Dynamic Behaviour of Thermostatic Radiator Valve (TRV)

DHexpert

I have a new task about thermostatic radiator valves and have difficulty in finding the dynamic behaviour of the thermostatic radiator valve. In detail: I can find the kv value for the set values (the numbers on the TRV) but I cannot find the change of kv (the opening change) as according to the indoor temperature at any time. In another words, I need to find what the flow will be at different set values of TRV (for example the no 3 that is in between 1 and 5 numbers) and at different indoor temperature conditions (for example at start up of heating the indoor temperature will be 10degreeCelcius together with during the continuous operation control dynamics of TRV).
The technical specifications by the TRV producers do not include this (kv or flow change) at partial behaviour conditions according to the set number values, right? If not, how can I find this relationship (kv according to TRV set no and indoor temperature value during operation)?
Regards.

Jamie Hall

I haven't done a study of this, but... by "set value" I presume you are referring to either the target temperature or to the maximum opening allowed.

A TRV will be open to the maximum allowed setting at some point below the target temperature. As the target temperature is approached, the TRV will close. Depending on the specific valve and sensor combination, the closing may be slow, and take place over a moderate range of temperatures below the target temperature. Other valve and sensor combinations may show a sharp close -- that is the valve stays fully open until the target temperature is reached, and then closes quickly on a further rise.

Similarly, the valve may open quickly on a drop (but typically at a slightly lower temperature than that at which it closed -- referred to as hysteresis) or may open slowly as the temperature falls.

The quick opening/closing style will tend to keep the temperature in a rather small dead band at the target, depending on the hysteresis. The slow opening style will tend to keep the temperature constant, but at a value somewhat -- usually slightly -- below the target, as it modulates.

Don't know if that helps...

DHexpert

You described perfectly the logic of operation at the thermostatic valves. I need detailed technical specifications of the kv values as a list (or a relation expression) for different openings (in fact for different indoor temperature values during operation) at different setting of the TRV. The technical specification documents by the suppliers are not provided with the change of kv during operation for different indoor temperature values. Am I wrong (or missing something: that I am asking you if I am)?
Regards.

Zman

I think that you are looking for a chart or curve which defines the "Valve Authority" characteristics. They are usually easy to find for larger commercial valves.
You might contact the manufacture and see what they have.

DHexpert

Here is the one that I could find (I will base on this for now): (the picture below::) valve characteristic for changing differential pressure load on the thermostatic valve while (what I need for other parameters as well) showing the flow correspondance at different indoor temperature (sensed temperature). I guess that there is no available data as this given by the thermostatic valve producers, Right?

The picture ref is Energy Simulation in Building Design

Thank you for your time Zman and Jamie Hall.

Jamie Hall

That chart would be for a valve which opened on rise, such as might be used in a cooling system. TRVs used in heating systems are close on rise -- but will do much the same sort of thing, only reversed.

You would have to find the curve from the manufacturer, and it will be different for each model of valve.

Interesting that delta P across the valve is more or less proportional to the square of the flow -- more or less! -- for a given T. Not surprising -- it should be.

My curiousity is terrific -- what are you working on?

DHexpert

Checking the performance of the in-house heating units operating with different control algorithms at district heating level. So pure dynamic response is a must especially by the thermostatic valve for changing conditions and also by the other parts i.e. radiator.
Getting performance data from the manufacturers is annoying all the time; either they don't provide or they give something not related to the request or total silence but best is saying that they are busy. But tomorrow I will try to ask the valve characteristic data/figure from some. Because each setting on the thermostatic valve has a direct effect on the valve opening. then according to that setting; adjustment of the further openings base on the preliminary opening by the setting. Also, p-band can be adjusted which has another influence on the valve characteristic, I assume.

Any new idea, info: please share with me.
Regards.

Paul48

How could they chart the flow characteristics without knowing the pump characteristics? And, if they could, why would that be important to them? Better question.....why is it important to you?

DanHolohan

I'm fascinated. May I ask where the district heating is?

Zman

Paul48 said:

How could they chart the flow characteristics without knowing the pump characteristics? And, if they could, why would that be important to them? Better question.....why is it important to you?

It should be important to everyone in hydronics.
Check it out...

Harvey Ramer

Caleffi publishes the information you are looking for, for their TRV's. http://www.caleffi.com/usa/en-us/catalogue/radiator-valve-body-angled-220302 In the technical document. It lists the CV ratings for all the numbers on the proportional pressure band.

Paul48

@Zman
Obviously I wouldn't have asked, if I understood the need to know the intermediate flows. I don't believe it is something that has been discussed here, before, as it relates to TRV's. I don't recall anyone ever warning folks to beware of intermediate flows when they have recommended TRV's to other people. Anyway........what would you suggest I "check out"?

Jamie Hall

Paul48 said:

@Zman
Obviously I wouldn't have asked, if I understood the need to know the intermediate flows. I don't believe it is something that has been discussed here, before, as it relates to TRV's. I don't recall anyone ever warning folks to beware of intermediate flows when they have recommended TRV's to other people. Anyway........what would you suggest I "check out"?

That Caleffi document (thanks, @Harvey Ramer !) is interesting. It wouldn't apply, I think, to remote electrically controlled units -- but it is fascinating to see that there is a real range of control there with the liquid filled controllers.

Zman

Sorry,
The brilliant Robert Bean article did not post.
Let me try it again.

DHexpert

Paul48 said:

How could they chart the flow characteristics without knowing the pump characteristics? And, if they could, why would that be important to them? Better question.....why is it important to you?

The system pressure loss is based on the pressure loss coefficient (known as kv or cv both same - SI or USA) of the pipe branches and the other equipments such as valves, meters, bends etc. regardless of the flow. However for thermostatic valves (or any other proportional valves) this kv (or cv) is changing since the opening of the valve changes according to its control logic during operation. This is what I am looking for - the dynamic behaviour of thermostatic valve changing according to the pressure head through it, the sensed temperature, and set temperature setting. The balance point of operation has to be considered with the pump characteristic together with the system pressure loss.
Why important? This small thermostatic valve has a significant effect on the rest of the district/central heating network. Understanding its mechanism can be rewarding in efficient solution of the rest in one or more way.

DHexpert

DanHolohan said:

I'm fascinated. May I ask where the district heating is?

I am a researcher working in the field of District Heating. So far I have dealt mainly the distribution piping network but this new task of mine has the focus on the housing section considering the control, radiator, domestic hot water. There is not a specific case but the general situation in most district heating systems. Any idea for a case based future project idea funded by H2020 or any other funding organization, let's discuss together.

DanHolohan

Are you familiar with DBDH? They may have this information.

http://dbdh.dk/magazine-archive/

Jamie Hall

DHexpert said:

... This is what I am looking for - the dynamic behaviour of thermostatic valve changing according to the pressure head through it, the sensed temperature, and set temperature setting. The balance point of operation has to be considered with the pump characteristic together with the system pressure loss.

If you look through the Caleffi technical documents on the operation of their TRVs, you will note that the drive system for the valve opening uses an incompressible fluid operating against a powerful spring. Thus the valve opening -- and hence the Kv value for the valve -- is not a function of the pressure head through the valve, any more than it would be for a mechanically actuated valve. The head loss through the valve is strictly a function of the flow and the valve opening. The latter, in turn, is strictly a function of the set point of the controller and the temperature of the space.

Or to look at it another way, the dynamic behaviour of a thermostatic valve of that type is no different from the dynamic behaviour of any other valve.

For any given combination of set point and space temperature there will be one, and only one, valve opening condition, and thus fixed relationship of flow and pressure drop.

Now if one is considering an hydraulic system containing a number of these valves, controlling in series some radiation, and fed in parallel from some network of pipes and a pump or pumps -- as it might be in a district heating system or even in a single building -- the situation becomes involved, and constantly changing as the space temperatures change (or people change the set points!). Can it be computed? Of course. Being somewhat lazy, my approach would be to compute flows and heads for only a very limited range of cases, however.

DHexpert

Harvey Ramer said:

Caleffi publishes the information you are looking for, for their TRV's. http://www.caleffi.com/usa/en-us/catalogue/radiator-valve-body-angled-220302 In the technical document. It lists the CV ratings for all the numbers on the proportional pressure band.

What they provide is the kvs value (kv value when the valve is fully open) as usual by all manufacturers. What I need is the kv change figure (expression) as according to the sensed temperature. The figure in my previous post is exactly what I need but I need another detailed expression including the effect by the set values on the valve (some tech specs give this info by showing the kvs value for each number set on the valve) together with the effect of the pressure head through the valve and also the supply temperature to the radiator.

DHexpert

Jamie Hall said:

DHexpert said:

... This is what I am looking for - the dynamic behaviour of thermostatic valve changing according to the pressure head through it, the sensed temperature, and set temperature setting. The balance point of operation has to be considered with the pump characteristic together with the system pressure loss.

If you look through the Caleffi technical documents on the operation of their TRVs, you will note that the drive system for the valve opening uses an incompressible fluid operating against a powerful spring. Thus the valve opening -- and hence the Kv value for the valve -- is not a function of the pressure head through the valve, any more than it would be for a mechanically actuated valve. The head loss through the valve is strictly a function of the flow and the valve opening. The latter, in turn, is strictly a function of the set point of the controller and the temperature of the space.

Or to look at it another way, the dynamic behaviour of a thermostatic valve of that type is no different from the dynamic behaviour of any other valve.

For any given combination of set point and space temperature there will be one, and only one, valve opening condition, and thus fixed relationship of flow and pressure drop.

Now if one is considering an hydraulic system containing a number of these valves, controlling in series some radiation, and fed in parallel from some network of pipes and a pump or pumps -- as it might be in a district heating system or even in a single building -- the situation becomes involved, and constantly changing as the space temperatures change (or people change the set points!). Can it be computed? Of course. Being somewhat lazy, my approach would be to compute flows and heads for only a very limited range of cases, however.

I need to model old thermostatic valves which base on gas or wax fill (instead of this incompressible fluid), the increase of the temperature of this fill medium heated up by the ambient (sensed) temperature and hence expand meanwhile weighing on the spring which as result close the valve opening. In one of the article, it stated that change of pressure head (differential pressure load) in the closed pipe circuit influence the valve characteristic. This is also in consideration by TELL thermostatic radiator valve labelling system (Ref: http://www.tell-online.eu/classification/index.html) and also the figure in my previous post proves the same. May be the models by Caleffi, since they are using incompressible fluid, can be more stable to changing differential pressure on them. But as you can see in the figure that I posted, the influence of the differential pressure cannot be omitted for the old thermostatic radiator valves.

Another consideration by the TELL thermostatic radiator valve is the water temperature on the valve characteristic. The inner expanding/adjusting medium in the thermostatic radiator valve, since expanding comes true with temperature change, can be influenced by the supply temperature to the radiator. This can cause un-wanted overheating.

To be sure (let's discuss together): when the setting number of the valve is changed manually by the consumer the pre-level of the valve is set to a specific distance (a defined gap as the valve opening). The indoor temperature (as sensed temperature) leads to adjustment of the opening starting from the pre-level by the setting number. Cold indoor temperature cause a large opening while warm but still less than the set-point level indoor temperature cause a small opening. So this response characteristic (the output reaction according to the input) is one of the main feature that one can need. The relatively high differential pressure can influence the load balance of the inner valve mechanism so the valve characteristic can change. Same applies for the supply temperature from the district heating network: the influence of this temperature in the fluid expanding property can change the valve characteristic. The differential pressure affect the pre-level of the opening due to change in the load/s on the spring, which causes a change of the kvs value at full opening (deviating from the pre-setted level). That is why most house stations are equipped with differential pressure regulator limiting the pressure difference at a specified level. Supply temperature change also leads to a change of the valve opening (pre-leveled by the manual setting) since the extra temperature increase (due to high supply temperature), this time, results in more closing of the valve than the low temperature case due to extra expansion of the inner fluid medium.

So such parameters cause a shift of the valve characteristics by causing a changed kv value even at full opening conditions, these full openings (at the mechanism of thermostatic radiator valve) are partial openings at differing setting numbers).

Jamie Hall said:

For any given combination of set point and space temperature there will be one, and only one, valve opening condition, and thus fixed relationship of flow and pressure drop.

Let's talk about the ideal case: the thermostatic radiator valve adjusts the flow in order to maintain the set indoor temperature. The adjustment of the flow comes true by local change of the opening during the operation of the thermostatic radiator valve (whatever the manual set point is). So the kv value (not kvs this time) changes in each change of the valve opening (since the flow duct is become narrow by the thermostatic self actuator (fluid expansion) as according to the error between the sensed indoor temperature and the set-level). This is out of fixed relationship that you mentioned. May be I am wrong so I am asking. This change of relationship during the normal operation, that is changing kv value (or cv value) is missing in the technical specifications by the manufacturers. Or I can't reach it due to wrong search keyword use by me. The graph that I showed in my previous post is exactly showing what I need. But I need to find also the effect coming from the water temperature (more proper, supply temperature from the district heating network).

Jamie Hall

It would, of course, be perfectly possible to develop a model of the operation of a thermostatically controlled valve which took into account the variables -- such as the senstivitiy of the control medium to temperature, the control mechanism, the response of the control and valve seat to variations in total pressure and pressure differential, sensitivity to installation configuration... and whatever else one might think of. Whether it would be of general interest is another question entirely. Frankly, from the standpoint of process control, I doubt it. It is the sort of question which, were I still teaching engineering, I might set for some Master's candidate -- and integrating the resulting model into a model of a complete system would be a nice task for some Doctoral candidate!

DHexpert

Thanks Jamie Hall for your time and explanation. It was great to discuss with you and all other. I need to evaluate different realistic cases with different control approaches. Also, in some cases, I encountered/felt overheating at some spaces (heated with radiator) that I guessed the reason being due to supply temperature increase by the source. Thermostatic valves obviously have saved lots of energy so far. Detailed model that can simulate both the old ones and the new ones can be rewarding.
The kv change during the operation at different valve manual set value, different p-pand, differential pressure, and supply temperature is a perfect aim seems to be for now but can be simplified in case of non availability of data.

DHexpert

I wanted to share the latest info as answer to my question at this post of mine.
Here is the technical specification by the oventrop: https://www.oventrop.com//Pools/Files/hbtd/en/db_1183763_en_251a7c48-4ad6-4264-9822-1460fc46a5be.pdf

The description for p-deviation is "the difference between the thermostat setting and the actual space temperature".

Hence the tables showing the kv values for different p-deviation levels at different thermostatic radiator valve setting number are the ones that I asked for at this post. But not covering all of my need for the modelling! Still looking forward for any comments/publications regarding this issue by you.

In this tech spec by Oventrop: there is a term as 'Zeta at P-deviation'. Any idea what it is?
Regards.