Increasing the Energy Efficiency of Old Boilers
O&M and upgrade tactics can provide savings when purchasing a new unit is not an option.
When I was young, I used to love watching magicians and was amazed how they would pull something out of what appeared to be an empty hat. That seems to be the kind of clients that I have attracted in my career. They all want the state-of-the-art heating system with no money in the budget for the system. I would imagine that you are seeing the same thing. This has forced me to be creative to help the clients to increase comfort, lower the utility costs all with a limited budget.
Do they want to save money?
Many clients say that they want to save money but few are able to invest in the technology required to get a more efficient heating system. Perhaps it is due to the price of natural gas that is so low that precludes people from updating their equipment. I think that they want to do the right thing but capitol expenses only seem to be approved when the equipment is dead. It seems like the administration of commercial buildings think that HVAC systems last forever. We are seeing many even try to repair equipment that should have been replaced years ago. My favorite line is “We just need to get through the winter and then we can look at a new boiler.”
Is it worthwhile?
Energy savings is a consideration when replacing the piece of equipment. For instance, will the client save enough in utility costs to pay for the replacement cost when they replace an 80% efficient boiler with another 80% efficient boiler? I think not.
Another aspect in the decision is whether to replace it with a more efficient boiler that only lasts half as long as the traditional boiler? Will the utility cost savings pay for two boiler replacements in the life span of a standard boiler? Consider this: The Chartered Institute of Building Services Engineers, based in the UK, estimate a life expectancy of about 15 years for a standard condensing boiler. Standard 80% efficient boilers have a life span of about 25 to 30 years. Will the client save enough with the condensing boilers to cover the cost of the additional boiler replacement?
In addition, the high efficiency boilers will require more maintenance and what about the environmental impact of the scrap boiler? I was giving a speech for the colleges and universities in my home state and the director of maintenance for a major university told me that his 20-year-old boilers were still running great and he was replacing the 10 year-old high-efficiency boilers. This should be explained to the owner and factored into their decision.
Who will do the maintenance?
This is one of the most overlooked factors when designing a system. I went to a nonprofit facility that asked for help with their fuel costs. The heating plant consisted of newer high-efficiency boilers and variable speed pumps. The boilers and pumps were running on manual override because the owner could not afford the service agreement cost for the newer equipment so they did what they knew, they bypassed the operating controls and had the equipment running on the limits. I explained that they would most likely pay for the service calls out of the utility budget but they did not have money in the budget for maintenance. They received a grant for the new boiler but had nothing for maintenance. Perhaps, we should include a five- to seven-year service agreement in the initial heating system replacement scope.
Perform planned maintenance
If the client cannot afford a new system, the first thing I do is make sure that the current equipment is working the way it was designed. This includes regular maintenance of the equipment. This service call will check all wiring connections and verify the proper operation of the safety and operating controls.
The least expensive and most cost effective service that you can provide for a client is to check and adjust the fuel to air ratio of the burner. The fuel savings could easily eclipse the cost of the service call. In addition, it could make it safer to operate.
Turn it off
A simple but often overlooked way to save energy is to shut off the energy consuming device. If the heat is not required, perhaps the unit could be shut off.
Turn it down
Another easy way to reduce operating costs is to reduce the steam pressure or water temperature. Be careful when reducing the water temperature on a standard boiler as it could cause the flue gases to condense if the boiler water temperature is below 140ºF. When lowering the steam pressure on industrial or high pressure applications, check the ratings of the equipment such as sterilizers, steam heat exchangers, or pressure reducing devices. Their ratings may limit how far you could reduce the steam pressure. Even if you cannot reduce the steam pressure or water temperature during the day, perhaps you could do so at night. A hospital in my area was able to reduce their boiler steam pressure when the laundry in their facility stopped working in the afternoon.
Loosen the control parameters
Many of the control companies pride themselves on the accuracy of their control systems when in reality that may be increasing the operating costs. When the client has tight control parameters, this could cause short cycling of the equipment. If you can allow a larger drop in temperature or pressure, the boiler burner will operate longer, increasing system efficiency.
Isolate the boilers
This could be either isolation valves or primary secondary piping. Isolation of the idle boilers can result in reductions of 2-5%. If using isolation valves, care has to be taken so that the boilers will not trip the manual reset temperature or pressure limit.
When adjusting the fuel to air ratio of power burners, it involves the setting and adjustment of linkages on the gas valve and air damper. There are several manufacturers that produce linkage-less systems. According to Honeywell, this could save about 5% on the fuel costs. This also assures the correct fuel to air ratio throughout the firing range of the burner.
Variable speed blower motor
On large industrial boilers, this may be cost effective when the burner is not always firing at high fire.
Did you know that an average steam trap will open and close over 160,000 times in a typical heating season? That was according to an article entitled “Maintaining Steam Traps” by Daniel Kaplan in The Cooperator Magazine. Many buildings have old, inefficient steam traps which should be replaced. According to www.SchoolFacilities.com, the average life of a steam trap is three to six years.
Increase pump efficiency
On traditional hydronic systems, the circulating pumps may operate for several thousand hours per year. A way to reduce the pump operating costs is to replace the old pump motor with a newer more efficient motor or even install a variable speed drive on the motor. In some instances, it may be a better solution to replace the entire pump with a new more efficient one. According to ASHRAE, base mounted pumps have a median life of 20 years and pipe mounted pumps have an estimated life of 10 years.
Oxygen trim systems
These systems are becoming more cost effective. These were traditionally used on larger industrial boilers. The oxygen or O2 trim systems use an oxygen sensor in the boiler stack to monitor the oxygen content of the flue gases. The sensor will then instruct the control to adjust the fuel to air ratio of the burner to always be at the most efficient setting.
These are twisted pieces of metal that are installed in the tubes of a fire tube boiler to increase the turbulence and the heat transfer ability of the tube, resulting in lower heating costs.
ASHRAE lists the median life of a boiler between 24 to 30 years while a burner has a life expectancy of 21 years. The burner manufacturers suggest that a new burner can substantially reduce operating costs. Many designers or installers are hesitant to replace just a burner as they feel that they will have to assume responsibility for the entire system, including the old boiler, but this could be explained to the client. The replacement burner may also be able to be transferred to the new boiler as well, lowering the installation costs.
Fire door burner
A variation of the replacement burner in the base of the old horizontal fire tube boiler is to install one in the boiler fire door. The replacement burner will typically be smaller than the old burner. The boiler maintenance costs are lower as well as the refractory base which has an estimated 10-year life. The burner manufacturer will give you guidance on how to do this. Power Flame suggests partially filling the base with aggregate, millboard, and calcined aggregate. Typical savings are about 7-15%.
Front End Loading
When I first heard this term, I thought it was some sort of cosmetic plastic surgery. After it was explained to me, it seemed like a perfectly capable idea. In this scenario, we leave one or both of the existing boilers in place. We install a small efficient boiler that will handle the shoulder times of the year. The new boiler will be about one fourth of the boiler size required. It may handle the heating load of the building down to 32-40 degree outdoor temperature. If one of the existing boilers is in disrepair, we may remove the defective boiler and “part” it out to keep the remaining boiler operational. The new boilers may be condensing or even wall mounted, and are directly vented through the side wall.
If the system has reheat coils, a summer boiler may be the perfect answer for this facility. This small efficient boiler could be used to supply hot water in the summer to the hydronic reheat coils.
Flue gas heat exchanger
A way to really slash the operating costs for an older boiler is to install a flue gas heat exchanger. According to HeatSponge.com, savings of 3-17% are common by installing a heat recovery unit. The unit will pull the excess heat from the flue gas and use it for heating the boiler feed water or other processes. Since these recover the latent heat in the flue gases, the outlet may not be able to be vented into the existing chimney.
Replace the boiler
In some instances, a replacement boiler may be the only solution. If the old boiler is leaking or in disrepair, the client may be forced to look at a replacement.
Dale Carnegie, the famous sales trainer, once pondered why almost a million 1/4-in drill bits were sold yearly. He correctly theorized that the people did not want drill bits but rather wanted 1/4-in holes. What does this have to do with boilers? Most people do not care how their boiler works. They simply want heat in the building when it is cold outside. In other words, they do not want calls from cold tenants or employees. I believe that once they are assured that they will have heat on those cold days, you may be able to discuss the financial implications of their decision. Let us consider two different boiler options for the customer. One will cost about $5,000 more than the other but will save about $2,500 per year.
That shows a two-year payback for the client and many building owners would opt for the higher efficient system. If the client decides on the less expensive boiler and will invest that $5,000 into an interest bearing savings account that earns 2% interest compounded monthly, they would earn $2,456.64 after 20 years. That return would be almost 50% after 20 years. The client may be patting him or herself on the shoulder for such a prudent investment but that is not the entire story.
Now, let us consider the more expensive option. The client invests $5,000 into the more efficient system that will save $2,500 per year. Assuming that he or she will invest that savings into an account with a 2% annual interest rate, compounded monthly, over 20 years, the $2,500 would be worth $41,116.20 or about 820% return. There is also a rule of thumb in commercial real estate that says that a building value is about 10 times the annual net profit. If we are able to reduce the building costs by $2,500, the building value just increased by $25,000. This more efficient option will return $61,116 to the owner after 20 years. I like that better than the $2,456.64 and so will the owner. This does not factor in any fuel cost escalations.
When I do my seminars, some of the attendees would say that customers would always choose the more expensive option. They argue that a two-year payback would motivate the customer to buy the more efficient system. I have not found that to be the case but for conversation sake, let us assume that our new system would only save $1,000 per year, extending the payback to five years. Would it still be worthwhile? If the client invested that $1,000 savings into an account bearing 2% interest, the customer would get $24,508.92 after 20 years. The $1,000 energy reduction would make the building worth an additional $10,000. This would equal $34,508.92. It still beats $2,456.64 by a factor of almost 10. It pays to educate the client on the financial implications of the choices.