Pressuretrols working with Heat Timers

Travis_F

I have what could be a stupid question...



I understand the concept of how pressuretrols effectively creating a cycle, turning the boiler on and off within the desired pressures when the thermostat calls for heat.



My question is how they are suppose to work with Heat Timers, which effectively do the same thing, triggering the boiler for X minutes with a 60-minute cycle based on outside temperature instead of an inside thermostat.



We are tweaking our system here-- a 6 floor 70 unit coop-- with vents, etc... The four pressuretrols are set for 5 PSI. When I lower them function with the .5 - 2 PSI range, it shuts off the boiler before the heat timers cycle ends. The pressure drops to zero and the boiler just sits before the heat timer fires it back up for the next 60 minute cycle when the pressuretrol shuts it off early.



So it seems the heat timer and pressuretrol are working against each other. What I am missing here?

SWEI

they're wired in series

so both have to be "on" in order for the boiler to fire.  How's the indoor temp?

Travis_F

yes, but how do they work together?

Indoor temp is cold when pressuretrol is lowered to 2 psi... and I understand why and that they both have to be "on"



I think what I'm getting at is a more basic question... With regular thermostat's the pressuretrol effectively creates the cycle, by turning the boiler on and off.



But that's also the point of the heat timer, right? It creates a cycle based on outdoor temp. So it seems with a heat timer the pressuretrol effectively becomes a why to protect against high pressures and not a means to create a cycle.



Is that correct?

Travis_F

When it's colder outside

and the heat timer cycle is longer the pressure usually hits 5 PSI and the pressuretrol turns off the boiler a little before the end of the heat timer cycle. When it's warmer, say in the 40s, it usually turns off at 3 PSI or lower.



So we know we have to balance the system. Some people are cold, others hot... Several of the risers have been capped and don't have any vents. There are only a few vents on the mains and they seem small. So it seems clear what needs to be done from a venting perspective.



I'm also concerned because so many have removed their radiators over the years whenever anyone complained about cold, the super just turned it up (instead of looking at venting). There are many apartments that are heated solely from the risers. Could this also be a reason for the pressure to rise, that the steam isn't condensing fast enough because there are so few radiators? The boiler is essentially oversized to the system. This is my uneducated guess.



So I was thinking once we add vents and balance the system, we can turn down the heat and add radiators where needed... Again, an uneducated guess... a little knowledge from Dan's books can be dangerous!

SWEI

if the system is well-balanced

then the Pressuretrol (and any thermostats, if they are wired in the same circuit) become in effect high limit controls.  If the outdoor-reset controlled timer is set perfectly they may never actually trip.  With the Pressuretrol set at 5 PSI, what pressure does the system have at the end of a cycle, when the timer kicks it off?

nicholas bonham-carter

tweaking the system

i think you need more than a little tweaking, if you want more comfort and economy.

what sort of system is this-one-pipe or two-pipe? most systems can run on 1 ounce of pressure per floor, plus a couple. therefore your pressure is about six times what it should be!

it sounds as though you have short-cycling on pressure rather than heat timer cycles. when the heat timer calls for heat, as a result of it's calculations based on the outside temperature, it should produce an uninterrupted bur, to fill all the radiators with steam. your system is having trouble getting the air out of the system, or the boiler too big.

perhaps you have several boilers all linked together, in which case they could be staged, so that at the start of the burn, all boilers will fire, and as the pressure rises to six ounces, the pressuretrol will cut of the lag-boiler, leaving number one to maintain the six ounces. as the temperature drops, and the lead boiler is now unable to make enough steam, the pressure will drop and number two will fire again to help keep up the pressure.

what is your location, so we can recommend a good steam pro?--nbc

Dave in QCA

Two Separate Functions

Travis, a little more information might help us understand your system.  What type of boiler do you have.  Is it an atmospheric type or do you have a power burner.  A power burner has a purge time of around 1 minute and that can effect pressure swing on pressuretrol cycling.



But, to your question as to how the Heat Timer and the pressuretrol work together, perhaps it is best to think of how they work independently of each other.



The Heat Timer does not control the burner directly, but rather indirectly, because there are other devices that may turn off the burner, such as a pressuretrol or low water cut off, etc.   What the HeatTimer does, is to issue a call for heat, then it recognizes when the steam has been established, and then it times the call for heat (steam cycle) based on the outdoor temperature and sometimes indoor sensors as well.   So the HeatTimer is telling the system how long steam should be "up", not how long the burner should run, as other things may cause the burner to cycle.



The pressuretrol is there to limit the steam pressure.  The problem with the pressuretrol is that the factory markings are seldom correct and it may take some tinkering with the control while watching the pressure gauge to get it set correctly.   If you have it set to limit pressure to 2 psi, then you would want it to re-energize the burner at about 1 psi.    If you have a power burner, the system may indeed fall to 0 before the burner lights and begins to build the pressure back up to 2 psi.   If this is the case, I would consider having the burner tuned down a little bit, but that all depends on how long it takes to build pressure in the first place.



It is possible that you may have a coincidental occurrence in which the pressuretrol trips on pressure and shuts the burner off.  Then, before the pressure drops far enough to restart the burner, the HeatTimer ends its call for heat, thus resulting in the system going into the "off" part of the HeatTimer cycle.

Travis_F

When it's colder outside

and the heat timer cycle is longer the pressure usually hits 5 PSI and the pressuretrol turns off the boiler a little before the end of the heat timer cycle. When it's warmer, say in the 40s, it usually turns off at 3 PSI or lower.



So we know we have to balance the system. Some people are cold, others hot... Several of the risers have been capped and don't have any vents. There are only a few vents on the mains and they seem small. So it seems clear what needs to be done from a venting perspective.



I'm also concerned because so many have removed their radiators over the years whenever anyone complained about cold, the super just turned it up (instead of looking at venting). There are many apartments that are heated solely from the risers. Could this also be a reason for the pressure to rise, that the steam isn't condensing fast enough because there are so few radiators? The boiler is essentially oversized to the system. This is my uneducated guess.



So I was thinking once we add vents and balance the system, we can turn down the heat and add radiators where needed... Again, an uneducated guess... a little knowledge from Dan's books can be dangerous!

Paul48

Methodical

Start with the main vents, and any riser vents.Post the size and length of the mains and someone will tell you how much venting you need.Get the pressure down to 2 lbs maximum.The lower you can get the pressure, the more money you save on fuel.Then deal with cold residents.There is no worse feeling than not being able to get warm in your own home.

Travis_F

more info...

THanks Dave, Nicholas, and SWEI. This is all very helpful. Here's some more info.. It's a single pipe steam with a power burner running on #2 oil. It's a single boiler. We are a coop in downtown NYC, 70 small units. I've also read about a vaporsat being able to switch the boiler to low flame once pressure is established. Was thinking that could also be beneficial to us as we work out the balancing / valve issues.

SWEI

you're on the right track

fix the venting and work on balance first.  Once you get the pressure down to where it should be (several variables come into play on that) you can take look at the control strategies.



Post some photos of the boiler and the near-boiler piping.  Get multiple angles and include any main vents.

sreja

re: Pressuretrols working with Heat Timers

Travis,.



I'm in a 14 unit condo, and can give you a few observations from our system, which uses a Tekmar controller (functions similarly to your Heat Timer).



Once you get your system working properly, the pressuretrols and the timers work hand in glove and ensure the system operates efficiently.



The job of the heat timer controller is to keep the boiler running an approximately reasonable portion of each hour based on outside temperature.  The pressuretrol is a much finer control, whose job it is to stop creating steam when the radiators are satisfied.



So if your problem is that your pressuretrol is hitting pressure prematurely, before steam actually gets to most of your radiators, then you may have to improve venting sot hat doesn't happen.



You spoke about an option to switch between low and high fire.  We have such a system on our boiler and I can confirm that it really does make a difference when trying to achieve pressure under 5psi -- allowing the boiler to switch between low and high keeps the pressure more regular than having to switch on and off.



The other thing I can highly recommend to you, though not cheap, is the use of TRVs on the radiators.  These made an enormous difference in our condo in terms of comfort level of residents and eliminating over and under heating.  Really cannot recommend them enough.

JohnNY

It's like this:

There is one pressuretrol that is a limiting control for the boiler and is wired directly into the burner's power circuit, in series with the Heat Timer's, or Tekmar's, "boiler" terminals. It is normally in the circuit-closed position and allows the burner to run on a call for heat until, on pressure rise (whatever you set it to), it opens the circuit and shuts the burner, even though there is still a call for heat. This is normal function during the "on" portion of the heating cycle.



If you've got a Heat Timer, you need something to tell it when steam has been established in the system. You can use a heat sensor on the end of the piping or you can use a pressuretrol at the source of steam, in this case the boiler.



The HT's pressuretrol works in the opposite way than the operating control. It is normally in the circuit-open position and, on pressure rise, it closes and sends a power signal to the circuitry in the HT/Tekmar telling it steam has been established in the system.



At that point the HT/Tekmar begins counting down it's determined rest-of-the-on cycle of the total on/off "weather calls for heat" or "heat demand" cycle.



Capeesh?



One pressuretrol works the burner, the other talks to the Heat Timer (or tekmar or whatever).

And since you're a multi-family, you've got another pressuretrol with a red reset switch that gets set up high and shuts everything down in case the other controls fail.



99.9% of the time, the pressuretols will oppose each other, one being closed and one being open. Only the limit control will turn the boiler off directly. The other one just talks to the master boiler controller.

nicholas bonham-carter

Control problems

Many people seeking help with steam problems here seem to have had a heat timer installed as a universal panacea for all system problems. The sales force for these devices were better than the technical departments.

In the case of using a pressuretrol as a "steam established" sensor, I can see a problem: an air-bound system would still have a back-pressure of 2psi, and yet steam has not really been established. A better solution would be a thermal sensor at the top of the riser.

Since your system has an obvious potential for great fuel savings, why not get a real pro in who understands the heattimer smoke and mirror principles, such as John whose explanation of these complicated devices shows such understanding.

With your system, you will want to start saving money on fuel, and raise comfort levels right away, before the winter is over. Don't allow anyone to think that if they are cold and fuel cost is X, then to be warm the fuel cost will rise to 2X, as it will not. You are probably wasting fuel squeeeezing the air out of inadequate vents.

A good steam pro will be able to show those in charge of building services how to do various items of maintenance. He will also make sure the burner Is tuned properly (when was that done last?).

Keep us in the loop, so all here may benefit from your experiences.--NBC

nicholas bonham-carter

Missing radiators

How many radiators have been removed, and have they been stored, or thrown out?

It may be a bit late, but I would think that the residents must have been in violation of the coop rules to do so.--NBC

JohnNY

Thanks for the vote of confidence, NBC.

I agree with you 100% that installing an expensive boiler controller is sold as the cure-all for all kinds of problems that will only ever be solved by proper piping, venting, sizing, tuning, etc.



It's a complicated world out there.