cheating head pressure?

[jwise87]

I know this was discussed last year in @warno 's novel of a thread, but I just wanted to make sure that I have it correct. If I raise the water level in my tank, say by the use of a pipe running 10 or 15 feet in the air to a small reservoir, that will essentially cancel out some of the head pressure on the other side of the pump?

I am planning on using an old grain bin as a wood shed so I will have the height.

 

[warno]

I don't believe you will need to go that high. My circ has quit cavitating and I only lowered it about 2 feet from where it was. I had a mishap the other day and the boiler got up over 200° and it still wasn't cavitating.

 

[maple1]

Is this an open tank? Description?

Generally speaking, 1 foot of vertical water is 0.4 psi. But it might not be that simple.

 

[jwise87]

Is this an open tank? Description?

Generally speaking, 1 foot of vertical water is 0.4 psi. But it might not be that simple.

Yeah, it will be an open system. I am going to have between 12 and 20 ft. of head (I had trouble finding equivalent lengths for all my fittings). I currently have one Grunfos 15-58 pump and will probably end up adding another in series. I don't need much flow at all because I am just running it through a single air to water exchanger. I am aware that my current flow will be around 2 to 5 gpm if I am not mistaken.

 

[warno]

You will want to make sure you have enough flow to not have a massive delta T. If you send real cool water back to your boiler you could shock it.

For fitting equivalents I use this site. It doesn't have everything but will give you some rough figures.

 

[jwise87]

You will want to make sure you have enough flow to not have a massive delta T. If you send real cool water back to your boiler you could shock it.

For fitting equivalents I use this site. It doesn't have everything but will give you some rough figures.

What is meant by shocking my boiler?

 

[warno]

What is meant by shocking my boiler?

If you send cold water back to a hot boiler it could shock the steel. Kind of like quenching hot metal. It makes weaker over time.

 

[jwise87]

If you send cold water back to a hot boiler it could shock the steel. Kind of like quenching hot metal. It makes weaker over time.

I gotcha ya. I can understand that. I welded a small piece of spring steel the other day to make a pot hanger for my dutch oven. When I was done I quenched it in the snow and after picking it back up it snapped in my hand when I barely put any pressure on it.

 

[Woodman1]

Get that danfoss hooked up then you don't have to worry about it.

 

[Karl_northwind]

typically one shoots for about a 30 degree temp drop over a fan coil unit at full speed. depending on what you have going on 2-5 gpm may be tough to get enough heat out of. 3 gpm at a 30 degree drop is 44,000 btu. how big is the unit heater you are using? if you try to run a big unit heater you may get coldish air. you may also have trouble pushing the air out of the loop with the small pump.

 

[jwise87]

typically one shoots for about a 30 degree temp drop over a fan coil unit at full speed. depending on what you have going on 2-5 gpm may be tough to get enough heat out of. 3 gpm at a 30 degree drop is 44,000 btu. how big is the unit heater you are using? if you try to run a big unit heater you may get coldish air. you may also have trouble pushing the air out of the loop with the small pump.

I am using a 19x20 exchanger. I may be wrong on my flow. When I get it hooked up in the next few days the first thing I am going to do is stick the return hose in a bucket and see what my actual flow rate is. I can always slap another pump in series.

 

[jwise87]

Finally got it plumbed up. With cold water (about 40*), it was flowing between 4 and 5 gallons per minute. Hopefully that is enough, we will see in a week or so when I get enough firewood cut to keep this thing fed.