I think you're talking about Danfoss radiator valves.
You can use them on a radiator train, but you can't really use them for individual room control because they work by restricting the flow of hot water through the radiator. So, if you turn down the heat on an upstream Danfoss radiator valve, every radiator downstream of that one will be restricted to that temperature or less.
That is, how can you get a flow of 2 gallons per minute through a downstream radiator when a valve upstream of it is limiting the flow to
1 gallon per minute?
I've had experience with both Danfoss valves that don't require any power and Honeywell 24 VAC zone valves, and the Honeywell is definitely the way to go... more expensive, but well worth it in the long run.
That's an interesting issue that I've never heard discussed before. I even recall seeing Richard Trethway on This Old House putting one in for a customer. But there was no discussion of what happens to the downstream radiators. These are widely used in Europe. What do they do? It would be easy to have a two port valve, where if the temp set is reached, the water goes out the second port that bypasses the radiator and sends it on it's way down the rest of the loop. But the ones I've seen, I don't recall it being anything other than a simple valve that blocks the flow of water. So, as you say, once it shuts off the water, all radiators further downs stream are screwed. So, how does this actually work?
I would think STEAM radiators would be connected in parallel, but hot water based ones? Why would they be connected any differently than baseboard ones?
Cast iron baseboard radiators that carry hot water will be connected in series within each apartment. They have to be because that apartment's thermostat controls the zone valve that allows hot water flow through the radiator train in that suite.
The radiator trains in every apartment are connected in parallel. They have to be so that each apartment can recieve heat independant of all the other apartments.
How would it be if the radiators in an apartment block were all connected in series so that all of the output from the primary pump would go through suite 1, then Suite 2, then Suite 3, and so on until you got to Suite 22. Suite 1 would get hot and so they'd turn their thermostat down and that would stop the flow through the entire building.
It's series connections within each apartment radiator train, and all the apartment radiator trains are all connected in parallel.
In a house, _one_would_expect_ that the radiators in each loop would be connected in series, and all the loops would be connected in parallel as Bud says cuz it only makes sense to do it that way.
However, it's only recently that zone valves became commonplace in houses. Until about 20 years ago, most houses simply had a gate valve on on all but the longest radiator loop. They used gate valves instead of globe valves because they offered less resistance to flow AND there were no internal parts (like washers and screws) that could come out and screw up the heating system. Those residential gate valves were called "balancing valves", and the whole idea was to close the gate valve on the shorter loops, thereby forcing more water flow through the longer radiator loops. The idea was to have the same amount of water flow through each radiator loop to provide for uniform heating throughout the house.
PROPER balancing valves will have pressure taps on both the upstream and downstram ends of the valve. They sell pressure gauges that allow you to connect a pressure gauge across the balancing valve to measure the pressure drop across it. You then open or close each balancing valve until you have the same pressure drop across all balancing valves, and that means there's the same hot water flow through each balancing valve for uniform heat distribution in a house. But, as I say, years ago the plumbing contractor would just use $4.99 gate valves and guestimate when the flow through each loop was about the same, and then put the new homeowner in charge of doing the fine tuning.
The radiators in my house are connected in parallel. From what I have seen of the exposed piping in other houses, those houses were in parallel. Most (all?) radiators I have seen have balancing valves on them - multiple valves don't work so well if they are in series.
Radiators have a lot more thermal capacity than baseboards, and take far longer to heat up. In a series connection, the last radiator would just be starting to heat when the first one was hot.
Everything I'm talking about refers to hot water heating.
I know squat about steam heat.
In hot water heating, all radiator loops in a house or commercial building will be connnected in parallel, and the radiators in each loop will all be connected in series.
You achieve uniform heat distribution throughout the house when the flow rate of hot water through each radiator loop is the same.
Since some radiator loops are shorter than others, it's common to compensate for their lower resistant to flow by installing balancing valves in those loops. The balancing valves can be partially closed to pinch off flow through the shorter loops, thereby increasing flow through the longer loops.
Balancing valves aren't needed when each radiator loop is controlled by a zone valve, as in the case of an apartment block. Radiator loops with zone valves maintain a comfortable temperature by having the zone valve controlled by it's own thermostat. It's only when you have one thermostat for multiple radiator loops that you need balancing valves to ensure uniform heat distribution throughout the house or commercial building.
The above is true for HOT WATER heating systems. I don't know anything about steam heating systems.
Not only that, but even when the heat was up for hours, if the radiators were in series, it's not like Xmas tree lights. The first radiator would emit a lot more heat than the 2nd which would emit more heat than the 3rd. I don't know numbers ,but say the water temp was
160 going into the first radiator, and 140 coming out. Then 140 going into the 2nd and 120 going out. And 120 going into the 3rd radiator. I wouldn't expect much heat from that one, or any beyond it.
In parallel, it would be 160 going into all of them and maybe 140 coming out. They could have a zone valve in the main pipe, before the pipe to each radiator split off, so the zone valve controlled a whole apartment.
The house I lived in in college had probably 15 hot-water radiators spread over 3 floors. My apartment in Brooklyn had steam, but it still had at least 5 radiators (the dining room radiator had been removed for some reason, but it got enough heat from the other rooms.)
That is, Xmas tree lights all glow at the same brightness, either because they are in parallel (and each bulb is designed for 110v), or because they are in series but each light has the same voltage drop, the sum of all of which is 110-120 volts. (If there are 24 bulbs, each is designed for about 5 volts.)
But hot water radiators in series are not like Xmas tree lights in series (or parallel) . For one thing, the water flow is all in one direction. There is no alternating water flow in a hot water furnace system, like there is AC current in your home's electrical system. So the hottest water gets to the first radiator in a series system. .
If two of these radiators were in the same room, it would be a little warmer on one end of the room compared to the other. But more likely, one radiator is in each room. The second room would not be as warm as the first and the third would be cooler than either.
One more difference. When electrical devices like light bulbs are in series, the same amount of electricity flows through each one, so if that is enough to light one bulb, it will light every identical bulb to the same degree. Because the flow of electricity is what does the work.
When hot water radiators are in series, the same amount of water flows through each one, but it's not the flow of water that does the worlk The water is there to transport heat, and even though the same amount of water flows through the second and third radiator, the amount of heat in that water is less and less, in each successive radiator.
It could be the flow of water that does the work. If a stream were routed to 3 flour mills in series, and the water fell from 160 feet above sea-level to 140 feet in the first one, from 140 to 120 feet in the second one, and from 120 to 100 feet in the third one, and each used the water wheel just as efficiiently, all three mills would get the same amount of energy and work out of the water. Buy that's not how hot water radiators work.
In practice, perhaps one can use hot water radiators in series. AIUI, most people want the bedrooms a little cooler than the rest of the house, for more comfortable sleeping. And if someone cooks a lot, that makes heat in the kitchen. Of course they also have these differences, and the sizes of the rooms, in mind when they put different size radiators in different rooms.
That means they could make the 2nd radiator in series bigger than the first, and the third bigger still. to make up for the water being less hot. I don't know if that is done.
Series segments are used with baseboard heat. I doubt you will ever see it for radiators.
All that assumes the baseboads are exactly matched to the heat loss in that room for the water flow rate. Differences in matching between segments can be equalized with valves.
With steam the major heat transfer is from steam condensing to water. The supply is steam and the return is water. Steam radiators have to be in parallel.
I've thought about this and I'm sure it's not done. And that or keeping some rooms colder was the only way series radiators could work. I don't think either method is used and I'm 99% sure no one has series hot water radiators.
The hot water radiators are plumbed in series in every apartment in every apartment building in every city in North America. They are plumbed in series so that when that apartment's thermostat calls for heat, it causes the zone valve in that apartment to open and hot water to flow through each radiator in the apartment; one after the other.
And, it's true that the temperature does diminish as the water flows through the radiator train, but it's not all that much. In my boiler room I have temperature sensors for both supply and return, and the difference between the water supply temperature and the return temperature will typically be between 10 and 20 degrees F.
In an apartment block, normally all of the radiators in each apartment as well as the zone valve are connected in SERIES. So, each apartment represents one radiator "loop".
However, all of the radiator loops are connected in parallel. That way, hot water will flow through all of the apartments whose zone valves are open, but won't flow through any apartment whose zone valve is closed.
It's the same thing with houses. You have different radiator loops in your house. All the radiators in each loop are connected in series, but the loops are connected in parallel.
If you have a two story house, then typically, all of the radiators on each floor are connected in series, but the two radiator loops are connected in parallel.
If you don't have zone valves on each loop, then you have to have "balancing valves" on all but the longest loop so that you can pinch off flow through the shorter loops to force more flow through the longest loop. Otherwise the lion's share of the hot water will always flow through the shortest straightest loop because it offers the least resistance to flow.
The downstream radiators in each radiator loop WILL be cooler than the upstream radiators because of heat loss along the length of the radiator loop.
Proper balancing valves will have ports on them where you can connect a pressure gauge to measure the pressure drop across the balancing valve. You open or close each balancing valve to get the same pressure drop, and hence the same flow, through each balancing valve. You don't have to bother with that if you have zone valves that are each controlled by a thermostat.
I think this needs clarification as you both may be right, sort of. Each zone is a series of radiators. Often, a two story house with have two zones, but the radiators on each zone are in series. In an apartment building, each may have its own zone, but some older buildings were still in series with only one thermostat for the entire building.
I have no idea how apartments are connected. Are you talking about baseboards or large radiators?
My radiators are parallel. Every house where I where looked much the radiators are parallel. I have never figured out a system where the radiators are in series.
None where I have figured out how the radiators are connected.
ALL the radiators I remember seeing have valves on EACH radiator. That doesn't work if the radiators are connected in series.
My radiators heat from the top down. The return pipe is not particularly hot until the radiator is hot. Connecting is series would not work. And radiators have large thermal capacity.
Baseboards have very small thermal capacity. You can easily connect baseboards in series.
Baseboards operate at a higher design temperature than radiators. (At max design output, or at equal heat out, a baseboard will be hotter.)
I have never seen ports on valves on radiators.
Are you talking about radiators or baseboard heaters? It all sounds like baseboard heaters.
There are (were?) series baseboard systems where the valve for a single unit could regulate (proportion) between water going through the baseboard or bypassing the baseboard. You can control the heat from a single unit in a series loop. Can't remember - may have been a mechanical (not electrical) thermostatically controlled valve. (But the same thing could be done with an electrically controlled valve for a single unit in a series loop.)
And the baseboards I have seen have a 'fin' across the top opening you can rotate to be open or to substantially close off the convection out the top of the baseboard. The heat output from a single unit in a series loop can be substantially lowered.
Well, I guess that radiators can be connected in different ways.
In my building, they're in series in each suite, but all the suite loops are in parallel. All my radiators are cast iron baseboard radiators.
But, I have no doubt that other people's powers of observation are equal to mine, and if they say their radiators are in parallel, then they're in parallel.
Cast iron baseboards have higher heat capacity ('thermal mass') than copper/fin baseboards, but far lower heat capacity than full size radiators. They connect like baseboards, which is different than full size radiators.
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