Ground Source Heat Pump - Calculators and Good Idea (?)

A lot of this comes down to personal use, proper maintenance and quality of installation, plus incentives you are able to acquire...sizing the system and installation is best left to a reputable dealer.....payback time is relative to current costs, and is a ballpark figure anyway...By adding what your current expenditure for heating and cooling is now, and the improvement in efficiency of the system you are installing, will yield the approximate savings in operational costs...What you expect to save a year in heating and cooling costs divided into the net installation cost, will give the number of years it will take to actually start saving money...

http://www.gshp.org.uk/

Thanks, SolarEagle, I do appreciate what you've shared so I may determine what savings, if any, I might generate. I'd like to be able to develop something better than a ballpark figure (meaning, an estimate, for those unfamiliar with a sports term) on my own and THEN have the dealers prepare quotes. I don't mean to disparage any dealer or business owner but I just don't have enough experience in the market to know who is and isn't a reputable dealer. I'm not smart enough (yet!) to know what questions to ask and I'd like to have a level of knowledge on my own where I can build a rapport and a certain degree of trust with the dealer community. Does that make sense?

No not really, any reputable dealer/salesman will have all the facts and figures, trying to second guess an expert will just make you look overly anal, and insult the representative by making it look like you don't trust them....This then labels you as a problem customer and leads to a resentful attitude on the part of anybody dealing with you....Your role as a customer is to expect expert opinions, and take them as gospel....this gives you a superior bargaining position should something go wrong....

I refer you to the Godfather quote, "I will not be the one to break the peace"..

#1 problem behind ground source heat pumps systems is the average ground temperature.

If you're under 60 F your screwed on heating efficiency with one. You Will have super cheap air conditioning capacity but for winter heating there isn't enough workable thermal energy to be viable for very long.

It's a common problem where I live being our average annual ground temperature is in the mid 40's to low 50's at best which I think Massachusetts is similar worse.

US soil temperature map.

Why would the 2-5 cm layer be relevant for ground-source heating/cooling calculations? These temps sound like seasonal numbers that will change in the next few weeks, anyway. As a minor glitch, the legend omitted one of the colors that showed on the map.

..."Many people often ask how deep the wells need to be dug for geothermal systems. The answer to this question is always, “It depends.” The reason it depends is because there are many different factors involved in the sizing of the geothermal loops, and many different designs as well. I have been to geothermal installations where the loops ranged from only six feet underground, to the 1,600 foot geothermal wells at the Peace Center in Philadelphia.

The real factor involved in how the geothermal wells are placed and the design that is chosen is driven by cost, the amount of space available, and the size needed to heat and cool a building. When there is a large amount of space available and cost is a consideration, horizontal geothermal loops may be chosen that range from six to twenty feet underground. Other than placing coils of loops in a body of water, this can be the most cost effective way to place geothermal loops. In the example of the Peace Center in Philadelphia, a large skyscraper needed to be supported by geothermal wells in a very limited space. This is where the 1,600 foot wells come in with a unique design known as standing water column.

With considerations regarding cost, the amount of space available, and the size of the system that is needed to heat and cool a building, a geothermal contractor or engineer will custom design a geothermal loop field. It is important to note that you should check to ensure that your geothermal contractor has been through a formal geothermal design or loop certification program such as IGSHPA (International Ground Source Heat Pump Association) or a certification offered through a geothermal manufacturer. For more information about the different geothermal loop designs available, feel free to refer to the Outdoor Portion section under Geothermal 101 on this site."...

http://www.geothermalgenius.org/blog/how-deep-are-geothermal-loops

Huh? What does that have to do with 2-5 cm deep?

More like 2-5+ meters deep....

That may be reasonable, but it isn't what the map legend said.

Run out of OCD meds this week?

Ahh, SolarEagle, I didn't realize this post was also yours and you've provided an important insight here and resources that I very much appreciate. I know there are different ways to 'put the pipes in the ground' and now I can determine what may be best and what may be cost-effective (which are not necessarily the same thing).

It does beg the question (since I've worked in the plastics industry) as to what kind of lifetime the plastic pipes may have before they deteriorate? And, what kind of maintenance, repair or overhaul (replacement) are possible (and at what cost)?

"...It does beg the question..."

No it actually doesn't. It might 'raise the question', 'prompt one to ask' or even 'suggest an inquiry', but 'begging the question' has a distinct important meaning.

'Begging the question' refers to a logical falacy wherein a proposed argument is merely an unsupported restatement of the premise, e.g."Of course he is the best choice, no one else is better."

There are many other ways to something brings you to another question, so use one of the alternatives and save 'begs the question' to its unique and useful meaning.

Okay. For deeper soil temperatures.

US groundwater temperature

Looks to be the same range of numbers as the other map and pretty close to what I have here being my well is 200 feet and my groundwater is in the mid 40's F range.

I think it will help to clarify two distinctly different methods of circulating water underground. I've seen two and I think there's some confusion in the discussion.

What's pictured above is the method where the loop is placed in a trench and covered with soil. The trench will need to be significantly below the frost line to avoid seasonal effects on heat transfer. This makes it less viable in northern latitudes.

A more common method in my locale, northern end of Delaware, is to drill two wells and pump water out of one and back into the other. Catching the right aquifer can yield fairly stable temperatures, in this location typically in the mid 50 deg F range.

Yes called the 'Standing Column' well....most geothermal wells in Mass. are this type...

Thanks, NEL. I've heard that some people will draw from and discharge to an open waterway (lake or river). In such a case I should think that fouling might be an issue and that filtration and other measures may be required.

And, in the approach you've shared (as well as with the open waterway option), are there any environmental considerations with regard to the discharge? I don't mean to put it on the same level as what the 'fracking' world has to address but, just the same, the environmentalists might take issue with the approach. I hope I'm way off base. Am I?

I've often wondered about that. I don't have any direct info, but my guess would be that very little surface impurities/contamination will join the returning water. Most likely whatever may leach from the metals in the pump and pipe fittings or from the plastics as well. That's in the parts-per-million or smaller concentrations unless the water is really active. There's really not much of an opportunity for anything else to get into the system.

I ran into an issue a few years ago. After a period of time the geothermal heat pump lost effectiveness. The cause turned out to be loss of soil moisture due to heat dissipation into the soil during the air conditioning cycle. As a result, the soil lost heat capacity and became more insulating due to drying of the soil.

If using the system, you need to pay attention to soil percolation and water recharge capability to maintain effectiveness of the system.

Thank you, Jpfalt. These are the kind of issues that might not be very common or might be very easily addressed at the outset, BUT they are the stories that spread like wildfire and create all sorts of consternation, reservations and, ultimately, impede the market from adopting new approaches. I mentioned in an earlier post that I'm concerned that my knowledge isn't sufficient to even know what the right questions are. And, here, you've highlighted just one of those issues that I (and maybe even industry veterans?) might not appreciate until well after the system is installed and not meeting expectations for performance and savings.

Seasonal usage is something that is a huge consideration that I have yet to see many of the professional installers ever discuss in most parts. There's only so much thermal energy the ground can sink or source before the efficiency of the system drops of to being near useless.

Its very much the same as usings battery. There is limit to how much energy you can take out and how much you can put back in given the realistic heat pump system limits.

In my area summer air conditioning operation does not put enough thermal energy back into the ground to offset the winter heating drains given our rather low average ground temperatures so that makes geothermal heating pretty limited and thusly have a very long payback period.

Something that in the south they have just the opposite effect in play for . Their ground temperature is naturally high enough that they start to get diminishing returns on summer air conditioning capacity but in trade they have excessive winter heating capacity.

The battery analogy only semi-applies. If below the water table, then conduction past the loop-bed and normal groundwater circulation can act as sources or sinks and you can't bank the BTUs you put into or pull out of the ground. If above the water table, the thermal cycling of the soil leads to the depletion of moisture which does act to reduce it as a BTU bank. You need to maintain your thermal soil bank by watering it regularly and maintain the health of the system not too differently than you would maintain a septic tank and drain field.

Personally, I like the pumped water system if you have a ready source of free shallow surface groundwater and a place to put it when you are done with it, although you can easily lose the system in a really dry year. You also have the potential to introduce groundwater contamination depending on your local circumstances.

Around here thermal depletion is the biggest problem. Ground water movement at the depths most systems get installed at just doesn't provide enough seasonal recovery for the typical what loads our winters require.

Around here once you freeze your ground loop solid nothing in terms of ground water gets displaced until it thaws and with a mid 40's seasonal ground temperatures if you freeze the ground solid below the typical 4 - 5 foot frost line depth it tends to just stay that way for the whole summer season. Hence the need to put heat back in to make the system work.

Our local college put in a huge geothermal systems a few years ago while I worked for a local business whose rental equipment was on the site.

I got to talk with the suposed experts about the system when ever I made service calls to work on our rental machines and they claimed that it was going to supply 100% of the colleges typical winter heating and they would be tearing down the old coal and natural gas fired central boiler plant afterward to make room for more parking lot.

Well, a few weeks ago I was on campus for the Science Olympiads working with one of the local schools and asked the one professor I know that does environmental research and related class work about how the the geothermal system worked out, being I know he took a strong interest in the project and would give me the honest inside story.

"Not worth a shyte." is what his answer was to how well their super system turned out. The old boiler plant is still standing and still very much in use for the vast majority of the winter because apparently not one of the experts took into account that the heat load a college campus takes is about 10 - 15x what the natural ground recovery rate is in our area.

It suffered the same problem pretty much every geothermal system in our region runs into which is once you freeze the ground loop soil mass it stay that way for a very long time unless you put heat (a lot of heat) back into it.

I know of at least a dozen homes and businesses who put them in over the years I can say pretty much everyone of them came out way short on what they are supposed to deliver for what they spent and far from what the experts who sold them the systems told them.

Sure they will keep you from freezing to death in the winter but for a system that takes 20 - 30 years to break even and only gives you 55 - 60F tops inside temps in the dead of winter without supplemental heating assistance it's nothing to brag about.

Around here they are cheaper per heating MBTU than electric but no where close to matching utility service natural gas or propane or as the college, dirt cheap coal.

Now however for air conditioning they are crazy efficient since the condenser side of the system if typically running in a block of ice for most of the summer after the first winter run!

tcmtech, I may be a bit more dense than I care to admit: Are you saying that the fluid in the HDPE pipes actually freezes in winter so the system is not functioning?

No. The systems I am familiar with run with either ethylene glycol or propylene glycol antifreeze in the lines.

The problem is the ground itself is what freezes up so depending on what your natural ground temperatures are at the depths of the lines that frozen ground may take a long time to thaw out enough for water to start moving through it again and bring its temperature up as others have mentioned.

Around here with natural ~45F soil temperatures ground source heat pump systems are well known for having poor performance, especially after a hard winter, and some never work properly after their first year due to inadequate thermal recovery of the soil.

Theres a reason the soil is naturally that cold at that depth and beyond to begin with. Nature just doesn't put much heat back in the summer time in normal conditions so if you're intentionally sucking far more heat out of the same soil mass it will take longer to warm back up on its own and if enough heat is taken out it can't recover properly before the next winter comes.

Interesting input on performance. Thank you for the insight. I've read (somewhere) that Canada has a larger number of geothermal installations. I have to wonder about their experience with low natural ground temperature. Of course, there are likely areas that are not subjected to these environmental extremes but I should think there are locales (north of Minot, ND, for example) that might not be suitable.

The poorly definable location specific will or won't work issues is what I see as being the largest stumbling block behind these systems.

As others pointed out if a system was setup in one location that has good ground water movement characteristics that reheat the ground loop it would likely work well there even with low average soil temperatures.

Yet if set up in another soil that has very poor ground water movement it won't work nearly as effectively or after item not work at all unless it has a considerable amount of artificial ground heat replenishment being done to it outside the heating season.

I can see where on my own property that simple soil type and ground water movement issue would play a huge roll in such a system. Where I am at in less than 100 feet my subsoils go from solid near impervious high clay content glacial loams to high permeability sand with a naturally high groundwater level and rate of movement.

To be honest I have suspicions that is where the local college hit its snag with it's system. The location of their main thermal wells is basically the same types of soil much of my yard is which is the low to near non permeable clay and heavy loam based stuff.

As the college officially brags about its system..

Minot State University Geothermal heating system. PAges 4 - 7.

In 2011- 2012 ~$16.5 million was spent to avoid a ~$10 million dollar heating plant overhaul with the intent to be a 100% geothermal heated campus running off some 1000 wells by 2014.

Unofficially however.

It's 2017 and um, well... they are in fact no where near 100% geothermal. (and really don't want to talk about it publically either) rather, the heat plant didn't get torn down to make room for more parking lot space but instead got a major overhaul being the geothermal system apparently fell on it's face in performance and capability when we got back to our normal ranges of cold winters in 2015/16 and 2016/17.

Sure, it worked great until things actually got cold here.

Friends,

I have been out of the construction field for over 12 years, but I knew (KC area) of one contractor building and installing his own GSHP's more than 30 years ago! That was when I was very active in our local Solar & Energy Association, which sponsored the early Energy Expo's in our area The technology has come a long way since then. At that time the rule of thumb was 100 feet of ground loop or well per ton, but I suspect it is more refined today.

Ground temperatures, as others have pointed out, vary significantly over the seasons. If you plot or graph average temperature by depth and by day-of -year, you will see that there is a lag between extreme air and extreme ground temperatures that gets later and later as you go deeper. At the same time the annual swing in temperatures gets smaller and smaller. In many cases when you get around 30-ft (10m), the lag is close to 6-months (higher ground temperature in winter!), and the swing is well under 1-degree.

--JMM