New ground source heat pump questions

[cholcombe]

So I think ac_hacker might be the best to answer some of these questions. I'm living right outside of Portland now :-).
I had a salesman come to evaluate what a gshp would cost. He kinda blew me away when he said it would be 32K for a 5Ton system. I'm looking online and a fancy two stage gshp is going for 6-8K. So where does the other 24K go? Surely it can't cost that much to dig s trench for the lines.
The salesman also said something odd. I asked him if I could plant fruit trees on top of the area the lines were installed. He said sure it wouldn't be a problem. Is this true?! They proposed trenching a 60x40ft area 5ft deep. Seems extreme to me. ac_hacker how big was your system? How much did you end up out of pocket?

[SDMCF]

That's interesting because we got a few quotes around 30K euro and so decided against a GSHP. Then one guy who was here about something else came up with a price of 13K euro. He took a very different approach to everyone else. The others took the size of the house and worked out the heating requirement from that, and sized the system accordingly. The cheaper guy looked at how much oil we had been burning to heat the place and sized the system that way. The result was cheaper for 2 reasons. First, the house must be better insulated than the calculation guys assumed; sizing based on actual rather than theoretical load meant we got the benefit of that insulation. Second, because the system was smaller than the others thought it was possible to use the largest unit available off the shelf rather than a special order. I don't know how this might relate to your situation but if you have old heating bills it could be worth calculating things that way.

The 60x40ft area seems quite small to me. How much pipework are they planning to use? We used 800 metres, which was apparently double what we needed. This was in case the smaller GSHP did not cope, so we could add a second one without digging again.

As regards planting fruit trees I would be wonder about 2 things. First, would the roots push the pipes aroundeventually causing leaks? I don't know, but I would want a second opinion. Then there is the fact that trees will take moisture out of the ground and the system works better in wet ground, so how much will this effect the efficiency of your GSHP? Depends how wet the ground is to start with I guess. Again, I would want a second opinion.

[stevehull]

First, a 5 ton system in Portland would supply a HUGE house. Or if it is a smaller house, then it must have several windows open all winter long. A 60,000 BTU/hr system is massive for your area.

Tree roots are simply not a problem - be they fruit trees or anything else. The underground plastic pipe is of small diameter, is flexible and has a very strong construction. And your area is wet enough that drying out the sol via roots is simply not an issue.

Your soil type is important and especially the soil type 5-8 feet down. In Vermont, it is solid granite, so GT heat pumps are horribly expensive to put in. If it is sandy/glacial till (I suspect so), then you have no problems.

You are EXACTLY correct that you could do this yourself. Ingrims water and air has several GT heat pumps and you can get someone to dig trenches for you. Or go with vertical loops.

Another alternative is to hire someone (AC?) to supervise the installation and help out. Or barter for services - I love to do that!. All viable options.

Do you have a prior season's fuel use (electricity, propane, fuel oil, natural gas)? If so, then you have the exact number of heating units already known. This is called performance data and can be quickly used to size a system.

Performance data is actually far better than the infamous "Manual J". Performance data takes into account all the real world issues that the spreadsheet cannot imagine. Find the coldest recent winter and look up the total number of heating units for that winter (kWrs, gallons of propane or fuel oil, cf of natural gas, etc) that the house used. Most utilities keep this on file.

Each of these fuels has a heat content per unit and your heat system has an efficiency. There are calculation spreadsheets on the internet that will quickly convert the units of fuel and efficiency to a season's worth of heat.

Remember that you need several hundred feet of horizontal pipe per ton - so plan for a lot of trenching! And don't forget the lines coming into/out of house to horizontal ground loops. The specific number will be determined by your soil type, trench depth and obviously system capacity.

Then you size your system accordingly. Not hard.

Let us know if you need any help with the above.

Steve

[cholcombe]

I agree a 5 ton system would be for a pretty large house. The house here is about 3100 sq ft. It's pretty damn big. The former owners who tripled the house size in the 70's did about 1" of spray from insulation around the entire house and the attic. I had another guy come out today and said that a 4 ton system would most likely take care of everything.

Stevehull: Yeah I think I jumped the gun on this. I'm going to go through a winter and then use my performance data to size the system. I just moved here in May so I haven't been through a winter yet and I don't have the numbers :-/ I'll have to revisit this post in a few months once the cold starts getting going and see how I'm fairing

[stevehull]

The month of January will have sufficient numbers of heating degree days to do a good estimate. What heating system do you have now?

The reason I ask, is that you need to get a reading say on January 1 and then another on Feb 1. Then you need the number of units you use for heating over that time period. If you have natural gas, then this is simple as you can just read the meter on those dates.

You can get the degree days for that period (or whole year) from your local NWS (National Weather Service) office.

Propane is harder as the gauge on the tank is not quite precise enough to get a good reading.

Electricity is easy as you can read your meter, but it is confounded by lighting, baking, cooking, washing machine/dryer etc.

I would encourage you to look at your basal electricity use in October (often November bill) as this will reflect minimal heating/cooling, other stuff and this month often reflects basal electricity use.

Again, you don't need an exact 30 day period, but you do need to be able to get the number of units of fuel on the start and stop dates. I like January and February to use as performance data as the Christmas holidays screw up data with all the comings and goings.

And yes 4 tons would likely do it, but I bet with some good insulation and minimization of infiltration, you could easily get to 2.5 tons. By FAR, the best savings are with buttoning up and tightening up.

Anyone who holds out their thumb and says "4 tons" without performance data or a very strict manual J calculation should not be hired (IMHO).

Lastly, the winter usage data should be available from the utility for the last few years. Can you get that?

Steve








Steve

[dhaslam]

When you reach a fairly large size of heat pump you should also consider having two smaller ones. They are fairly reliable but repairs can be a problem. You also would have the option of using one on its own in spring and autumn.

The collector is much less expensive if you organize it yourself. It involves getting pipe and sand onsite before hand and a digger for a day plus. Also if you cannot do it yourself you need a fairly skilled person who can bring the pipes into the house and connect up. There are always problems with plumbing connections, in Ireland pipes are BS sizes and generally appliances are metric. Also connecting large diameter plastic pipe to the smaller bore header pipes need special fittings so it pays to research every connection beforehand. You should also have lots of valves, flow meters and temperature sensors to make sure everything is working properly. It is better to buy a purge pump and leave permanently plumbed in because the pipes tend to expand a little and lose pressure for a period. Plastic pipes act as a pressure vessel for short term heating and cooling. I only have an overground collector system but I think I would use long narrow trenches if putting the pipes underground. If the ground is rocky it might be easier to have vertical collector. It would require a well boring contractor and special pipe arrangements are needed so plenty of research is required.

[AC_Hacker]

Originally Posted by cholcombe

So I think ac_hacker might be the best to answer some of these questions.

Sorry cholcombe, I'm a bit late coming to the party...

Originally Posted by cholcombe

I'm living right outside of Portland now :-).
I had a salesman come to evaluate what a gshp would cost. He kinda blew me away when he said it would be 32K for a 5Ton system.

Actually, in Portland area, $32K for a 5-Ton system is a bit on the low side. If your contract specified that the installer would eat all of the 'extra costs', it would be a competitive price.

Originally Posted by cholcombe

I'm looking online and a fancy two stage gshp is going for 6-8K. So where does the other 24K go? Surely it can't cost that much to dig s trench for the lines.

Earth work is not simple or easy, and it is where the money goes if you want to hire it out.

"Dig a trench" is a considerable understatement. The trench needs to be deep and it needs to be long.

Close to Portland, a 6 ft deep, 4 ft wide slinky trench should be at minimum, 80 feet long per Ton of heating. If your house actually needs 5-Tons of heating, then you will need 5 X 80 ft of trench (minimum). There will be additional trenching required to runs the lines into your house, also. Since a slinky trench is about 4 feet wide, you would be dealing with 4 X 6 X 80 X 5 = 9600 cubic feet of earth. Since wet earth is about 100 lb/cubic ft, (not counting the trenches to get the water lines to your house) you are talking about 960,000 pounds of earth or 480 Tons.

Digging trenches may not be a straight-forward process. There may be many problems.

Living in the Portland area myself, I'm very familiar with the great geological event called, "The Missoula Flood." In truth, it was not a flood, but rather a series of floods that took placed somewhere between 15,000 and 10,000 years ago. The series of floods carried debris, clay, sand, gravel, stones the size of your fist, stones the size of basket ball, stones the sized of cars, and scattered them in each tumult of the flood in successive layers around the Pacific North West, which includes Portland. Each part is different.

This just gives you open earth to lay HDPE.

Then there is the matter of tube sizing, and tube welding, and manifold connection (if you go with an external manifold) and testing.

Then the 480 Tons of dirt and rocks needs to be replaced. All together, you will need to move almost 2,000,000 pounds of wet, heavy dirt.

Then there is the issue of dressing the water lines into your house, and assuring that there are no water leaks, if it comes in to your basement (ideal situation).

Then there is placing your Heat Pump unit, establishing the indoor manifold and valving if you aren't going to use a buries manifold.

Connecting the power legally, setting up the control system.

Flushing all the water lines with a high-power pump to assure no water voids.

Final testing to the customer's satisfaction.

So, I guess cholcombe what I'm trying to say is that there is more to it than, "...digging a trench".

Originally Posted by cholcombe

The salesman also said something odd. I asked him if I could plant fruit trees on top of the area the lines were installed. He said sure it wouldn't be a problem. Is this true?!

From the standpoint of the ground loop, he is correct, the HDPE is incredibly tough and resilient, it can take it.

From the standpoint of the fruit trees, you need to be aware that a GSHP will remove heat from the ground, and that the temperature of the ground will decline during the winter, when your home heating is required. It will warm up during the summer because of the sun.

I don't know how much you know about fruit trees, but they get their signals about when to go into a budding/flowering/fruiting cycle from the temperature of the ground.

The smaller your loop field, the lower the temperature will fall during the winter's use... the larger the field, the less the temperature drop.

So, there will be a delay, hopefully not much.

Originally Posted by cholcombe

They proposed trenching a 60x40ft area 5ft deep. Seems extreme to me.

I agree with you completely... it is extremely small.

If you were going with slinky, your 4 ft wide by 80 ft long trenches should have about 16 ft apart from each other.

So you're talking about:

80 X (4 + 16 + 4 + 16 + 4 + 16 + 4) or 80 ft x 64 ft

These are minimum numbers, a larger loop filed is always to your advantage.

Originally Posted by cholcombe

ac_hacker how big was your system? How much did you end up out of pocket?

My badly broken arm has taken a lot of the steam out of my projects, and my system is not yet finished, but it has been tested.

My design goal was to get enough heat from the ground to keep one highly insulated room warm during the winter.

I have tested my ground loop and I'm confidant that my goal can be realized.

I did several heat loss calculations, using methods similar to Manual-J, each result was reasonable, but not identical. I also logged the electric heat required through some of the worst winter days, an came to the conclusion that all these methods converged on about 2/3-Tons, worst case.

My loop field consisted of 16 bore holes, each was 17 feet deep. It should be bigger.

Originally Posted by cholcombe

How much did you end up out of pocket?

So far I have spent less than $1000, mostly on tools, like welder, and horizontal steel cutting band saw... to make tools. Some of the tools were very valuable, some not so much.

* * *

I learned that even if you totally DIY (construct your own heat pump, etc.) and dig your own loop field, the biggest amount of work is in the earth work. The amount of work in the Heat Pump is less. If you have heavy equipment, the man-hours dedicated to the loop field will be greatly reduced.

Randen did a DIY of the whole thing, with experienced help on the earth work, and he was able to leverage his considerable skill and very powerful machining tools to craft his own heat pump, which is finally working to his great satisfaction, but he certainly had his dark days.

If you want to DIY the whole thing, we will be here to see you through, though it may take a while. A 4-Ton DIY is not trivial. There was a blog that has slid off of the Internet, of a guy who bought a packaged heat pump and did all the earth work and lake-loop (he was using a lake), and hookup. When he got through, it was working to his satisfaction, and he said that he had never undertaken a project that approached the scale of his heat pump project.

There is a reputable organization called the International Ground Source Heat Pump Association (IGSHPA). They have the very best information on the subject. They also have a certification program that I completely trust. If you want to have someone do the work for you, I would seriously advise you to make sure they are IGSHPA certified.

As for advice, there is no one who has replied to this thread whose advice I would trust with out double-checking other sources.

However, if randen weighs in, it changes things for the better.

I would advise you to certainly ask for advise, but to weigh very carefully any advice, including my own, and to see if it held up to other research. I would recommend literature that is supplied by IGSHPA. Their basic manual is a culmination of 60 years of international experience, and is the gold standard of the GSHP world.

Lastly, you're probably gonna go with an existing forced air system. You need to know that to keep that place warm you will need a greater than normal volume of air flow, because it will not be as hot as fossil fuel. So, if your duct work was normal size, the greater volume of air will be audible. If you were doing this as new construction, and used over sized ducts, there would be no air noise.

* * *

In short,

• 3000 ft house is a big house
• 1" of insulation doesn't mean very much
• 5-Tons might be right, but it would indicate a poorly insulated house. In PDX, the rule of thumb is 1-Ton per 1000 sq feet. this ignores infiltration, insulation, solar gain, etc. It certainly is not an Engineered number, but it can be useful as a BS-detector.
• You absolutely need to know what you heat loss really is.
• A properly sized Heat Pump is slightly undersized, not over-sized.
• The loop field you quoted seems too small. It could result in long-term cooling of your ground source.

Best,

-AC

[cholcombe]

Wow! Thanks that was an incredible post. You raise a very good point about the fruit trees getting their annual flower cycles off of ground temperatures. I hadn't considered that. That would probably really mess them up.

From digging around in various places in my garden I've come to the unfortunate realization that there are huge rocks under the ground about 1' down. I've encountered them all over the place. It sounds like a GSHP might not be the best thing for me at the moment. I'm thinking of doing an investigation into a windmill. I want to do something ( anything ) to be part of the solution instead of part of the climate problem. I've already been disqualifed for solar panels due to heavy shading on the property from large tree's. That doesn't rule out me doing a DIY solar thing but I wouldn't get any oregon solar tax credits. Although to be honest they don't really matter when you do it yourself because of the savings. I think I need to put a lot more thought into the GSHP project. It sounds like it's likely far too large of a project for me to handle.

I'm going to wait until Feb and look at my Jan heating bill and see what that looks like. I think after that it might be worth getting a quote for an insulation upgrade. From what you guys are indicating it sounds like the house needs it.

[AC_Hacker]

Originally Posted by cholcombe

I'm going to wait until Feb and look at my Jan heating bill and see what that looks like. I think after that it might be worth getting a quote for an insulation upgrade. From what you guys are indicating it sounds like the house needs it.

Yes, retaining the heat you have is the best strategy no matter what your heat source.

Infiltration (air leakage) is almost always the number one heat loss. There have been a lot of excellent posts regarding reducing infiltration on EcoRenovator. There's plenty more great information elsewhere, too.

If you can create a mild vacuum on the house, and go around suspected leak areas with an incense stick, that can tell you a lot. Daox came up with a great plan, by turning on all of the air extractors at once (bathroom fan, kitchen fan, etc). He found that was able to produce enough vacuum to make the smoke source deflect. Cans of Great Stuff foam are very useful for sealing the leaks you find.

I also wanted to mention that some of our folks have had good luck with a Black & Decker heat leak detector.

Thermal Leak Detector | BLACK+DECKER

Reducing air leaks is the single best start.

I'm sure you will hear other good ideas here, too.

Best,

-AC