In our long experience in the field of HVAC (heating, ventilation and air-conditioning), we have found that controlling humidity has been until now one of the aspects of air conditioning that has been somewhat neglected. In our everyday experience we find many units switched off or out of order because either they cause the owner or maintenance technician a lot of problems or because due to their location in the installation they undergo significant deterioration in very short period of time. Our impression is that this component of the HVAC installation is often regarded as superfluous because, in general, there is little awareness of the negative effects of an environment with a very high or very low range of humidity, frequented by people. This article sets out to convince those responsible for the design, installation and maintenance of these installations of the importance for both people and buildings of keeping air vapour content under control. In this way we can swiftly relate this lack of control of humidity to a number of problems in buildings that we often encounter, namely:

1.- Comfort

Our perspiration evaporates to regulate our body temperature and dissipate internal heat. The low relative humidity typical of many interior environments in winter leads to an average temperature of 21-23ºC, perspiration evaporates and we feel colder than we really should at that temperature.

Conversely, in summer we find rooms that keep the air above the recommended maximum level of humidity for comfort, 50-70% R.H. (relative humidity) due to a lack or fault of humidity control and the body is unable to evaporate the perspiration we generate to dissipate our body heat.

In a study[1] conducted at comfort temperatures of 21.1 and 27ºC and with dew points between 2.2 and 20ºC, of 20 people engaging in sedentary activities and dressed in light clothing, it was shown that the psychological response to thermal comfort (not acting to adjust it by, for example, opening the window, removing clothing, etc.) 90% of the individuals felt better when the R.H. was in the region of 50%. This is reflected in figure 1, where the TAC (Thermal Acceptance for Comfort) is supported, at comfort temperatures, by the largest number of individuals for a R.H. of around 50%.

[1] Berglund, L. G. y W. S. Cain. 1989. “Perceived air quality and the thermal environment.” The Human Equation: Health and Comfort. Proceedings of ASHRAE/SOEH Conference IAQ ’89 Atlanta: ASHRAE, pp. 93-99.

2.- Health

Dryness of the skin directly affects several metabolic functions, including oxygen intake, the shedding of water vapour, salts, heat, etc. Excessive evaporation of this water vapour means that its replacement via capillary diffusion is insufficient and problems arise related to the dryness of the skin, whose effects we have only recently become aware of.

It is also useful to know that several studies have shown that at very low or very high levels of humidity, micro-organisms find environments that are more favourable for their survival. This happens for three reasons:

• At high humidity, moulds thrive and to survive they emit spores (the typical “damp smell”) to prevent others from growing. These spores undermine the operation of our immune system.
• As humidity increases, the amount of dust present in the atmosphere diminishes, both in terms of its production and its maintenance in suspension, as the humidity encourages deposition due to gravity. The amount of dust present in an environment impacts directly on our health, as the micro-organisms travel by adhering to these solid particles.
• Finally, at low humidity, the mucous membranes that prevent harmful bodies from getting inside our body do not perform their protective role.

This interaction of the human body is revealed in several studies which have shown that there is a relationship between the humidity level in an enclosed space and the proliferation of mites[1]. The droppings of these mites and insects are a rich source of food for moulds that thrive among persons with respiratory illnesses, such as rhinitis or asthma. The same studies have revealed that children and adolescents are more prone to these illnesses.

Around 50% of an insect’s body is composed of water. If it loses this water, the insect is less active and has a lower reproduction rate. Moderate temperatures with high humidity are the ideal medium for it to grow.

By reducing the humidity in buildings, we can limit the proliferation of mites and insects.

In figure 2, we can see how, as the height of the home above sea level increases, the number of asthma patients suffering from positive reactions to dust in the home decreases. For the same air condition, the air humidity decreases as the height above sea level increases.

3.- Static electricity and IT equipment failure

Air with a relative humidity of under 45% permits electro-static charges to accumulate in many types of IT equipment and even in people. Static electricity originates in our environment continuously due to the friction of materials with high electrical resistance against one another. A typical example is when people walk on carpet. This electricity is only a problem when the ambient conditions allow it to accumulate, which not only causes unpleasant effects such as when a person receives a discharge, but also when there is an explosive or inflammable atmosphere, with the risk that this represents.

In addition, these phenomena are very important in computer rooms and data processing centres, where they can cause problems such as electronic faults in circuits, dust accumulations on reader heads and even breakage of stored magnetic media.

Increasing R.H. does not prevent the forming of these charges, but it does prevent their accumulation.  Suitable increases in R.H. produces a fine layer of humidity on the surfaces of the materials that allows the charges to travel to earth before they reach high levels of potential.

Figure 3 shows the measurement of electro-static discharges produced in a workplace with carpeting according to the relative humidity of the environment.

4.- Enhanced efficiency

Many times we find that the consumption of the terminal units in temperature control rooms, such as a split, is very high. This is generally accompanied by a significant evacuation of condensates.

If a more exhaustive analysis is conducted of this situation, it may be concluded that the energy consumption is used not only to cool the air, but also to dehumidify it.

The dehumidifying, in this particular case, is an energy loss, or to put it another way, a financial loss, which can be avoided if the humidity in the primary air feed is regulated. This can be done, for example, with an enthalpic recuperator that reduces the humidity load. Approximately 80% of latent heat loads come from outside air.

In this way, the heating units will be used specifically for sensitive control, reducing their energy consumption.

A sustainable focus on machines used for buildings is very important as according to date from the European Union and US Goverment, we consume 40% of the energy we produce in them. HVAC machines and their auxiliary elements have to become increasingly compatible with renewable energy sources and the maximum efficiency of energy use.

5.- Deterioration of materials in buildings

Corrosion

A host of metal elements are to be found in buildings and these will be more or less important depending on what they are used for. This use can vary from a structural element to an ornamental function. Examples of typical failures in materials caused by this kind of degrading are the loss of mechanical properties, warping, pitting, joint failures, etc. This entails the replacement of the element in questions and the cost that this represents.

A metal corrodes when an electrical current flows from an area with more potential to one with less. This phenomenon is accelerated when there is an electrolyte present, such as a fine film of water.

This film of water is formed, in broad terms, due to the condensation of the relative humidity present in the air around a metal surface. This is either through the impact of the air particles on the metal or because there is a thermal bridge because this surface is at a temperature that is lower than the ambient temperature. In both cases, the condensate increases as the air’s R.H. increases.

According to studies by J.C. Hudson, there is a critical R.H. for each metal from which the rate of corrosion increases exponentially.

Humidity in partition walls and ceilings

In humid climates, it may happen that negative pressure is generated due to air extractions. This would lead to air filtering into the building, collecting in cavities between partition walls and ceilings. If there is an area where the temperature is lower than that of the infiltrated air such as behind a curtain or a sofa, this may cause saturation and even condensation. This would provide sufficient humidity for the growth of mould, showing up as what are popularly known as “rising damp”.

Humidity in bookshops

Something similar occurs in bookshops. However, here there is a further problem: they retain humidity. Thus, it is not just a question of a type of humid or damp climate, but of humid/damp months throughout the year. Every time the relative humidity rises by approximately 50%, the books will absorb humidity without releasing it. This becomes more serious still in book depositories and warehouses.

For this, a possible solution is to install a dehumidifier that maintains the R.H. below that figure at all times, regardless of the temperature.

6.- Conclusion

As we have already mentioned in the preceding paragraphs, humidity control is important not only from the point of view of material conservation but also in terms of human health.

By material conservation we mean preserving the properties and characteristics of the elements that form part of the building, on a permanent or temporary basis. The issue that is most worrying in this regard is corrosion. For this reason, rigorous control of relative humidity can help to prevent losses of materials, with the resulting financial loss.

More important still are the aspects related to human health, such as the proliferation of fungi, insects, viruses, and bacteria. We have already commented briefly on how the ambient conditions can affect their development, one of the chief factors being relative humidity. The consequence of ignoring such factors can lead to respiratory illnesses, which in principle are avoidable, such as allergies, asthma or rhinitis.

In the following figure, and in summary form, one can see the intervals of relative humidity in which the various organisms studied co-habit.

To sum up then, the limits set by different building codes in terms of relative humidity are neither capricious nor arbitrary – they seek to prevent the problems we have described.

Other added benefits stem from humidity control, such as an energy saving in the air conditioning of rooms, preventing the accumulation of static charges that can be generated by the friction of materials, and contributing to higher performance of IT equipment.

Fortunately, the trend in recent years has been to return to prevailing concept of the importance of controlling R.H. and so this is increasingly viewed as being of equal importance to controlling temperature.

8.- Bibliography

• ”Humidity control design guide for commercial and institutional buildings”. Harriman, L., Brundrett, G., Kittler, R., Ed. ASHRAE, 2006.
• “Montajes e Instalaciones. La importancia de la humedad relativa en la calidad ambiental”. Rodriguez Ramos, P. Ed. Separata, Septiembre 1992.
• “Humidification Handbook”. Morton, B. W. Ed. DriSteem, 1998.

For some time now, the expression “clean steam” has drawn the attention of technicians who have been using steam for a range of different purposes in the pharmaceutical industry.  The terms is used to refer to it as a heat-conveying fluid or a source to provide specific humidity to the dry air flows in HVAC systems in pharmaceutical installations.  The purpose of this article is to relate the importance of the steam’s quality for HVAC installations, the current regulations and the generating systems that are now at the cutting edge of air humidity control equipment design.

Boiler Water

HVAC technology is in many cases derived from technology applied to industrial processes. The feeding of water vapour, using air humidifiers to achieve a controlled relative humidity level in the human-occupied environment, began to increase in popularity in the early 1970s. This humidity control became increasingly important in Spain until the national regulation, issued by the Regulations on Heating Installations in Buildings of 1997, made the control of relative humidity in all public buildings mandatory.  During the early years of air humidity control, the first configuration of the air humidifier was the one shown in figure 1.  Systems to feed water vapour to dry air were firstly designed as a complement to centralized networks of boiler water designed for heating or industrial processes by means of humidifiers that treated part of that pressurised steam in order to be able to inject it into the primary air ducts in winter.. This kind of equipment has been in use for over forty years with very good precision, high durability and virtually zero maintenance.

These systems whose functional model is shown in figure 1 consist of a reducing valve to move the boiler steam at an adjustable pressure in HVAC systems (from 1 to 15 bars), a small Y-shaped filter to filter the steam from the network (1), one or more steam lances with a heating jacket (1) through which the pressurised steam flows to prevent condensation of the steam that we inject, a steam separator (2) which separates the liquid from the dry steam (3) by the centrifugal force that produces the spinning of the steam using a baffle, a steam intake in the centre of the separator, a control valve(4) that modulates the steam injection according to demand and restores the steam to almost atmospheric pressure. Finally, we have the steam lance or lances (depending on the load of the steam to the HVAC unit and the desired/calculated absorption distance) that injects the steam into the dry air via thermoplastic nozzles (5) calibrated to prevent condensation and noise. The steam is separated from the condensate (6) by means of a purger.

 

 Sanitation quality steam/clean steam

Between the end of the last century and the beginning of this one, a number of health and hygiene studies found that the volatile organic compounds that penetrated iron piping for boiler steam to prevent them from corroding were harmful for human health. These studies determined that the amines used to protect the piping networks had a toxic effect on the health of users in buildings who breathed in the humidified air in the workplaces where this type of humidifier was in use.

There has been a change in the law since the problem was discovered. All boiler steam networks that are used for air humidifying must use sanitary quality steam (Spanish regulation RITE 2007 IT  1.1.4.3.3), that is to say, steam that comes from water of sanitary quality which is clearly regulated by Royal Decree 140/2003 which enacted the water quality for human consumption sanitary criteria. Of course, this excludes toxic compounds that protect the networks from corrosion. To prevent its contamination by rust as well as to prolong as much as possible the life of the installation, there is a choice between two systems to produce and distribute sanitary quality steam:

 

1. A clean steam pressurized generator:

Clean steam free of chemical compounds is used in the pharmaceutical industry to prevent contact with this steam or its condensate from causing any contamination. The production of pressurized clean steam involves the use of specific generators with all of the components of the steam and condensate network (cut-off valves, regulation, reducers, filters, purgers, etc.) made of stainless steel of the highest quality. Clean steam of this quality, when it is pressurized, can easily cause piping network corrosion if they are not made of the highest quality materials and in addition, the steam itself may easily become contaminated if resistant materials are not used. When the steam is also used for air humidification all of the components of the humidifier must be made of the highest quality stainless steel. These systems are usually based on a boiler steam network and then a secondary boiler is added in the zone required that carries out the exchange with additive-free water to produce clean pressurized steam and distribute it through the required zones, injecting it in the ducts or HVAC units in the manner described above for the humidifiers using boiler steam injection but taking care that all of the components are made of the highest quality stainless steel. Depending on the use we make of the steam (if it is solely for use inside the HVAC installations or if it is also used for production processes, sterilizations or other applications in the pharmaceutical plant), sanitary grade steam can tolerate a water supply with an additional demineralization treatment by reverse osmosis, as required, in order to have water that is more or less clean. As we can see, the better the water quality, the higher the costs of producing, distributing and injecting it. In the diagram we can see the secondary boiler and the network of pressurized clean steam.

1. Production of saturated dry clean steam and distribution without condensates:

If what is really important is the air conditioning of the air in the pharmaceutical plant, another option which is increasingly adopted by many large  laboratories and hospitals, given the costs involved in the previous system, is to incorporate humidifiers that exchange boiler steam (which is unclean, with additives, in an economical closed circuit network) with sanitary grade or de-mineralized water if so required by the enclosed space or the precision of the system. This kind of equipment produces dry saturated steam under a level of pressure that is higher than that of the duct but very close to atmospheric and it is then conveyed to the ducts or HVAC units by steam distribution systems with virtually zero condensation. These systems produce steam by heating water and are able to handle everything related to the treatment of the water in their tank, controlling the use of boiler water according to the demand for humidification and also producing the right steam for the dry air flow to match it to a good dispersion of stream in the system.

Designing a good conduction of steam from the humidifier is essential in order to ensure that there are no major losses due to condensation.  The location of the unit must be given careful consideration so that the conduction route is as short as possible. If it is not possible to design it with less than 3 metres, it is advisable to insulate the dry saturated steam duct using copper or stainless steel tubing. When it is less than three metres long, rubber tubing can be used that is reinforced for high temperatures and flex-resistant.

In addition to conducting the steam to the HVAC unit or air duct, it is essential to examine the dispersion of the clean steam in the dry air. If this is not done one may have condensations inside the air duct network. These condensations may be major foci of contamination. Deposits of water in places where they are not intended to occur as per the design are a source of undesirable health problems for air conditioning installations. In addition, and becoming more important every day, we find that these instances of condensation cause major energy losses in steam production and in water treatment plants. Producing steam requires 2326 kJ of energy per kilogram of steam that we need and treating the water so that it is optimal for humidification also consumes a lot of energy. If we do not minimize these condensations the energy cost of the installation can go off the scale.

 

To study the distance of steam absorption in the air, we must know several system parameters: flow and thermo-hygrometric conditions of the air before the steam is fed in, the amount of steam supplied and the dimensions of the wetting section of the AC unit or duct. Depending on all of these parameters and on the dispersion system chosen, we will have an absorption distance that may vary from 15 cm to over 2 metres. There are various steam dispersion systems depending on the needs involved as shown in the following illustration:

A controller that incorporates equipment of this type manages the steam production so that it accurately responds to the demand of the room or process. It also manages the water stored in the tank to keep it in perfect condition in terms of both quality and content of dissolved minerals. Finally, it manages to perfection the steam absorption in the dry air flow thereby preventing condensations that would otherwise cause large energy consumptions and sources of unintended health problems due to the production of clean steam in the previous system.

 

Conclusions:

The production of clean steam is in increasing demand in a host of pharmaceutical industries for a wide variety of applications. In the event of a need for this steam for productions processes (coming into contact with the product) whose water requires an extraordinarily high quality, it is possible that systems for the production and conveying of steam made with materials of the highest quality and at a high cost will be required.

 

For the case of processes where the steam is used for HVAC purposes and as a heat-carrying fluid for other processes, it has been demonstrated in practice already implemented in the industry that the global solution may call for replacing boiler steam with sanitary grade water. These systems used in conjunction with appropriate steam dispersion systems offer a guarantee of sufficient quality steam and, unlike the other system, a safeguard in terms of the possible condensations in air ducts.

 

Bibliography:

• HARRIMAN, Lew; BRUNDRETT, Geoff; KITTLER, Reinhold: “Humidity control design guide”. Atlanta, EEUU. 2006. Editorial ASHRAE.
• LATHAM, Tim: “Clean steam in the pharmaceutical industry”. PDH Course K109. PDH Online center. EEUU. 2004
• RITE y normas UNE de aplicación. Barcelona. Editorial CEYSA
• Real Decreto 1027/2007, de 20 de julio, por el que se aprueba el reglamento de instalaciones térmicas en los edificios.
• MORTON, B. W: “Humidification Handbook”. 1998. Ed. DriSteem.

Summary: In this information sheet we discuss the importance of controlling humidity in air-conditioned, heated and/or ventilated premises, according to their specific needs of use.  In particular, we show that humidity is important not only for the comfort of occupants but also for the consequences for their health if the control of the levels required by law is deficient. We look at the current regulations on this matter, both for general use and for hospitals, to which specific requirements apply. A very important characteristic of the system is the efficient design and fitting of used vapour ducts, to prevent spills of condensate that could present the risk of creating sources of infections. Finally, we analyze the energy and economic cost of the systems used to supply humidity according to the energy source, and the equipment used. It is not uncommon for the cost of the energy associated with humidifying to result in the system being left unused.

 

Key words: Humidity, vapour, isothermic, dispersion, cost.

 

INTRODUCTION

 

There are various parameters involved in ambient comfort:

• Ambient temperature
• Ambient humidity
• Air movement through the premises
• Air quality (cleanliness, harmful gases etc.).

The effect of temperature which is well-known, and the conditions can vary from 20ºC to 28ºC, according to the circumstances.

The influence of humidity content in air is less well-known, which is why its importance is rarely acknowledged, both when it is too high and too low.

• It affects the health of the respiratory tracts.
• If high, it can cause colonies of bacteria to grow.
• It increases the effect of static electricity if it is too low, causing headaches, etc.

AVAILABLE DATA AND TECHNOLOGY

The range of required values is indicated in the Regulations on Design Conditions in air-conditioned spaces.

• Limitation in swimming pools: 65%HR, max. 30ºC.
• Return adiabatic cooler when there is heat recovery.
• Sanitation quality humidified steam.
• Interior hospital air quality requirement to UNE standard 100713.

Spaces co-exist in hospitals for many different uses, with diverse needs and different design conditions.

In cases such as consulting rooms, waiting rooms, foyers, administration areas, and also in hospitalization areas, the needs are not very different from what would be required in buildings in the services sector (offices, entertainment venues, hotels, etc.) although there may be special requirements in some cases, because there is long-term occupancy.

There is a regulation that covers the requirements for hospitals, which are generally based on the standard UNE-100.713.

It can be seen that, in general, somewhat higher temperatures apply (24-26 ºC) that those specified by the RITE regulation for winter, which can be justified in spaces for patients, but could be excessive in other spaces.

For operating theatres, delivery rooms and similar spaces, the range is greater: between 22 and 26ºC.

HVAC for operating theatres has several particular features, which are essential due to the use and conditions of the space.

–     Internal space, not influenced by outside conditions.

–     Internal and ventilation load only.

–     Very high Air Renewal Load.

–     Very strict requirements in terms of temperature and humidity.

In any case, the conditions are set by the surgeons.

It is essential to bear in mind that the system called for is an “All Outside Air” one and a Large Flow, so the increase in temperature and specific humidity in the air passing through the space is small, hence one needs to ensure that the injection conditions established are met exactly, since the inertia of the inside air is minimal.

To clarify these concepts, let us analyse a standard operating theatre:

-Surface                            30 m2

-Volume                             80 m3

-Air flow                             2,400 m3/h

Assuming:

Refresh rate                    30 refreshments/hr

Age of the air at the outlet                       2 minutes

The internal heat load of the space is determined by:

Sensitive            Lights,  Electrical-medical equipment, Persons.

Latent                  Sterilization Equipment (as applicable), Persons.

In general, we can say that the increase in temperature is usually less than 2ºC and the humidity supplied is no higher than 0.5 g/kg of inserted air.

Some typical conditions requested by surgeons for humidity injection are: 22ºC and 45% HR.

This means a specific humidity of x= 7.5 g/kg.

To meet these conditions, we require:

– In winter, supplying humidity to the intake air.

– In winter, extracting humidity from the air.

Air dehumidification is usually achieved by passing air through a coil fed with cooled water, which comes from the hospital’s general air-conditioning system; this often presents difficulties because frequently the temperature at which the cold water reaches the cold coil of the HVAC unit is not sufficiently low to dehumidify all of the air required, when the outside ambient conditions include high humidity.

There are two procedures for humidification, (supplying humidity to air):

– Isothermic humidification

– Adiabatic humidification.

Adiabatic Humidification

Air for humidification is passed through a moist panel, on which water evaporates as it joins the air current; or alternatively, liquid water is pulverized and likewise evaporates.

The process is adiabatic as the latent heat of evaporation is taken from the air itself, which cools; the enthalpy of the assembly remains constant, but the sensitive heat has been converted to latent heat.

Due to the risks of spreading Legionella and other bacteria, adiabatic systems are not normally used in hospitals.

 

Isothermal humidification

Having ruled out adiabatic systems as explained above, the remaining option is to feed steam.

Saturated steam production units are used, at atmospheric pressure (100 ºC). There are systems with heat supplied by electricity, or by an external thermal fluid, generally steam or super-heated water.

 

Electrical approaches

By Immersed Electrodes

– These require water with sufficient electrical conductivity, between 125 and 1,250 micro Siemens/cm..

The water must be of “sanitary quality”. Drinking water from the public water supply generally meets the requirements.

By Electrically resistant elements

• Will work with de-mineralized or osmotized water.
• Achieve a very accurate regulating of production.

The units have built-in systems to dispose of the deposited salts automatically.

Both systems have a high operating cost as they consume electrical energy.

 

Conventional Steam Boiler

This is expressly prohibited by the Regulations, as the steam produced does not have the “sanitary quality/grade” required.

 

By External Fluid

They are hygienic steam production units, which draw heat from an external fluid, in general, steam or super-heated water.

The production, distribution and dispersion system is illustrated in the diagram.

Steam Dispersion

Good design and implementation of the dispersion system is fundamental for the unit to work smoothly as a whole. It is not uncommon for defects in the conduction route or the poor positioning of the dispersion unit, the “steam lance”, to ruin the performance of the whole and lead to it falling into disuse.

In the following figures one can see the various units:

The importance must be stressed of positioning the lance and evacuation of the condensate produced correctly in order to prevent drips inside the HVAC unit or duct.

Absorption distance

The steam that is injected into the air current is saturated (100ºC); on coming into contact with the cooler air, it condenses, forming a mist (microscopic particles of liquid water) at air temperature, since the mass of the steam is very small in comparison with that of the air and the temperature remains without any noticeable change. This mist progressively dissipates, evaporating into the air, until it is completely absorbed.

The above process takes some time for the mixture and evaporation, so that from the injection point until full absorption, there is a section of the air current, called the “absorption distance” within which there must be no obstacles or protrusions in the conduction, to prevent the risk of liquid water being deposited on the surface in contact with the air.

To prevent this, there are various shapes of lances and graphics to select the suitable dispersion units according to the specific conditions of the site selected.

ENERGY ANALYSIS

Cost of Steam

• Example: Hospital
• Area: Cantabrian Region
• of HVAC units: 35
• Total Air Flow: 340,900 m3/h
• Winter design cond.: 0º-89%-(x= 3.4 gr/kg as)
• Winter Inside spaces:
  • Operating theatres and similar: 22ºC-45%  (x=7.5 gr/kg as)
  • Other Uses: 23ºC-50%   (x=81 gr/kg as)

 

Methodology

The needs for humidifying vary according to the outside conditions.

The data on humidifying needs have been taken from the Project Design.

The internal design conditions are:

• Operating theatres and similar: 22ºC-45% (x=7.5 gr/kg as)
• Other uses:                23ºC-50%  (x=8.1 gr/kg as)

-Areas:   24h/day, 365 days/year

12h/day, 5 days/week

Weather Data: ATECYR [Spanish HVAC Association]  “Bilbao Three-hourly Data”

Design Conditions:

• Total Humidification Capacity: 1,828 kg/h
• Total power required:
  • Water enthalpy 10ºC …………………..42 kJ/kg
  • water enthalpy 100ºC………… 2,675 kJ/kg
  • Increase in enthalpy……………2,633 kJ/kg
  • Equivalent to…………………………0.731 kWh /kg v (useful net power)
  • Assuming………………………0.8 kWh/kg (gross power)
  • Total power required:
  • 8 kWh/kg x 1,828 kg/h=  1,462 kW
• Electrical Equipment:
  • Loss Distrib. (3%)          1,507kW

Fluid Output:

– Loss Gener. and Distr. (18%)                      1,783 kW

Direct Gas

Loss  Generation (10%)                            1,662 kW

Energy costs

Energy that has to be supplied:

4,244,651 kg v/year x 0.8 kWh/kh v=  3,395,721 kWh/year

Electricity consumption: 3,395,721 kWh/0.97=     3,500,743 kWh

Gas consumption:

With fluid:          3,395,721 kWh/0.80=     4,244,651 kWh

Direct Gas:       3,395,721 kWh/0.90=     3,773,023 kWh

Cost of Electricity:     0.12 €/kWh

Cost of Natural Gas:     0.05 €/kWh

 

• Electrical Equipment
• Potential Additional Contract: 1,507kW x 0.8(Cs)= 1,200 kW
• Additional fixed cost:
• 1,200 kW x 14€/kWmonth x 12month/year= 201,600 €/year
• Gas unit (direct and indirect):
  • Not considered

 

• Electrical Equipment
• Energy Consumption:
• 3,395,721 kWh/year x 0.12 €/kWh=    407,86 €/year
• Thermal Fluid
• Energy Consumption:
• 3,395,721/0.8  kWh x 0.05 €/kWh=      212,232 €/year
• Direct Gas
• Energy Consumption:
• 3,395,721/0.9 kWh/year x 0.05 €/kWh=     188,651 €/year

 

• Electricity:
• Units
• Electrical Install. (transformers, lines, panels, etc.)
• Estimated Total Investment €782,000
• Thermal Fluid
• Unit
• Installation (boilers, pipes, insulation, etc.)
• Estimated Total Investment €630,000
• Direct Gas:
• Units
• Electrical Install. Gas
• Estimated Total Investment €365,000

CONCLUSIONS

–     Controlling humidity in hospitals calls for a considerable consumption of energy which not uncommonly means that the humidity control units are unused.

–     More often than not, this is achieved using independent units powered by electricity.

–     The technology and equipment exists to drastically reduce the running cost in comparison with electrically-powered units.

 

 

REFERENCES

 

Ashrae Handbook 2008 Systems and Equipment

Lew Harriman et al. 2006  Ashrae.