cast iron radiators with geothermal?

imatellerslie

Based on some calculations I've made for heat loss, a 5 ton geothermal system will heat my house until ambient temp drops below 39 degrees. At 10 degrees, the house loses almost 130,000 BTUH. I don't want to put in twice as much capacity in geothermal to keep the house warm for a relatively small fraction of the year. I think it would be much more economical to use a boiler to supplement the geothermal on those cold days. In fact, I bet a 5 ton geothermal system will heat the house to temperatures lower than 39 degrees, because i'm going to put in 5 or 6 zones, and TRV's on each radiator, and will probably keep a lot of the rooms colder than the 68 degrees that gave me the 39 degree failure temperature. I wrote a spreadsheet to experiment with the numbers. It's posted at the end of this thread.

Thanks for the reply!

imatellerslie

cast iron radiators with geothermal?

I have a 110 yr old house that I'll be installing all new mechanical systems in. It can be seen at http://home.earthlink.net/~rnfelts68

The house originally had a convection hot air furnace. It was retrofitted with a hand fired steam boiler and cast iron radiators in every room (19 radiators).

I would like to install a direct exchange geothermal heat pump, and am wondering if I can use the old radiators with the low temperatures provided by the geothermal system. As I understand it, a geothermal heat pump would give me about 120 or 130 degree water. I did a Manual J by room, so I have a pretty good idea how much heat the house will lose, but I don't know how to determine how much heat the radiators will provide.

Thanks in advance!

Luke Lefever

First you need to figure out the EDR for the radiators you have.

You can do this by looking through Dans book entitled,oddly enough EDR.. ratings for Every Darn Radiator. The EDR will tell you how many square feet of radiating surface you have for your style of radiator... with that information you can know how many BTUs each will emit into your living space. You compare the capacity of the radiator to the heat loss of the space and viola, you will know your answer to whether you can get by at 120 or 130 degree water. My guess is that unless the house has seen substantial thermal improvements, radiators that were adequate at 212 degree steam might not be adequate at 120-130. Then there is the question about converting steam radiators to water.. but that's a different thread. Good luck, Luke Lefever
Lefever Plumbing & Heating, Inc., Elkhart, Indiana.

Luke Lefever

If you're in MD near DC, you want Steamhead!!!

Mike T., Swampeast MO

Rad output

Check your mail--caught a glimpse of a rad in one of the photos and it is a thin-fin tube rad of the "standard" variety I believe. Many makers, but output was quite standardized.

Are you certain it is steam? Sometimes a lot of confusion. If you see "bulled shaped things" on the rads and have only one pipe it is steam. If there are two pipes to each rad look for a "sight glass" on the boiler--a little glass cylinder with water inside--if you find such it's steam.

While old systems were typically oversized by modern standards, "normal" steam is quite hot and I highly doubt the radiation would be sufficient with 120°-130° water in cold weather.

If it is a water system AND it was greatly oversized AND you have insulated/weatherized VERY well you MIGHT be able to use 130° water temp. To get a very good estimate of output use this formula:

Rad Output in btu/hr = ERD * ((Avg rad temp - air temp) * 1.5)

Average rad temp can be quite safely assumed to be 10° below the supply water temperature so...

If you have 130° water and assuming air temp of 70° EACH square foot of EDR of those radiators will give off about (120 - 70) * 1.5 = 75 btu/hr. Multiply 75 * the EDR for the radiation in each space and compare to your heat loss.

Seven fireplaces? I know they can be charming but they are notorious for heat loss at ALL times. With a fire burning in an open fireplace using heated indoor air for combustion they are actually a net heat LOSS!

Likely you will find that you'll need higher water temperature. That does NOT though mean that you can't use geothermal--you'll just need to give it a "boost" during really cold weather. A small boiler can be installed for this purpose and it will only run when outdoor conditions require it to run.

Good luck and have fun!

imatellerslie

Who is steamhead!?

Thanks for the reply Mike. I'll try to determine the EDR for my radiators and go from there. I'm about 15 or 20 minutes outside DC in Maryland. Who is steamhead?

imatellerslie

I think it's steam because...

there were pipes sloped back to the boiler in the basement. Each radiator has two pipes leading to it. One pipe wasn't sloped, and the other was. The system had a circulator when I bought the house, but I was thinking it was a retrofit. I dunno.

As for the fireplaces, I am planning to add chimney cap/dampers on top of all the functional fireplaces to minimize infiltration/exfiltration from them. Something like this: http://www.dukefire.com/locktopdampercap.htm

I'll try to determine the output of my radiators using the information you gave me. If my system was actually a water system originally, what would have been the operating temperature? 180 degrees?

I think the boiler and radiators were added to the house before it was insulated. The radiators are quite large. I have one in a bedroom upstairs that is over six feet long.

The idea of using geothermal and adding a small boiler to make up for the deficiency in cold weather appeals to me, but I'm not sure how that system would work? I presume the boiler would have to heat the supply water after it passed through the geothermal unit. Wouldn't the geothermal unit have problems if the boiler drove the return temperature too high?

I would like to use radiant floor heating in the kitchen and bathrooms. The house had a plaster ceiling in the basement, but I took it all down to gain access to inspect structure and to help dry out the basement. I now have access to the underside of all those floors, but I don't know how it will work with radiant heating.

I'll try to figure out how to use EDR and make some calculations. Thanks for your replies!

imatellerslie

a radiator and the boiler

imatellerslie

Mike T., Swampeast MO

The pipes are sloped back to boiler because:

1) If originally a gravity system it HAD to be this way for the gravity circulation to work.

2) It's ALWAYS good plumbing practice to drain EVERYTHING back to the lowest point, i.e. the boiler. Easier to drain, easier to fill and easier to remove air!

If there was a circulating pump it is a hot water system. Steam moves by means of its own motive force--it's EXTREME expansion when it changes state from a liquid to a gas. Sometimes there are condensate pumps or vacuum pumps in steam systems but I believe these are very rare in residential applications.

The table I sent you should make it very easy for you to calculate the EDR of all your rads. Add all the radiators in a single space together for comparison to your heat loss calculation. For the purpose of heat loss any rooms connected by a permantly open opening greater than 4' or including an open stairwell are considered the same space... Of course that doesn't mean you can put all of the radiation in such "connected" spaces into a single room and expect decent temperature balance

I haven't worked with a hydronic geo system but if high return temps from the boiler "boost" would be a problem it would be quite simple to employ a mixing technique to keep the temp down. However as I suspect you have a converted gravity system, generally the LEAST of your concern is keeping the return temp DOWN!!!!

As long as a highly conductive method of heat transfer is employed (heavy extruded conduction plates, Warmboard, etc) radiant and geo should be a wonderful match.

Unless you're an EXTREMELY hardcore DIYer who is willing to study a LOT, I'd suggest you find a good heating contractor. Hopefully you can find one familiar with Geo, Hydronics AND Radiant but if not the Geo guys and the Hydronic/Radiant guys should be able to work well with one another.

Again, check the output with the formula I gave with the EDR and your heat loss calculation. You're likely to find that some spaces/rooms can be easily satisifed with 130° water at outside design conditions while others are lacking. Your home looks as though it has a number of rooms with three exposures (read very high heat loss). Insulation/weatherization tends to affect these more than spaces with one or two exposures.

Please give utmost consideration to thermostatic radiator valves (TRVs)!!!!!

Steamhead

Thanks, Luke & Kevin- Here I am

From your description of the piping and the fact that it has a circulator, it's probably a hot-water system. Some more clues: If each radiator has a manually operated air vent on one end at the very top, and the return pipe is the same size as the supply pipe (applies to mains as well as radiators) and there is a tank either in the basement or the top floor or attic connected to the system for the water to expand into as it's heated, then you have a hot-water system.

In the old days, these systems circulated by gravity. This explains the big pipes, which were needed to keep resistance to a bare minimum. The usual design criteria was to heat the house to 70 degrees when it was zero outside, and the boiler water was no hotter than 180 degrees. This is why the radiators were so big- remember, this was done at a time when houses did not have insulation, storm windows or weatherstripping like they do (or should have) now.

Some gravity systems used devices like the Honeywell Heat Generator to carry a slight pressure on the system so the water wouldn't boil at higher temperatures. This method allowed the use of smaller pipes and radiators. Nowadays we do the same thing with pressurized expansion tanks.

I have an old hot-water system in my house which works very well. I've added thermostatic valves to the bedroom radiators which limit the temperature in those rooms.

Since you've already done the heat-loss, get a copy of Dan's book "E.D.R." which has radiator sizing charts. Order it on the Books and More page of this site. Compare the actual heat loss with the installed radiation. You may find that the radiators can run with a low enough water temperature to make geothermal worthwhile. But it might not be a bad idea to keep the boiler as a backup.

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kevin coppinger_4

Steamhead is an Artist....

when it comes to heating systems..especially steam, he is in the Baltimore area. You have a very old delapitated system...cast iron rads are nice way to go if you set the system up right. Geothermal can be nice but the set up is a big initial investment...good luck. kpc

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Mike T., Swampeast MO

Oh my...



...I can certainly see why you want to dry out the basement. Is there a spring/stream running down there (serious) or "just" leakage problems from the roof?

Mike T., Swampeast MO

Oh my...

...I certainly see why you want to dry out the basement! Is there a spring/stream running down there (serious) or just roof problems?

Scale is hard to tell but I believe that is a water system originally designed for forced flow. I'm quite ignorant regarding steam but I don't see any of the things I normally associate with a steam system.

Steamhead

That's hot water

the tank mounted above the boiler is the expansion tank I mentioned in my original post.

Looks like that house had been abandoned, but it has potential. The first thing to check is whether or not the radiators and piping have been frozen. If so, they will leak. But you can still get radiators, both new and used.

You will also need an asbestos contractor when you replace the boiler.

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imatellerslie

It had a circulator and expansion tank, and the supply and returns are the same size, so I guess it was always a water system. I thought maybe it was originally steam and was converted to water, and that the circulator & expansion tank had been added. I thought steam because of the fairly significant slope of the return pipes in the basement, and because the piping was black steel. The pipes were very badly rusted, and I've removed most of them from the basement. The joints on a number of them just fell apart when I pulled them down. The house has been sitting vacant for about 20 years, and the pipes were badly rusted from condensation gathering on them in the summertime as the humid air blew through the basement.

The pipes that drop from the rooms into the basement seem to be in good shape. What should be used to restore supply and return to the drops? Copper, PEX, other alternatives? If copper, how do I avoid electolysis at the transition?

imatellerslie

system drained

When I bought the house, I found a hose leading from the boiler to a drain in the floor, and several other drain valves in the system open. Also, I found the air bleeders? removed from the radiators, carefully placed in plastic baggies and attached to the window by each radiator with a tack. I'm hoping these are indications that the system was drained before it froze.

It has been empty for about 20 years.

kevin coppinger_4

My vote would to...

set up a couple of manifolds off a new boiler, or the like and home run to each rad in 1/2" pex. You could then add a TRV(thermostatic radiator valve) to each rad. Set it up off an outdoor reset control and have a VERY nice set up. I'd opt for a nice oil fired Buderus boiler. kpc

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imatellerslie

inadequate drainage

The water in the basement is due to some roof leakage, and also a lot of it is simply condensation that happened in the cold basement as the warm MD air blew through in the summertime. I have removed most of the heating system piping in the basement, since it was shot anyway.

imatellerslie

cost

I made some cost calculations based on the Manual J I did. Assuming that the house is at the conditions for max heat loss all the time (worst case scenario) it would lose 130,000 BTU/H. My calculations, based on the electicity and gas costs in my area, a 90% efficient gas boiler, a heat pump with HSPF=7.5, or a geothermal unit with a COP=3.5, show the following:

heating with gas would cost me $832/mo
heating with an air/air heat pump would cost me $604/mo
and with geothermal $134/mo

That's why i'd like to try to make geothermal work, regardless of the high initial cost.

imatellerslie

Here's a picture of a couple more radiators

Steamhead

130,000 BTUH

In that range you have many options.

You don't want a standard air/air heat pump- these were designed to be cheap to install, not for comfort. And don't forget, in cold weather like this most heat pumps switch to electric resistance backup, which is very expensive to run. I would never live in a house with one of those.

Have you considered oil? Check out the Burnham Opus boiler- I've heard many good things about it. Also, Columbia now sells a version of the Biasi boiler. Both have higher AFUE ratings than the usual oil-fired boiler.

There is some debate about whether a condensing boiler would save much when used on an old radiator system, due to its higher operating temperature when compared to radiant floors. But we don't know yet what temperature your system would need.

I think if I were designing that piping system, I'd go primary/secondary with a thermostat and very small circulator (maybe a Taco 003) for each room, and an indirect tank for your hot faucet water. Dan wrote about such a system a while back which worked great. That one used two smaller boilers instead of one large one, which allowed one to still operate even if the other broke down. I like that kind of redundancy.

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imatellerslie

sorry, misfire

imatellerslie

Based on the help I've gotten here, this is what I'm considering

The radiators seem to be big enough to heat the house with 120 degree supply water in all but the worst conditions. I will put in a small boiler to supplement the geo at those times. The rad temp will have to go up when the outside temp falls too low for the geo to do the job, so I don't think I can use the boiler in conjunction with the geo to heat the radiators, because the return temp to the geo would be too high. Instead, I'll have to use the boiler alone to heat the radiators. In order to utilize the geo in the really cold weather, I'll have to put in an air handler in the basement for the first floor, and a high velocity system in the attic for the second floor, with a water coil from the geo in each. That way, the geo can provide A/C, and it can also provide heat in the winter, either by heating the radiators, or heating the air while the boiler heats the rads. Now...how to plumb it...

Wayne_12

Econar

There are ways to utilize a ground source heat pump with a hot water system. Depending upon the manufacturer, 130 degrees is pushing the limit. Isolate and lockout the heat pump from the boiler when the boiler is used to heat above 120/130 degrees.

I commend your persistance to explore geo thermal when so many advisors are against the idea of using the ground as a source of heat, based simply on cost.

There are programs out there that will allow you to enter your projected operating costs of the various fuels and then compare the savings of using geo thermal. Many times the home owner can purchase the geo thermal system and still have additional money left to make a larger payment or add ammenities to the building.

My personal feeling would be to use a system that has a glycol and water as the heat transfer medium. Geo pipe is a plastic pipe buried in the ground. Filled with antifreeze and water. The heat pump in the building removes btu's of heat from the loop field and then transfer the heat into the water system used to heat the house.

Comapred to systems that use copper lines buried in the ground and filled with refrigerant. Copper will deterierote in certain soils within ten years. (Propane gas experience.)

You have done some research to realize the benifits of remote air handliers with water coils to both heat and cool the house. A heat pump is also a good choice for dehumidification of the basement.

WD

Wayne_12

Econar

There are ways to utilize a ground source heat pump with a hot water system. Depending upon the manufacturer, 130 degrees is pushing the limit. Isolate and lockout the heat pump from the boiler when the boiler is used to heat above 120/130 degrees.

I commend your persistance to explore geo thermal when so many advisors are against the idea of using the ground as a source of heat, based simply on cost.

There are programs out there that will allow you to enter your projected operating costs of the various fuels and then compare the savings of using geo thermal. Many times the home owner can purchase the geo thermal system and still have additional money left to make a larger payment or add ammenities to the building.

My personal feeling would be to use a system that has a glycol and water as the heat transfer medium. Geo pipe is a plastic pipe buried in the ground. Filled with antifreeze and water. The heat pump in the building removes btu's of heat from the loop field and then transfer the heat into the water system used to heat the house.

Comapred to systems that use copper lines buried in the ground and filled with refrigerant. Copper will deterierote in certain soils within ten years. (Propane gas experience.)

You have done some research to realize the benifits of remote air handliers with water coils to both heat and cool the house. A heat pump is also a good choice for dehumidification of the basement.

WD

RELY

Radiant geo

Have you looked into radiant heat w/geo ? look at Water furnace I think they make one.You could heat the house with radiant and still cool it from the same source.Install the boiler as a backup heat source for those real cold days and keep the look of a historic house

imatellerslie

costs

Thanks for the reply Wayne. I have looked at costs for different heating options, and that's why I'm so hard over on using geo for this house. My calculations assumed COP = 3.5 for geo, HSPF = 7.5 for an air/air heat pump, and 90% efficiency for gas. Assuming worst case heat loss (10 degree days), based on a detailed Manual J I did, and using local electricity and gas costs, I came up with these numbers: Cost to heat with:
Gas: $832/month
Standard Heat Pump: $604/month
Geothermal: $134/month

It's a no brainer.

imatellerslie

Spreadsheet to determine rad output & heat loss vs temps

I made up this spreadsheet to see how different variables affect my house. I tried to annotate my assumptions clearly. The green areas can be changed to see how the house responds. If you have a spreadsheet program that can work with excel files, check it out.

imatellerslie

Thanks for the response. I'm considering using the existing radiators in the house. I know they'll provide very comfortable heat. I just need to find out about the available geothermal heat pumps that work with hydronics.

Paul Bock_2

If you can get most of the heat

you need out of the radaitors,and your planning to install hi v with chilled water anyway, make the hi v the second stage and do away with the boiler entirely. I have yet to have to install a boiler for back up on a geo system, and I've heated some real barns and some really well constructed buildings. The heat pump has to be sized for the heat loss of the building, so all you are lacking is enough emitter surface at the required temp on a design day. if the coils in the hi v's are big enough to cool the space, they should be able to heat it as well. I wouldn't put in a boiler unless you really want the system rendundancy. Paul

Paul Bock_2

diversity does play an important role.

look into installing a buffer tank to de-couple the primary loop from the heat pump loop - it gives you some thermal mass to work with, and then look into staging two or more smaller tonnage heat pumps together to get to the required heat loss. why run a 5 ton if you don't need 5 tons all the time? Paul.

imatellerslie

decoupling

I have been giving a lot of thought to the piping for this system, and was planning to use a tank as you mentioned after reading one of the things Dan wrote on here. I have never seen one of these tanks, and have no idea where I would get it.

I thought most geothermal units were staged with multiple compressors. I wouldn prefer to have a system that can match output to demand to minimize cycling.

imatellerslie

COP

I noticed on the Econar site that COP goes way up when supply temp on their hydronic geothermal units is lowered. Playing around with the spreadsheet, I found that I can lower rad temp to 90 degrees when the temp outside is 40 and still make enough heat from the rads to keep the house at temp. If I used several smaller geo units and staged them, would this make the efficiency higher? Intuitively it seems like it should. Thoughts?

Paul Bock_2

one source for a buffer tank

would be vaughn manufacturing. They make sepco lined tanks, at www. vaughncorp.com. My experiance with watersource heat pumps is that up through 5 tons or so they only have one compressor stage - we use climate master- so we usually stage smaller ones together. i'm not familiar enough with water furnace or florida heat pump to say how many stages their smaller tonnage units have. Paul

imatellerslie

How much does it cost to

buy smaller ones and stage them, compared to buying one large unit?

Thanks for the help Paul.

Paul Bock_2

Thats a question I can't

answer. I know that due to the limited tonnages available from most manuf. we usually wind up staging a couple or sometimes more together to get the load. cast iron radiators work partly by convection,and partly by radiant energy. when you put 90° water through them you won't get much convection, so you are going to have to adopt a control strategy that incorporates constant circulation to get any heat out of them at that water temp. Paul

imatellerslie

I calculated my radiator output based on the EDR of each radiator. I agree with you that most of the output will be radiative at low temps, with very little delta T between the radiator and air to drive convective air currents. I will probably put some sort of reflector behind the radiators if I can find something aesthetically appealing.

Thanks for the response!

Paul Bock_2

ahhh, it depends

No seriously, I install, so jobs already have a price when they come to me. but you are going to have redundant piping and wiring and controls. I can tell you that starting one big heat pump all the time on a single phase service can really make the lights dim if your electrical distribution system is marginal. If you go with the boiler you will wind up with some rendundant componants as well as some componants you wont require for the heat pump like low water cut off, thermal switchs, and fuel storage. Its just some food for thought and I hope you find somthing you can use in all of it. Paul

imatellerslie

I had another thought re: your last post in this thread

I planned to split the house into 5 zones, with each zone covering several adjacent rooms on the same floor. Each zone's circulator will be controlled by thermostat centrally located near those rooms (hallway). And the radiators in each room will be controlled by a TRV. I expect that the thermostat will just keep the circulator running until it's satisfied. The temp supplied to the radiators will only lower if I set the geo to run based on the delta-T from its supply & return, so that its heat output is matched to the house. The other method is for me to set the geo to run until a high limit is satisfied, but that won't allow me to take advantage of the higher efficiency given by going to the lower temp. Thoughts?

imatellerslie

I would like to stage the geo units if it's

economically feasible. I know most of the cost of this system will be in putting in the ground coupling, however, if it costs several thousand more to buy 2 2.5 ton units rather than one 5 ton, i'll probably go with the 5 ton and rely on the buffer tank to minimize cycling. As far as the electrical distribution, I need to totally update the electrical in this house and was planning on a 400A service.