By nature, terminal units (fan coil, radiator, AHU,) close to the pump are working in overflow creating underflows in others terminal units.

For instance, in heating system, it frequently happens that rooms close to the boiler room and then close to the pump are  in overflow and consequently overheated, whereas rooms further away reach the temperature with difficulty. Room temperature deviation reaches easily 2°C to 4°C.

This situation also leads to a higher total flow than required and therefore increases electrical pump consumption and poor power transfer at interfaces.

This conducts most of the time to put more productions units (boilers, chillers) into operation than would normally be necessary and affects the efficiency of condensing boilers or the chillers COP.

These different effects can globally create together an over-consumption from 10% up to 35%!

Reference case:

Granloholm, residential area in Sundsvall, Sweden.  15% energy savings 

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TA-SCOPE	STAF	DA 516

When the distribution pump is oversized and the system is unbalanced, the distribution takes more flow than the production can provide. This creates a mixing point between return water and supply water at the outlet of the bypass between de production and the distribution sides.

In cooling, due to this flow incompatibility, the supply water temperature is higher than expected per design and the terminal units could not deliver their full power capacity creating uncomfort for the occupants.

Decreasing the set-point of the production units can compensate for the incompatibility but at the cost of higher energy consumption. Chiller manufacturers’ technical literature indicates extra energy use of approximately 4% per °C that the chilled water supply temperature is lowered.

Reference case:

Citate Administrativa in Minas Gerais, Brazil. 21% energy savings.

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STAD	STAP	DA 516

A  lower return temperature than design can result from different hydronic failures such as:

• A non control flow passing through a bypass pipe and creating a mixing between cold water supply and the return
• The use of 3 ways control valves instead of 2 ways when possible.
• A non balance plant making terminal units working globally overflow
• A pump head setting point not well adjusted

A lower return temperature is reducing the temperature difference  DT = Ts – Tr (Ts: Supply temperature; Tr: Return temperature) and then the log mean difference between the fluid and the refrigerant affecting significantly the COP by up to 15%.

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STAF	TA-FUS1ON-C

In heat exchanger applications, the deposit of dirt on the internal surface of the pipe is acting as an insulation effecting the heat transfer and the pressure drop. This increase of pressure drop will affect the electrical pump consumption.

The thermal impact of fouling is often expressed in term of fouling resistance, Rf, which can be approximated by: Rf = d/lf with d is the thickness and lf the thermal conductivity (*).

(*) Publication: On line “Heatexchanger-fouling.com”

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Compresso	Transfero	Statico

To get condensing boiler high efficiency the return water temperature needs to be kept below the vapour dew point in exhaust gases and thus DT has to be kept high. This is achievable only by having stable and accurate modulating control of variable flow in terminal units and by avoiding overflows due to unbalanced system.

In a system working over flow the return temperature is higher than normal. The number of days of condensing capacity is then reduce by up to 20%. Considering 15% energy saving due to condensing technology the impact of overflow is estimated at 3% of the boiler energy consumption .

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STAD	STAP	TA-FUS1ON-P

A poor pressure maintenance system (bad sizing, quality issues,…) conduct most of the time to regularly  make up fresh water to compensate leakage on the safety valves due to over-pressure.

The fresh water contain scale that deposit mainly on the hottest  surfaces (boiler exchanger)  of the heating system.

This deposit is acting as an insulation effecting the heat transfer and the pressure drop. This created a lose of boiler efficiency and then a higher energy consumption. Over than that a thermal cavitation is locally created by the scale deposit damaging dramatically the boiler.

In parallel of the scaling the fresh water containing oxygen will create corrosion and thus magnetite dirt deposit all over the heating system.

(*) Results of tests made by University of Illinois and the U.S. Bureau of Standard

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Zeparo-ZUD	Zeparo-ZIO	Zeparo-ZEK

The pumping power consumption is directly proportional to the water flow, the pump head and the efficiency of the pump and the motor. In cooling,  the energy provided to the pump itself and transferred to the water has to be compensated by the chillers . Therefore pumping energy needs to be paid twice in cooling:  at the pump and at the chiller!

An estimation of how much represents the electrical pump consumption compared to seasonal energy consumption of the plant working at constant flow is given by the formula below:

Remark: In heating, a recent research demonstrates that pump consumption represents 1.5% of the energy consumption in buildings such as offices, schools, hospitals in Sweden.  "Efficiency of building related pump and fan operation", PhD thesis by Caroline Markusson, Chalmers University of Technology, May 2009

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TBV-CMP	TA-FUS1ON-P	DA516

Pumping costs are proportional to the product of the pump head by the flow. Unbalanced systems typically run too high total flow to compensate for local underflows. It is quite common to observe that flow in distribution is 50% over than the design value (*)

Proper balancing brings also the possibility to optimize the set-point of the variable speed pump (savings on pump head depend very much on projects but pumps are always oversized by at least a 10% safety factor taken by design engineers).

Considering a plant working at 30% over flow and only 10% over pump head, by well balancing the system the saving obtain on the pumping energy is already 40%.

Example:

A. System non balance: 

Pump consumption 12.8 kW (100%)

B. System balance: 
Pump consumption 10,2 kW (80%)

C. System balance and Pump head adjustment 
Pump consumption: 7.31 kW (57%)

(*) Source: Investigation by Costic (French Research and Training Centre in HVAC), published in CFP Journal April-May 2002.

Reference case:

Hammarplast Consumer factory, Sweden. 61% of pumping energy savings.

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STAD	STAP	TA-SCOPE

It is quite common that people increase the total pump head to compensate under flow in some part of the system.

To compensate an underflow of 20% in some terminal units the total flow should be increased by 25% (0,8x1,25 = 1). Since the pressure drop of the system increases with the square of the flow, the pump head must be increased by 56% (1,25x1,25) to provide the required flow increase.

Such increase of pump head is obtained most of the time by changing the pump impeller or by installing a more power full one.

Considering pump and motor efficiency remain the same, as electrical pumping costs are proportional to the product of the pump head by the flow, this situation will create an over-consumption of 1,25x1,56 = 1,95 so 95% higher than the normal consumption.

Remark: Instead of changing the pump some people use the back-up pump running in parallel with the pump normally use.  This creates over pump consumption too.

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STAD	STAP	TA-FUS1ON-C

To compensate for hydronic problem and too low or too high room temperature it is quite common to observe that supply water of the HVAC system is increased (in heating) or decreased (in cooling).

This will create overheated or overcooled rooms in the most favoured part of the building. It will also impact the heat losses or heat gains of the pipes reducing the global efficiency of the HVAC system.

In heating, considering water at an average temperature of 50°C and the external temperature of the pipe at 20°C, the heat losses increase by 3% for each water degree higher than design.

To compensate a room temperature 1°C too low, the temperature of the water should be increased approximately by 4°C (depending on the design conditions), meaning that pipe heat losses will increase by 12%!

     Simplify formula for heat pipe losing calculation 

With:

Pm: Pipe heat loses per meter (W/m)
DT: Temperature difference between water and ambient temperature
de: Pipe external diameter (mm)
l: insulation thickness (mm)
: insulation conductivity (W/m.K)

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Pipe pressure drops often called linear pressure drops depends on:

• The pipe internaldiameter
• The pipe roughness
• The water (heattransferfluid) density and viscosity
• The flow

Oxygen presence due to poor pressure maintenance  creates corrosion . Dirt deposit due to bad water quality and too low water flow velocity in some parts of the plant modify consistently the pipe roughness in  the first years by + 15% to +70% and after 20 to 50 years by +150% to +24000% (**).

To compensate  for this increase in pressure drop the pump head needs to be increased by the same amount. By the consequence the electrical pump consumption is increasing.

For example: (*)Considering pipe pressure drop representing 50% of the total pressure drop of the system. An increase of 70 % of the pipe pressure drop directly impact the electrical pump consumption by 35% to get the same flow.

(**) Source: Result publish by Utah State Universty, Prof. Rahmeyer

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In heating the over consumption of a building is directly link with the temperature difference between the room temperature and the outdoor temperature.

This over-consumption can be estimated by the following formula:

S%: Over Energy consumption express in % for 1^oC increase in the room temperature
S_c: Ratio between the average seasonal heating power and the maximum necessary power
t_ic: Design room temperature
t_ec: Design outside temperature
ai: Internal heat gain expressed in degrees of influence on the room temperature

Example:

For t_ic = +20^oC, t_ec = -10^oC, ai = 2^oC and S_c = 0,4

The over energy consumption S = 9%

Stable and accurate room temperature control provides comfort to people and it is one of the most powerful action to reduce building energy consumption.

Reference case:

MOL, Hungarian Oil and Gas corporation, Hungary. 27% energy saving.

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In cooling system, if the room temperature is for instance 23^oC instead of 24^oC (1^oC too low) it creates an over-consumption that is directly linked with the load on the building (internal and external heat gain).

This over-consumption can be estimated by the following formula:

S%: Over Energy consumption express in % for 1^oC decrease in the room temperature
S_c: Ratio between the average seasonal heating power and the maximum necessary power
t_ic: Design room temperature
t_ec: Design outside temperature
ai: Internal heat gain expressed in degrees of influence on the room temperature

Example:

For t_ic = +23^oC, t_ec = 35^oC, ai = 4^oC and S_c = 0,4

The over energy consumption S = 16%

Stable and accurate room temperature control provides comfort to people and it is one of the most powerful action to reduce building energy consumption.

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In variable volume system using 2 ways control valves in On-Off control mode when some valves are closed the pipe pressure drop decreases provoking over available pressure for circuits still open. This create an over flow modifying the electrical pump consumption and the return temperature to the chillers or the condensing boilers.

At 50% of the load an On-Off system could provoke an over flow up to 50%(*) higher than the normal flow. This creates an over pump consumption during the cooling season up to  3%  (*) of the total cooling energy cost.

The return temperature is affected too by 1.5°C to 2°C at 50% load creating  a decrease of chillers  COP by up to 4% (Fact 2).

Cumulating this two aspects an On-Off control system is creating up to 7% energy increases. On which we could add the over-consumption due to room temperature deviation.

The adapted balancing procedure should be apply to get the right flow for all terminal unit and avoid hydronic interactivity.

(*) Mathematical modelisation (Hydronic College, Jean Christophe Carette)

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Energy can be saved by reducing (heating) or increasing (cooling) the room temperature during the non-occupancy period or during the night. The longer is the set back period, the higher is the energy saving.

Energy saving obtain thanks to set back temperature could be estimate by:

t _{set back} (hours): Period during set back temperature
t _set (hours): Period of set temperature
T _{set back} (°C): Set back temperature
T _set (°C): Set nominal room temperature
E _{saving (1°C)} (%): Energy saving for 1°C lowering the room temperature

Considering a room maintained at 20°C from 8 am to 6 pm (10 hours) and a set back temperature 3°C lower (17°C) during the rest of the day (14 hours) and considering each degree representing a saving of 10% (fact N°14) then energy saving can be estimated in % at: 17,5% (*)

(*) Remark: this percentage does not take into consideration the impact on the efficiency of the producer (boiler, heat pump,…) working at full load after the set back period to reach the set temperature.
Publication: “The energy saving potential of E-Pro”(Heimeier) study made by Prof. Dr. Mathias Fraaß, WOF-Planungsgemeinschaft Berlin, 2006

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An unbalanced system makes the startup difficult with some rooms taking a substantially longer time to reach the target temperature from the set-back level. This situation forces people to startup their system earlier than necessary increasing  the energy consumption. If  for some  hydronic failures the start up needs to start 1 hours earlier than normally the adding energy consumption will be: +1,25% (*)

In some building due to too high difficulty to reach the comfortable room temperature after the set back temperature period it is decide to cancel the programming functionality of the controller loosing then up to 20% energy!

(*) Considering formula on fact N° 15

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Taking into account, the thermal behavior of individual house, external weather condition during the winter, type of boiler and people behavior, the University of Dresden has conducted a study demonstrating the impact of using thermostatic radiator valves compare to manual one.

Considering:

• Heating system design at 90°C/70°C
• An insulated building following German standard 1982
• A condensing boiler

the energy saving is estimated at 28%, when comparing thermostatic valves with manual one fully open.

With a system design at 70°C/55°C the saving is 19%.

Study: Technical  University of Dresden, Institute of Power Engineering, Chair of Building Energy System and Heat Supply

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The presence of air in water must be minimized not only to reduce corrosion, risk  of cavitation and noise, but its presence also reduces emission from terminal units.

The thermal picture (see picture example) shows that the creation of air pockets prevents water circulation in the radiator and affects dramatically the power output.

To react to the uncomfortable situation created by lower radiator emission users increase outlet temperature of the boiler and pump velocity. This impact significantly the energy consumption of the heating system ( facts N°4, N°8,N°12).

(*) Thermal picture from Research group ‘Energy & Sustainable Development’

Karel de Grote University College, Department of Applied Engineering, Antwerp, Belgium

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Dresden University (Germany) has conducted a research to investigate the energy savings potential from replacing thermostatic radiator valves older than 1988 with “new” thermostatic radiator valve. As it result of these investigations, it can be stated that reductions in the room temperature can be achieved by replacing  existing TRVs with new ones (no target room temperatures undershot, less overheating, greater adherence to target values). This better room temperature control provides energy saving that depends on design temperature condition as indicated in the table below.

(*) TUD, Institut für Energietechnik, Professur für Gebäudeenergietechnik und Wärmeversorgung (Dresden University study)

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The pictured curved lines show that the nominal values of the operational room temperatures in the main usage zones are very close to the 20°C set point in case of individual room temperature control.

The values for cases where the system is not equipped with an independent local control device show an operational room temperature that is approx. 1.5 - 2 K higher. (extract of the study mention below)

This room temperature deviation impact the energy consumption up to 20% (Fact 12)!

Study: Energy and Costs Savings by Re-Fitting Individual Room Temperature Control Systems for Floor Heating by Joachim Plate (Managing Director of the Association for surface heating and surface cooling in Germany).

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