of ECM bands being integrated with heat pumps and compressor design? (CRAIG) Yeah, absolutely. I think we and the other heat pump manufacturers, we’re all offering EEC or ECM fan motors. We have various compressor technologies. It could be multiple stage, it could be a variable speed inverter type. There’s a lot of new technology that are going into heat pumps. Additionally, the type of heat transfer surfaces all of us are trying to find heat transfer devices that are not physically large. They can fit into the cabinets but still accomplish the required amount of absorption and rejection needed for the refrigerant circuit. So, there’s a lot of technology changes going on right now. (JOHN) That’s exciting. Craig, I really appreciate you being on the podcast today. It’s been a great and insightful conversation. Where can people go to learn more about you and Daikin Applied? (CRAIG) Well, our website is probably the best place, www.daikinapplied.com. There you can see all the different types of heat pumps we manufacturer, along with all of our other type of HVAC equipment. (JOHN) That’s great. Well, thanks again, Craig. It’s been very fun and insightful. We’ll look forward to talking with you again. (CRAIG) Yeah, thanks a lot. I had a lot of fun doing it.
35:38 (JOHN) Thank you for listening to today’s podcast. If you’d like more information, see our website at www.jmengineering.net or on Facebook and Instagram at JM_Engineering. Our show notes will be posted on our website at www.HowGreatBuildingsWork.com. Thank you.