Choosing a Boiler/Hot Water Heater for your Hotel

The following advice is a simple generalization with rounded numbers.

Use the examples at the end to figure your needs based upon your need and fuel costs.

 

 

Price of Equipment vs. the Price of a Customer

This is a management issue. If customer satisfaction and repeat business are not a top priority in your business, read no further. Buy the least expensive item you can find. If repeat customers are important to you, read on.

Understand that the price of metals and construction constantly rise and that a purchase of equipment that is designed to last 10 or 20 years or more is a better investment than replacing with something similar that might last only 5 years.

The reality is that people usually use hotels for comfort and relaxation. Heat and hot water are a foundation of human comfort. That justifies a major investment in heating equipment. Water heaters in sizes needed for 50 room hotels range from -U.S. $12,000 to over $50,000 and boilers are about 50% more.

 

 

Know a Btu

A Btu is a British thermal unit

1 pound of water raised 1 degree f (Fahrenheit) = 1 Btu

A gallon of water weighs 3.78 kilograms (lbs.) or 3.78 kilos

1 liter weighs 2.25 pounds so 1 liter requires 2.25 btu´s to raise 1 degree f.

 

Values of fuels @ 100% efficiency

Electric   1 watt        =     3.5 Btu´s                       (1kw = 3,500 Btu´s)

Petrol      1 gallon = 120,000 Btu´s                     (1 liter = 31,746 Btu´s)

GLP         1 gallon =   96,000 Btu´s    (                1 liter = 25,400 Btu´s)

Coal         1 kilo         =   28,000 Btu´s

Wood      1 kilo         = 10-12,000 Btu´s

Note that Btu ratings on equipment are usually in Btu´s/ hour.

 

How much do I need?

A typical 4 meter x 8 meter room in a cold climate uses about 5,000 btu´s continuous heat and 10,000 btu´s on warm (1 hour) up of air. Always factor in 10% more than total needs to allow for problems or expansion.

An average customer uses about 20 gallons of hot water in a morning shower.

If there is a restaurant, allow another 5,000 btu´s per customer for cooking if steam is to be used (marmitas, hornos)

Hot Water and Hot Air

Heating water is a simple straightforward calculation and storage can be factored in. Air is much different. The size of a room has to take into account the amount of mass in it and also moisture in the air. A big difference in heating cost is found when insulating and weatherproofing is used.  Finally, the type of customer makes a difference. Older people need more heat and children are notorious for leaving doors and windows open. While only 5,000 btu´s may be needed on an hourly basis, that amount could be doubled with active children.

In a hotel with only internal access and multi levels, needs are greatly reduced while stand alone rooms have much higher energy needs.

 

Why Steam or Hot Water or Both?

 

· Steam is a clean and very rapid way to transfer heat and is non-flammable or electrical. Steam equipment typically is very long lasting.

· Hot water is a safe and non-drying way to warm air. Also, direct use of hot water is often used in smaller applications such as shower or laundry.

· Steam will allow for rapid recovery while hot water is generally stored in a tank if flow is intermittent but heavy        (such as laundry).

· If space is an issue, then steam is a good choice.

· If a large volume of water in an intermittent load which also has a long recovery time available (laundry) is needed a tank with heater is a more economical choice but note that tank heater could also be steam. Note again, that if this tank has a single application, again such as laundry in a hotel that does not use much heat elsewhere, then direct heating of the tank is the most practical choice. The use of tanks or volume of water in a boiler is often referred to as ´battery effect´.

 

Commercial duty tanks allow for cleanout of accumulated minerals that destroy domestic tanks. Annual maintenance of these tanks gives a working lifespan of up to 20 years.

Boilers, for safety reasons, are always built extra heavy. Note that there are times that hot water heaters are called boilers but observe closely their specifications do determine if they are steam or hot water. Generally, steam that leaves the boiler to do its work returns back to the boiler as condensate or water. The use of clean, distilled water over and over again means that no minerals accumulate and if the water is treated with a small amount of chemicals to maintain pH, a boiler can live longer than a human.

Water heated by steam in a heat exchanger does not accumulate minerals too fast so maintenance of steam powered units is minimal.

 

Battery Effect

Water has the ability to absorb, store and release heat quite efficiently. Thus, by storing hot water in a tank, we can have hot water on demand and use as much as we want, up to the limit of the size of the tank. In a boiler, more heat energy can be stored in the water and the water when converted to steam can release the heat very quickly (see example). This translates to more heat stored and converted in a smaller space.

If space is an issue, a boiler may be the best choice. Note that a key component of a steam system is the heat exchanger which transfers the heat in the steam to heat water or air. Although expensive, heat exchangers last 50 or more years and if used within sight, can be made very beautiful.

In short, steam can deliver large amounts of heat quickly and efficiently over long distances while hot water in a tank is more economical if directly heated and kept close to the use which is a limited and preferably single use.

One big factor that cannot be overlooked is that some boilers that are economical to purchase have very little storage capacity. Cast iron boiler systems hold very little water and use the mass of the iron as a battery. As such, they cannot handle surge loads. The amount of fire needed to size a cast iron boiler to match the full use of a hotel is many times greater than in a boiler with a high volume of water.

 

Demand and Steady Loads

Irregardless of the type of system, hotels have 2 different types of loads-Steady and On-Demand.

Knowing the amount of heat and hot water necessary is strictly a management issue. Questions such as ´how many gallons the morning laundry uses´ or if the kitchen is steam powered or even use of hot tubs/saunas must be determined and translate to cost per customer (see example).

A room could be calculated at a continuous use of 5,000 Btu´s per hour continuous but a surge or warm up time must be figured into calculations. A 15 minute shower can consume 20 gallons of hot water and can be considered a steady load of 2,000 Btu´s if a tank is used or a surge load of 16,000 Btu´s if heat exchangers are used. Kitchen use of steam can surge several hundred thousand Btu´s and a hot tub may need 100,000 or more Btu´s per hour if it is to warm up in a reasonable amount of time but only 1 or 2 thousand Btu´s per hour to be kept warm.

Laundry is its own animal and investments in efficient machinery can reduce hot water costs by factors of 5x or even 10x.

 

Efficiency is Relevant to Cost (it’s the little things that add up)

Generally, investing on the use end saves double or as much as 10x energy needs and the difference in efficiencies of boilers can vary by 10% or more. Quality of construction usually translates to more investment. The use of automatic controls adds to the initial cost but saves energy. Also, equipment used in steam such as marmitas, radiators and heat exchangers have a high initial cost but a very long lifespan.

Steam is always a bigger capital investment but pays for itself many times over in customer satisfaction, efficiency and lifespan.

With direct-use water heaters, allowance for cleaning and maintenance add to initial cost but keep the unit operating at peak efficiency.

 

Type of fuel determines the cost of construction

This fact is seldom understood. It is the fire end and not the water end of units that determine how it is built; electric being the cheapest and wood being the most expensive.

It is a question of metal and size. With electric, simple elements can be inserted into the tank. Cheap and reliable and easy to control and maintain, there is little involved in construction of a heat unit.

Next in line is gas. Burners are clean, have no moving parts in smaller sizes and are easy to control and maintain. The addition of tubes of one sort or another adds considerably to construction costs but generally, controls and extra material are kept to a minimum.

Then comes liquid fuels such as petroleum. These require mechanical burners to provide air and fuel in the right mixture and the more efficient the design, the more expensive the burner. The corrosive effects of fuels require that the design be a little more robust than gas. Thus, more expense is incurred.

Solid fuels such as coal and wood require the most robust construction, take up quite a bit more space and must be designed for high amounts of serviceability. While raw material may be economical, there is more labor involved and abuse of parts. It also takes more space and time to burn than a refined fuel.

…On the other hand, nothing beats the sex-appeal of watching a raw fuel being converted to useful work. A wood-fired boiler always draws a crowd and if attached to a steam motor, it becomes the subject of post cards and promotional campaigns.

 

Leasing and Warrantees

While many hotels are nothing more than family operations deflating an inheritance, most hotels are professionally run for profit. Such hotels live by the motto ¨The answer is Yes! What is your question?¨  Quality hotels should demand their equipment be manufactured and supported with the same philosophy.

 

Imports seldom can provide a warrantee that ensures rapid resolving of a problem. It is best to keep things local and boiler makers have a natural pride in their workmanship and engineering. Warrantees from local builders are common and an even better insurance of reliability can be had if there is a leasing program. With the entire operation of a hotel relying upon heat, a warrantee of operation should be the deciding factor in your capital investment.

 

Serviceability- The difference between commercial and domestic duty

Even the best of warrantees do not guarantee successful operation 100% of the time. Boiler and water heaters engineered for commercial duty are designed to be repaired with simple tools and readily available parts. More importantly, they are designed to exist under extreme conditions and be periodically maintained by professional maintenance men.

Domestic units on the other hand are designed to have a limited life and be disposed of when wear and tear takes their toll in but a few years. Lack of maintainability allows for cheap construction and if repair is required, it is usually done by non-staff members which are always expensive.

If a water heater with direct use of fuel is being used, facility for repair and cleaning add greatly to the initial cost, but give a lifespan of 20 years or more.

 

Example:            Arequipa hotel with incoming water at 40°f heated to 140°f for shower.

Heat 1000 liters(264 gallons) 100°f. (37.78 C)

264 x 8.34 x 100 =  220,176 Btu´s

Petrol @ US$6.00 gallon… 6 x 220,176 / 120,000 = $11.00

Efficiency of heater 80% so 11 / .80 = $13.76

 

Example:            50 room hotel in Arequipa with restaurant (needs and size of unit)

    Heating rooms                  5,000 Btu´s continuous & 10,000 Btu´s 1 hour surge x 50

    Shower hot water             1,000 Btu´s cont. or 30,000 surge, x 50 over 2 hours

    Heat office                      20,000 Btu´s cont.

    Heat restaurant                30,000 Btu´s cont.

    Cocina                             20,000 Btu´s cont. & 500,000 1 hour surge

    Laundry (w/tank)            20,000 Btu´s cont. & 100,000 1 hour surge

 

Cont. (50 x 5,000) + (50 x 1,000) + 20,000 + 30,000 + 20,000 + 20,000 = 390,000 Btu´s + (losses & efficiency)

Surge = (50 x 10,000) + (50 x 15,000) + 500,000 +100,000 = 1,850,000 Btu´s + (losses & efficiency)

 

Example:            Energy cost 2 customers, 24 hour stay no pool or hot tub.

 

Laundry   10 gal. hot water             = 10 x 8.34 x 100 = 8,340 Btu´s

Cocina     5,000                               = 10,000 Btu´s cooking

Shower     20 gal. x 2                       = 40 gal. = 40x8.34x100 = 33,400 Btu´s

Room heat w/ 1hr. warmup            = 5,000 x 20 hours + 5,000 more for 1 hour = 105,000 Btu´s

Heating restaurant/office                =50,000 Btu´s / 100 customers x 2 (x 20 hours) = 20,000 Btu´s

 

Total: 8,340 + 10,000 + 33,400 + 105,000 + 20,000 = 176,740 Btu´s

Divided by $.10 kW electric = $5.05      Divided by $6 gal. Petrol = $8.84

This does not take into account factors such as amortization and liability.

 

Example:            Surge capacity

With water tanks, figure recovery time based upon heat supplied.

50,000 Btu burner = ?# Gallons 100ºf in 10 min. = (1/6(.166) x 50,000)/100/8.34 = 9.95 gal. (38L)

 

With steam boilers, each gallon of water at 15 psi holds about 315 Btu´s available for instant release of heat. A boiler with a 1 million Btu burner needs 150 gallons extra capacity to give a 300,000 Btu extra surge (15 min.). That’s 10 showers running at once.

Boilers are often rated in Btu´s or horsepower based upon maximum flame potential. This is a separate rating from their surge capacity. Such boilers have to be sized to the maximum demand of the hotel.

Horizontal fire tube boilers hold the most water while water tube boilers give the most power in a given space. Cast iron boilers are gentle and long lasting, but do not hold much storage.

Generally, a hybrid system consisting of point of use and storage tanks are used in hotels which give good surge capacity with smaller boilers and thus, lower costs but high efficiency. Management must determine where steady and high demand locations will be in a hotel.

 

 

 

 

 

Work Sheet

 

A. Gallons required          ______

B. Weight (x8.34lbs)         ______

C. Temperature rise          ______

 

Btu´s required: A x B x C = _____ x 8.34 x ____ = ______

 

Btu Hourly & Daily use: (32 square meters 5,000 Btu´s per hour average)

Room needs (constant and surge) x number of rooms

Hourly: ______x_____ = _____   & surge:  ____x____ = ____

 

Shower use: number of guests x # gallons x 8.34 x 100ºf

______x ____ x 8.34 x 100 = _____

 

Cost per Btu: Fuel Btu content / Fuel cost

           Electric      (3500btus-kw)          3500/  $_____ = $_____ per ___ Btu´s

           GLP      (95,000 Btu´s/gal.)      95000/   $_____ = $_____ per ___ Btu´s

           Petrol  (120,000 Btu´s/gal.)   120000/   $_____ = $_____ per ___ Btu´s

           Coal      (28,000 Btu´s/kilo)      28000/   $_____ = $_____ per ___ Btu´s

           Wood    (12,000 Btu´s/kilo)      12000/   $_____ = $_____ per ___ Btu´s

 

(1) One boiler horsepower = 34.7 pounds of water converted to steam or rounded up for efficiency is 35,000 Btu´s. Heat required is 35,000 / efficiency in %.

A 25 horsepower boiler requires (?) @ 85%. = 25 x 35,000 / .85 = 1,030,000 Btu burner (approx.)

 

 

 

Cost per Btu

Example = Amount / #btu´s.

 Petrol, $6 gallon =

 120,000/600 = 200 Btu´s per $.01

 Electric: $.10 kW =

 3500 / 10 = 350 Btu´s per $.01

                 $.07 kW =

 3500 / 7   = 500 Btu´s per $.01