Hot-water baseboards

Hot-water baseboards and radiators require water between 160° and 180°F (71° and 82°C) to effectively heat a room. Generally, flat-plate liquid collectors heat the transfer and distribution fluids to between 90° and 120°F (32° and 49°C). Therefore, using baseboards or radiators with a solar heating system requires that the surface area of the baseboard or radiators be larger, temperature of the solar-heated liquid be increased by the backup system, or a medium-temperature solar collector (such as an evacuated tube collector) be substituted for a flat-plate collector.

There are several options for incorporating a liquid system into a forced-air heating system. The basic design is to place a liquid-to-air heat exchanger, or heating coil, in the main room-air return duct before it reaches the furnace. Air returning from the living space is heated as it passes over the solar heated liquid in the heat exchanger. Additional heat is supplied as necessary by the furnace. The coil must be large enough to transfer sufficient heat to the air at the lowest operating temperature of the collector.

DISTRIBUTING HEAT FOR LIQUID SYSTEMS

DISTRIBUTING HEAT FOR LIQUID SYSTEMS

You can use a radiant floor, hot water baseboards or radiators, or a central forced-air system to distribute the solar heat. In a radiant floor system, solar-heated liquid circulates through pipes embedded in a thin concrete slab floor, which then radiates heat to the room. Radiant floor heating is ideal for liquid solar systems because it performs well at relatively low temperatures. A carefully designed system may not need a separate heat storage tank, although most systems include them for temperature control. A conventional boiler or even a standard domestic water heater can supply back-up heat. The slab is typically finished with tile. Radiant slab systems take longer to heat the home from a "cold start" than other types of heat distribution systems

Specialty or custom

Specialty or custom tanks may be necessary in systems with very large storage requirements. They are usually stainless steel, fiberglass, or high temperature plastic. Concrete and wood (hot tub) tanks are also options. Each type of tank has its advantages and disadvantages, and all types require careful placement because of their size and weight. It may be more practical to use several smaller tanks rather than one large one. The simplest storage system option is to use standard domestic water heaters. They meet building codes for pressure vessel requirements, are lined to inhibit corrosion, and are easy to install.

STORING HEAT IN LIQUID SYSTEMS

STORING HEAT IN LIQUID SYSTEMS

Liquid systems store solar heat in tanks of water or in the masonry mass of a radiant slab system. In tank type storage systems, heat from the working fluid transfers to a distribution fluid in a heat exchanger exterior to or within the tank.

Tanks are pressurized or unpressurized, depending on overall system design. Before choosing a storage tank, consider cost, size, durability, where to place it (in the basement or outside), and how to install it. You may need to construct a tank on-site if a tank of the necessary size will not fit through existing doorways. Tanks also have limits for temperature and pressure, and must meet local building, plumbing, and mechanical codes. You should also note how much insulation is necessary to prevent excessive heat loss, and what kind of protective coating or sealing is necessary to avoid corrosion or leaks.

he liquid flows rapidly,

he liquid flows rapidly, so its temperature only increases 10° to 20°F (5.6° to 11°C ) as it moves through the collector. Heating a smaller volume of liquid to a higher temperature increases heat loss from the collector and decreases the efficiency of the system. The liquid flows to either a storage tank or a heat exchanger for immediate use. Other system components include piping, pumps, valves, an expansion tank, a heat exchanger, a storage tank, and controls.

LIQUID-BASED ACTIVE SOLAR HEATING

LIQUID-BASED ACTIVE SOLAR HEATING

Solar liquid collectors are most appropriate for central heating. They are the same as those used in solar domestic water heating systems. Flat-plate collectors are the most common, but evacuated tube and concentrating collectors are also available. In the collector, a heat transfer or "working" fluid such as water, antifreeze (usually non-toxic propylene glycol), or other type of liquid absorbs the solar heat. At the appropriate time, a controller operates a circulating pump to move the fluid through the collector.

OTHER CONSIDERATIONS

OTHER CONSIDERATIONS

The location of your thermostat can affect its performance and efficiency. Read the manufacturer's installation instructions to prevent "ghost readings" or unnecessary furnace or air conditioner cycling. To operate properly, a thermostat must be on an interior wall away from direct sunlight, drafts, doorways, skylights, and windows. It should be located where natural room air currents–warm air rising, cool air sinking–occur. Furniture will block natural air movement, so do not place pieces in front of or below your thermostat. Also make sure your thermostat is conveniently located for programming.

CHOOSING

CHOOSING AND PROGRAMMING A PROGRAMMABLE THERMOSTAT

Most programmable thermostats are either digital, electromechanical, or some mixture of the two. Digital thermostats offer the most features in terms of multiple setback settings, overrides, and adjustments for daylight savings time, but may be difficult for some people to program. Electromechanical systems often involve pegs or sliding bars and are relatively simple to program.

When programming your thermostat, consider when you normally go to sleep and wake up. If you prefer to sleep at a cooler temperature during the winter, you might want to start the temperature setback a bit ahead of the time you actually go to bed. Also consider the schedules of everyone in the household. If there is a time during the day when the house is unoccupied for four hours or more, it makes sense to adjust the temperature during those periods.

Electric resistance

Electric resistance systems, such as electric baseboard heating, require thermostats capable of directly controlling 120-volt or 240-volt circuits. Only a few companies manufacture line-voltage programmable thermostats.

The slow response time -- up to several hours -- of steam heating and radiant floor heating systems leads some people to suggest that setback is inappropriate for these systems. However, some manufacturers now offer thermostats that track the performance of your heating system to determine when to turn it on in order to achieve comfortable temperatures at your programmed time.

Alternately, a normal programmable thermostat can be set to begin its cool down well before you leave or go to bed and return to its regular temperature two or three hours before you wake up or return home. This may require some guesswork at first, but with a little trial and error you can still save energy while maintaining a comfortable home.

Figure 7 The figure show

Figure 7 The figure show SPF results from two different SPF, “heat only” and “heat and DHW” (domestic hot water heating) at two different levels, “SPF 1” and “SPF3”, from field testing.
The conditions for measurements in a laboratory and in field differ with respect to various factors e.g. the boundary conditions. SPF1 in field measurements includes the electrical energy from the heat source brine pump, while “average COP” and “SCOPnet” only includes the head losses. This could make the electrical energy use a little larger for the field measurements, but on the other hand “average COP” and “SCOPnet” also contain head losses for the heat sink side which SPF1 does not. The electrical energy from the heat sink pump for SPF1 is included in SPF3.

shows a trend that SPF1 is higher compared to “average COP” and “SCOPnet”.

Figure 8 The figure shows a trend that SPF1 is higher compared to “average COP” and “SCOPnet”. Field measurements imply a higher uncertainty compared to measurements in a laboratory. The bars of error show an error of ±10% to cover the margins of error.
There are two main differences between “average COP” and “SCOPnet“:  There are differences in degradation for part load operation  Lot 1 does not make an capacity balance of the heating demand of the house at each outdoor temperature.  
The last factor results in that the design capacity, Pdesign, turns out to be larger for the house when using SCOPnet compared to “average COP”. The result show that Pdesign for “average COP” is approximately 13-28% lower compared to “average COP” and SPF is approximately 3-4% lower. The degradation of COP is a little bit tougher when using Lot 1 compared to using prEN14825. The comparison is illustrated in Figure 9 below

Air to air heat pum

Air to air heat pump Laboratory test data was available for one of the air to air heat pumps that were studied in field. SPF from the field study and SPF from the calculation models are presented in Table 10 below. SCOPnet is the SPF for the heat pump that corresponds to SPF1. SCOPon is SPF for the heat pump with the backup heater included and corresponds to SPF2. SCOP is SPF for the heat pump with both backup heater and parasitic losses included. There are some problems by comparing the laboratory test data and the data from field testing, since the field tests do not include the defrosting periods. Therefore SPF from field testing might turn out a little higher than in reality.

Conclusions from comparisons

Conclusions from comparisons
Some of the field installations show different SPF1 despite that the same heat pump model is installed. This can be an indication of how important the sizing of the heat pump is. An oversized heat pump results in for example more part load operation and causes standby losses.  
The calculation models show that there can be benefits when installing a heat pump where the bivalent temperature is higher than the lowest operation temperature of the year, even though backup heating is necessar