HVAC Pump fundamental
20Pages

Pumps and pipes in theory and practice The anatomy of a comfortable and cost-efcient indoor climate

Introduction For owners or administrators of a building, the comfort of tenants is not the only concern. Long-term economy and environmental aspects are every bit as important. And, if you are a building contractor or a consultant, your customer will surely trust you to share this responsible approach. This guide aims to answer some fundamental questions about heat distribution and circulation systems – from basic pump theory and energy conservation to pipe work design and how to choose the right pump for the job. Our main aim is to provide general information about conventional heating...

Creating a comfortable indoor climate There are several ways to ensure a comfortable indoor climate. This brochure describes closed heating/chiller systems where the preferred room temperature is achieved by circulating hot or cold water in pipes around the building. Such systems typically comprise a boiler or chiller, pipe work, ttings, a pump, emitters (e.g. radiators) and a control system. As water expands when the temperature rises, the system must also contain a large enough expansion tank to hold the variable volume of water in the system. The capacity of the system must be sufcient...

Determining the required head When dimensioning a heating or chiller system, both system pressure and pressure losses have to be taken into account. The system pressure is the part of the pressure not created by the pump. It is generated instead by the weight of the water column in the system and additional pressure created by the pressure vessel (expansion tank). If this pressure is too low, it can generate noise in the pipe system and cause cavitations in the pump, especially at high temperatures. It must also be veried that the pump can withstand the maximum system pressure. The system...

Basic pump theory In a loop system, the weight of liquid on the way up is balanced by the liquid on the way down. Therefore, when the system is lled, the geodetic head for the building is zero, regardless of the height of the building. The required pump capacity is determined instead by the total length, diameter and routing of the pump system. See the Ferris wheel illustration below. The system curve describes the resistance that exists in the pipe system, i.e. all losses in the pipe work. Since a circulation system is usually a closed loop system, there is no geodetic head to overcome,...

How much energy is lost in the pipe work? Efciency and best efciency point The best efciency point (BEP), or nominal point, is the point at which the maximum level of efciency is achieved. The efciency curve shows how the efciency varies at different ows. In order to calculate a system curve, you must rst calculate the friction losses (hf) in the pipe work. These occur at bends and in valves (known as point losses or hfp), as well as in straight pipe sections (hfr). Point losses depend on the number of bends and valves in the pipe system, and increase with liquid velocity. Losses in...

Regulating the pump ow The capacity of a circulation system can be regulated in different ways, using pumps with speed control, throttle valves, a bypass system or reduced impeller diameter. Speed control Variable speed can either be achieved manually with xed multi-speed pumps or automatically, using electronically controlled pumps. Apart from reducing energy consumption, a speed-controlled pump will always run at optimal differential pressure. This will minimize the noise in the pipe system and increase living comfort. deliver the required pressure. When demand increases, the pressure...

Other ways to regulate the ow Here are a few other ways to control the ow in your system without using a speed control unit. This will give you a lower initial cost, but lowering the ow will not reduce energy consumption, and the life cycle cost will not be reduced. Throttling the ow with a valve alters the losses in the system and thereby the ow from the pump. At a low ow the pump will produce a lot of unnecessary head, which leads to excessive energy consumption (as shown in the gure below). In a bypass system the pump is always running at full speed. The ow has a bypass loop, and the ow...

Pump economy and environmental care The total cost of pumping is largely determined at the very outset, i.e. when the circulation system is designed. Intelligent system design can help to minimize the resistance of components and friction in the pipes that must be overcome by the pump. This in turn reduces the amount of energy required to circulate the water. This is, by far, your best opportunity to optimize pump economy. To give you an example, the friction loss increases as the square of the velocity increases. This means that a pipe with a small diameter will have a much higher friction...

1. Use pumps with variable speed control, as they use up to 70 % less energy than an uncontrolled pump running at full speed all the time. This is the single most effective way to reduce the total operating cost – the payback time for an investment in speed control is often less than two years. 2. Look for high-efciency pumps and motors. For example, EFF1 motors (supplied by ITT) are 3 – 5 % more efcient than EFF2 motors. Another vital factor is efcient hydraulics, which can be even more important for energy efciency than the pump motor. ITT’s in-house experts invest considerable effort to...

Pipe work design In the early stages of the design process it is necessary to consider potential zoning needs, alternative heating or cooling sources, and operating and control strategies. Based on the information gathered about the building you also need to calculate space heat losses and assess the hot water system demand, as well as various ventilation aspects. Before designing the pipe work you must also determine that you have selected the most suitable emitters and connections for each position and consider the best distribution layout, taking into account all necessary balancing and...