System not heating up

[AMontemagni]

By the suggestion of a licensed HVAC tech, I installed check-valves into both Zones of my heating system to prevent 'ghost-flow' from happening when one zone is on. Since then, when I start the system, it will take 1 to 1 and 1/2 hours to heat up the entire zone. And by then the first room it heats gets up to 75-80 degrees, whereas the last room is just hitting 70 degrees.

The temperature of the boiler is fine.

I have bled all of the air out of the system (I believe) in both zones.

I have plenty of experience soldering so I do not think there is an obstruction in the copper.

The check-valves I installed were from Lowes. They had 1 input and 1 output and the inside was that plastic piece that moves back and forth with pressure.

Please see the attached diagram. Zone 1 is the main floor of the 1500 sq. ft. ranch home, and Zone 2 is the basement. Both zones circle around the perimeter of the house.

Any suggestions (besides getting a tech in)?

[LazyPup]

When we examine the physics of water flow pressure is by far the most difficult aspect to understand. While we commonly think solely in terms of "pressure" there are a number of different pressure effects that must be considered.

First let us consider your house water distribution system. The supply pressure in your house is generated by either the municipal water main pressure or a home well pump system and when all faucetts are closed the pressure should be in a range of 40-80psi which is known as the "Static Head Pressure". Static meaning there is no flow at this point.

When a faucett is opened flow begins. As the water leaves the faucett the physical pressure of the water almost instantly drops to 'Standard atmospheric pressure". This can easily be demonstrated by holding your finger tightly against the tip of the faucett and open the faucett. You would then note the water will spray across the room but if you lower your finger as little as an inch the water will now only hit your finger and flow around it without actually spraying sidewards. The force of flow that you feel at this point is actually a result of the velocity and inertia of the water flow but the actual pressure of the water has now dropped to standard atmospheric pressure.

The actual pressure drop from the static head pressure at the source to the standard atmospheric pressure of the water leaving the faucett occurs gradually in the pipe behind the faucett, thus if we had a pressure gage on the line immediately behind the faucett it would show a pressure much less than the actual "Static head pressure" it had when the faucett was closed. This lower pressure under flow is known as the "Dynamic Head Pressure" or commonly called working head pressure.

A vertical column of water has a physical weight of .434psi per foot of vertical rise. Thus if your water enters the house in a basement and it must then be pushed up to a faucett in a second story bathroom we have approximate a 20foot vertical rise and the physical weight of the water in the riser is .434 x 20' = 8.68psi which would be a resistance or physical pressure opposing the flow in the riser.

We also must consider the friction of the water as it passes through the pipe and fittings in the system. The amount of friction is determined by the type of pipe material and the number of fittings or changes in direction in the flow. The friction loss is called "Friction Head Pressure." and is normally expressed in equivalent feet of vertical head pressure thus if the total friction loss of the pipe from your main to the faucett was .434psi it would be called "one foot of Friction Head Loss"

Thus at any point in a water distribution system the maximum available "Dynamic Head Pressure" would be the Static Head pressure minus Vertical Static Head and Friction head.

These losses can be quite substantial which is evidenced in the plumbing code tables.While the code requires a minimum of 40psi static head pressure the minimum allowable Dynamic head pressure at a shower is only 8psi while flow is occurring.

A check valve requires a fair amount of pressure differential or velocity of flow to physically hold the gate open while flow is occuring, for this reason often check valves do not function well in a hydronic heating system.

A hydronic heating system is a closed loop, therefore the pressure remains relatively constant at all points even while flow is occurring.

It is commonly believed that the circulator pump must push the water up on the supply riser side but this is not entirely the case. Since we have an equal amount of water coming down on the opposite end of the system the vertical head loss on the riser side is compensated by vertical head gain as the water comes down on the opposite end so vertical static head is self canceling.

Taking the concept of vertical static head to the next level, we must understand that water expands as it is heated and contracts as its cooled (providing it remains above 39degF at all points). Technically speaking the cooled water coming down the return side is slightly heavier than the heated water going up the supply riser. In fact, years ago it was common to rely upon this fact to create gravity flow hydronic systems that did not have pumps.

Given that a hydronic system is a closed loop, it then stands that no matter where we install the circulator pump as the pump pushes water ahead an equal amount of water is returning to the pump through the loop thus while the pump is providing propulsion for circulation the actual pressure differential across the pump is nearly zero. In fact, the only pressure the pump must overcome is the "Friction head loss" in the piping system.

Understanding that the intent of the system is to deliver the heated water to your finned radiators we should then design a pump that will propel the water at a low velocity to allow the heat energy in the water time to be radiated before we return the water to the boiler otherwise we would just be wasting energy.

The problem here is that if the pressure remains constant at all points and the velocity of flow is very low, there is not sufficient pressure differential or velocity to fully open the gate in a check valve and in many cases the check valve will produce a restriction to flow.

A much better solution is to install normally closed electrically operated solenoid valves on each zone and conncet the valve to the pump control system. In this manner when the zone pump is off the valve is closed and no flow can occur through that zone, however, when the pump is on, the valve will be fully opened and it will not introduce any resistance to flow.

[AMontemagni]

Reply to Lazypup

Lazypup,
That makes perfect sense to me....that is a great way to explain it.

Essentially, I need to now remove the check valves I installed and install the soleniod in its place. I found the normally closed soleniod at Home Depot - for $99. Are they normally that high in price?

Also, Do you I need to install one in each zone, since installing one in Zone 1 would stop all flow when Zone 1 is not functioning, so Zone 2 would operate fine? Is that correct?

[Lewelsvc]

Zone valves

I loved the explanation of Lazypup also. I am not a plumber but rather a general handyman who often has to solve or repair plumbing problems.
First the valve the HVAC recommended was a Flo-Chek valve not a check valve to stop ghost flow. A Flo-chek valve works by a small weight rather than a spring loaded valve. There is less resistance to flow.
Second, the circulator pumps in a HVAC system normally work in a push into the boiler manner rather than a pump into the zone manner. This is to protect the boiler. If air gets into the system you don't want to pump the water out of the boiler when it is heating for it could crack the boiler. This method is less efficient pumping but more protection. Also the pump is not a positive displacement pump that builds up pressure but is a vane type like a cars water pump. This prevents too much pressure being built up when a zone valve closes or an obstruction occurs, which could blow a joint. An obstruction stops the flow even though the pump is pumping. The vane pump allows flow past it when it is off which is why you need the Flo-Chek valves to prevent gravity flow.
I would recommend the two zone valves because it gives more control of the system. The problem with one is that when zone one is on, it could induce either gravity flow or venturi flow in zone two.
Remember when connecting the zone valves that they work on 24 volts and not the 120 volts the pumps work on. Connect to the control circuit, not the power circuit or you will fry the solenoids.
Good luck. I hope this helps some.