DPS thermal store DHW performance

[johnsville]

Danfoss, Oventrop, etc, make TMVs with remote temperature sensors. Sense the DHW outlet temperature and have the modulating valve body on the outlet of the PHX. One port to the bottom of the cylinder,the other to the inlet of the PHX. The pump is located between the PHX and the valve body. It circulates on itself through the PHX. To maintain the DHW outlet temperature the valve opens slowly sending water to the bottom of the cylinder. This way it only draws from the cylinder the right amount of hot water. Some makers modulated the pumps to do the same thing. I think Gledhill did that. You could have bought one of their pcb boards and the sensors and the right modulating pump. I do not know the cost of the pcb.

Ah, useful information - didn't know about the modulating controller, but I guessed the valves might exist. My cunning plan was to combine exactly that sort of arrangement with a second PHX. The second PHX goes between the primary and the bottom of the store/cold mains in. The idea is that the hot outflow from the primary exchanger is chilled by the incoming mains so it's completely cold before going in the bottom of the store. Without it, although the flow rate is directly proportional to DHW flow rate, it's still a hot return to the bottom of the store.

Having the PHX inside the top of a cylinder gives clear advantages. The whole of the plate is preheated by the mass of hot water. Have the cold water main pipe enter the cylinder at the bottom. It continues up to the PHX. Out of the PHX and top the top and out to a TMV and to the taps.

The primary side of the PHX has a pipe to the top of the cylinder and open. The bottom go to the outside at the first point. It then runs to a pump. Then from the pump to the bottom of the cylinder and back inside again.

A flow switch is on the cold mains pipe. A thermostat fitted on the pipe of the DHW outlet from the cylinder. When there is flow and the temperature is below 55C (or whatever) the pump is held off. The preheated PHX and the preheated DHW pipe inside the cylinder may be enough to supply small low flow water demands. Once the DHW temperature drops because the DHW flow is too high, the pump cuts in to pump hot water through the plate. The bigger the plate the better the operation and the less a pump will be cutting in.

 

[Norcon]

Welcome back to the forum johnbigwatersystemsburnerville.

You didn't mention that having the plate inside the store leaves it vulnerable to having a shed load of scale cooked unto the plates as happens with immersed coils.

The plates may flex but would it be enough to ward off scale build up?

DPS seem to have went down the same path as gledhill from what I can tell. Hardly inspires confidence with the product.

 

[johnsville]

Welcome back to the forum johnbigwatersystemsburnerville.

I have only been away a few weeks and only on the electric forum.

You didn't mention that having the plate inside the store leaves it vulnerable to having a shed load of scale cooked unto the plates as happens with immersed coils.

The plates may flex but would it be enough to ward off scale build up?

Scale build up in square PHX's is far less as the plates flex more.

DPS seem to have went down the same path as gledhill from what I can tell. Hardly inspires confidence with the product.

I don't know much about this company, but both are still trading. TVR went bust so should have no confidence in cars as well? Many companies that make thermal stores are still trading.

 

[silverback]

"Having the PHX inside the top of a cylinder gives clear advantages. The whole of the plate is preheated by the mass of hot water."

Really? how do you work that out, do you uinderstand the makeup of a plate heat exchanger, the mass of water will only be in contact with the outer plates and the sides, that would equate to probably 20% of the surface area

 

[johnsville]

"Having the PHX inside the top of a cylinder gives clear advantages. The whole of the plate is preheated by the mass of hot water."

Really? how do you work that out, do you uinderstand the makeup of a plate heat exchanger, the mass of water will only be in contact with the outer plates and the sides, that would equate to probably 20% of the surface area

Do you understand conduction? All the water, primary and secondary, in the whole plate will be heated by the body of primary water around it. Heat loss from the plate is zero. That is pretty obvious.

 

[silverback]

"Having the PHX inside the top of a cylinder gives clear advantages. The whole of the plate is preheated by the mass of hot water."

Really? how do you work that out, do you uinderstand the makeup of a plate heat exchanger, the mass of water will only be in contact with the outer plates and the sides, that would equate to probably 20% of the surface area

Do you understand conduction? All the water, primary and secondary, in the whole plate will be heated by the body of primary water around it. That is pretty obvious.

But as I have said all along that is not how a plate heat exchanger is designed to work, the exchange occurs plate to plate
At the end of the day, you believe what you want and I will believe what I want, I doubt that either will change their opinions, but I have installed hundreds of heat exchangers all over the world and never once has one been inside the store, so we will have to agree to disagree, as I am sure both of us have better things to do then squabble about this.

 

[johnsville]

"Having the PHX inside the top of a cylinder gives clear advantages. The whole of the plate is preheated by the mass of hot water."

Really? how do you work that out, do you uinderstand the makeup of a plate heat exchanger, the mass of water will only be in contact with the outer plates and the sides, that would equate to probably 20% of the surface area

Do you understand conduction? All the water, primary and secondary, in the whole plate will be heated by the body of primary water around it. That is pretty obvious.

But as I have said all along that is not how a plate heat exchanger is designed to work, the exchange occurs plate to plate
At the end of the day, you believe what you want and I will believe what I want,

I have the impression you are taking the mick or not that bright. We all know how PHX's work. They also, lose a lot of heat unless the they are insulated.

Immersing them in primary water that is 70C to 80C will preheat the PHX. That is obvious. Small flows and demands of DHW need not have the pump running using the preheated water in the plate and associated DHW pipes inside the cylinder. Efficiency is high as heat normally lost to the air is not lost at all. The packaging is also far superior, giving neat cylinders with few parts hanging off them. All this I have been previously explained to you.

I don't do opinions, I go on facts. A proper engineer could look at it and easy assess, as thermal store makers have. Because you have never come across or heard of it does not mean it does not work or exist.

I did a Google and this was easy to get up. A plate inside a cylinder.
http://www.nu-heat.co.uk/core/media/media.nl?id=1371&c=472052&h=4ebe53df67820adf2817&_xt=.pdf

http://www.nu-heat.co.uk/s.nl/it.I/id.706/.f

The only one squabbling is you.

 

[silverback]

Nu-Heat, not the best UFH in my opinion, so I would not rate their stores persoanlly.
You go on facts, what sorts of systems do you install using Plate Heat Exchangers?

 

[johnsville]

Nu-Heat, not the best UFH in my opinion, so I would not rate their stores persoanlly.

The point is the PHX inside the cylinder., not their UFH.

You go on facts, what sorts of systems do you install using Plate Heat Exchangers?

Facts of heat loss, efficiency, smaller packaging, etc.

 

[silverback]

"Facts of heat loss, efficiency, smaller packaging, etc"


That is a fact that is stated by Nu-Heat, how many have you installed to prove that fact, what a manufacturer says to what the product actually does are two totally different things

 

[Norcon]

Installing them wouldn't prove jack.....

As the internal plate is encapsulated within the store of heated water then its losses are equivalent to the capacity of space the plate displaces in heated water which is lost through the cylinder wall.
It will be a lot less than an external plate, though still not be a significant amount.

Though you could argue its losses are very close to zero as the plate temp is always close to the store temp.

 

[johnsville]

"Facts of heat loss, efficiency, smaller packaging, etc"

That is a fact that is stated by Nu-Heat,

and others and any "engineer" who knows his stuff. It is clear you fit what others have designed. If you cannot see that a PHX loses less heat inside a cylinder then maybe you are in the wrong game.

 

[johnsville]

Installing them wouldn't prove jack.....

As the internal plate is encapsulated within the store of heated water then its losses are equivalent to the capacity of space the plate displaces in heated water which is lost through the cylinder wall.
It will be a lot less than an external plate, though still not be a significant amount.

Though you could argue its losses are very close to zero as the plate temp is always close to the store temp.

Ever opened a cupboard with an unlagged plate inside? They lose quite a bit of heat as the heat inside will confirm.

Having an internal PHX and an internal pump would mean no check valve and even more efficiency, and even better cylinder packaging.

 

[silverback]

Installing them wouldn't prove jack.....

As the internal plate is encapsulated within the store of heated water then its losses are equivalent to the capacity of space the plate displaces in heated water which is lost through the cylinder wall.
It will be a lot less than an external plate, though still not be a significant amount.

Though you could argue its losses are very close to zero as the plate temp is always close to the store temp.

Ever opened a cupboard with an unlagged plate inside? They lose quite a bit of heat as the heat inside will confirm.

Having an internal PHX and an internal pump would mean no check valve and even more efficiency, and even better cylinder packaging.

PHX will only lose heat when the PHX is in use, they are instantaneous, so they do not suffer from standing heat losses, so I think the heat loss saving is very small

 

[johnsville]

The heat loss is big enough. It also gives great packaging, which is needed in domestic appliances. The PHX, and associated DHW pipework (this can be 28mm inside to give a larger volume of preheated DHW) inside the cylinder, is also preheated. With a DHW PHX and pump "inside" a cylinder a check valve is not needed. Heat loss from the pump is captured inside the cylinder. Having the CH pump inside also captures wasted pump heat

Understand what is being put across, as all I am doing is repeating myself to you.

Thermal storage and thermal systems in general are vastly misunderstood by the average plumber.